- Six Diligence 2010

Wednesday, April 20, 2011 ;

http://fishindex.blogspot.com/2009/02/barreleyes-macropinna-microstoma.html

hello people! (: long time no see and chat xP I miss you guys! so anyway, I was searching for information on the blobfish and I just came across this. It's kinda weird but interesting at the same time. Click on the link above (points up) to know more about the Barreleyes ^^

till the next time we meet,

adios for now!

Lydia :D

posted by `[x] imLYDIA {: ♥ at 11:20 PM | 0 Comments

Sunday, April 3, 2011 ; Structural Adaptation

Enjoy~

posted by Allan at 1:04 AM | 0 Comments

Sunday, October 10, 2010 ; Questions

Dear pupils,

Here are the questions that I asked mr wan:

Michelle : What is greenhouse gases? the definition? effect? affect?

Mr Allan Wan: You only need to know carbon dioxide is one of the greenhouse gases and all greenhouse gases trap heat.

Me: mr wan, if you put a plant in blue dye, then put in clean water, will the stem still have blue colour?

and water is used to photosynthesise, so if it uses blue dye, will the food be blue too?

if it won't, what will happen to the blue dye then? will it escape through the stomata?

Mr Allan Wan: First of all, you won't really see the stem change colour as water carrying tube are inside the stem, not outside

usually the leaves and flowers change colour

if the plant absorbs more plain water, i guess the blue just becomes lighter and lighter

colour won't escape from stomata, only water and gases. The colour simply becomes lighter over time.

Me: why?

so do you mean that the leaves only take the clean water and not the blue coloured dye for photosynthesis?

Mr Allan Wan: Nope, the blue just gets paler and paler as it mixes with more clear water

Me: ohh.. but will it disappear totally?

Mr Allan Wan: It's more of diluted. Like a sweet drink, if you add more plain water, it gets less sweet but it doesn't mean the sugar disappears

Me: ooh... but the water is used up, not the blue dye

Mr Allan Wan: water mixes with the blue until the blue becomes diluted and no longer visible

That is the questions that I remember. Sorry, my memory is not good.

Michelle

posted by 6 Diligence at 7:25 PM | 0 Comments

Saturday, October 9, 2010 ; 6D's questions

Michelle:

7A:

17) You told 6H that option (3) is a scientific fact, but not based from results above.

????? (3) The greater the spring compression, the greater the amount of elastic potential energy the metal ball has.

????? But shouldn’t it be spring and not metal ball? How could a solid be compressed?

I read it as greater amount of EPE for the spring, my bad. Metal ball has no EPE. If the question is "The greater the spring compression, the greater the amount of elastic potential energy the spring has", it is just a fact, not from the results.

3E:

3) Why is it that heat is depended on mass? The heavier you are, the more the heat? Somehow, option (4) makes sense.

Heat dependent on mass is more of latent heat concept and is a physics science principle. Heat's relationship to mass has never been tested in PSLE. I don't know how to explain option (4) in primary school context.

4) If they give a graph on population for each month of a species, how do you know when is aug, sep, oct, if they didn’t state in the question?

When they put Aug, they're asking you to compare July's population with August's population.

10) A: There was heat gain only during BC. (I thought it could go beyond Boiling Point, like ice?)

As long as there is temperature difference between 2 bodies, there'll be heat exchange, including melting ice at 0 degree Celsius. In actual fact, there is heat gain from A to D. A to C, heat is gained by water/ice. C to D, heat gain by surrounding.

?? B: Water existed in two different states during AB. (water evaporated, forming water vapour. When it evaporate, is it gaining or losing heat?)

Evaporation is always heat gain as water molecules gain enough energy to leave the water surface. So yes, there're 2 states: gas and liquid.

?? C: Evaporation of water took place during BC and CD only. (Evaporation occurs anytime, anyplace as long as there are two different temperatures. Rate of evaporation is affected by the difference in the two substance)

Yup, evaporation takes place at all times.

?? D: It took 6 minutes for the water to reach boiling point. (Yes, Interpretation of Graph)

Correct

11) Is it a fair experiment? Because there are two different people pulling the carts, and there is also the absence of wheels.

First of all, it was not an experiment. Secondly, it was for comparison. Remember the hanging magnets of different strengths? They're of different distances from the nails as well. There are 2 changed variables, yet you can find out by comparing. Not all science results are derived from fair experiments. Fair experiments only allow you to pinpoint which exact variable has an effect on the results.

12) Why is A correct? That block is one block, why is volume affected?

X has a deeper dent than Z, meaning there was more impact. Since height from the ground is the same, we can only look at mass to determine how much KE was converted from GPE. A higher mass means higher GPE and more GPE to convert to higher KE.

Yun Ling:

Firstly...
A) sunlight + live plant
B) sunlight+ dead plant
c) opaque box + live plant
d) opaque box + dead plant

there are limewater in each of the set ups

my ANS:The limewater in a,b and d will turn chalky.
C: Decomposition & photosynthesis give out carbon dioxide

but the answer given was b, c and d
My answer is b,c,d too. Firstly for a), sunlight and living plant means plant phtosynthesises, giving mainly oxygen, not carbon dioxide. For (c), I've told you during PSLE Booklet that plants compete for oxygen in darkness as there is no light to trigger photosynthesis, so there'll be carbon dioxide given in (c)

2ndly...
Could you type in some notes on the circulatory system?
I came across this question and i copied notes from the board and it wrote that: from lungs to heart, the blood is rich in oxygen, and food. From other parts of the body to heart, theres waste material and poor in oxygen.
How is there food in the heart, and how do we breathe out waste material? :P eww..
So could you just write down stuff about what blood contains from lungs to heart, heart to other parts of body, other parts of body to heart, and heart to lungs. And about small intestine to heart too (i think it goes to the heart if im not wrong...), plus anything else that i should take note of.
I'll post this in the 6D blog.

3rdly...

A: water snails in water, in air tight lid
B: hydrilla and water snails ini water, in air tight lid

both containers must be placed near the windows because ...?
Ans given: It is to ensure that there is only one changes variable, which is the presence of hydrilla. Sunlight enables the hydrilla to make food.
It was to make sure that location for both set-ups do not change and mainly for the hydrilla to make food.

What im thinking is that the change variable is that B has ''something'' that provides dissolved oxygen. So without the sunlight, the ''thing'' cannot make food, and therefore the experiment set-up is not related to the aim.

i thought it should be:
The hydrilla needs sunlight to photosynthesize, withought sunlight, the hydrilla cannot make food and give out oxygen. Therefore, snails will die. There can only be 1 changed variable in an experiment, which is the presence of hydrilla that produces oxygen, in order to have a fair test. Other variables have to be kept the same so that it would not affect the survival of the organisms, therefore, both set-ups must be placed near a window where there is sunlight.

So i would be explaining why B has to be near sunlight in the first place (explain why not both placed somewhere NOT near sunlight), then explaining why A has to be near sunlight (fair test)
Could you type in a better answer is you have one? or do i just write in those given, (it's only 1 mark question)

I'd have written: This is a fair experiment that has only one changed variable, which is the presence of hydrilla. Other variables like location of set-up and amount of light cannot be changed. This is to ensure that the results is not affected by changes in the amount of light the set-ups are exposed to.

4th Question...

Garden soil has more nutrients, more air spaces between soil particles, less evaporation at the surface and retains more water.
Why is it less evaporation at the surface? For sand, the water trickles down due to gravity, so isnt it less water at the surface? But garden soil retains more water so theres more evaporation at the surface? oh and i thought it has less air spaces so it can retain water?
Water evaporates more easily from cotton than garden as cotton is not soil and it does not retain water as well as soil.

Explain the effect that temperature has on the reproduction rate of the bacteria: The higher the temperature, the higher the reproduction rate of the bacteria.
I thought that the answer was inaccurate as they will eventually die when it gets too hot.
Should we write this instead? : A lower temperature has a slower reproduction rate of the bacteria
Yes, but also write that a temperature too high will kill the bacteria.

A transparent object allows light to pass through, so why is there still a shadow?
No matter how transparent you are, you'll still block some light, particularly at the sides. But in primary school, we take it as either a pale or no shadow.

When boiling water in kettle, water evaporates to become steam, then the warmer steam condenses on the colder air. Then after that the steam disappears, its evaporation. But why evaporate again? the steam lost heat to the surroundings then condensed... then it gained heat from the environment again...? I can't really think why that happens somehow. is it anything to do with the SLG line thing?
Firstly, steam cannot be seen and it's the tiny water droplets that evaporate. Water always gain heat and evaporate, at all temperatures. Nothing to do with SLG. Water is a special substance.

We stick a candle on the bottom of a cup, turn it upside down and immerse it in a trough of water. does the volume of air in the cup change? Because oxygen is used up but carbon dioxide is given out (is there a formula for this btw?). if there is a change, then some water will seep through am i right? but the gravity pulls the cup down, so the gap isn't that big, but water still will seep through?
I don't quite get the question but burning will take away oxygen with little replacement. An upside down candle burns faster too as the flame touches the wax straight away. Water will enter the cup to replaced the oxygen used for burning.

For evaporation, does exposing it to sun or wind speed up the rate of evaporation of water?
My opinion is wind is faster than sun as wind blows away the water molecules at the surface while sun heats up the molecules and they have to gain enough heat energy to leave the water surface.

There's a beaker, we put a stopper in the opening and a funnel through the stopper, water in the funnel, the water will drip slowly. Eventually, the air will be compressed to the MAX so water can't drip in anymore to occupy its space. But why cant the air dissolve in the water in the funnel then escape? will it even escape or maybe is it too little that we cant see anyway? (i dont think this really matters :P)
When air dissolved in water, it increases the volume in the water too. Why do you think Coca Cola makes so much money? It's feeding you guys air! hahaha

Inhaled air contains more germs and dust particles?
Erm, we shouldn't give such answers. Anyway, some people's exhaled air got more germs! Some rooms are clean with very little dust. So we use amount of carbon dioxide, oxygen and warmth to compare.

But how do we explain how size of shadow changes according to distance from the light? and for the one where the shadow changed at diff time of day. (both in booklet B)
When we simple write because of the different angles, it doesn't really explain much.
How about "The person block different amounts of light from the sun which is at different angle from the person throughout the day, so the length of the person's shadow changes according to how much light she blocks."

and what is the difference between sugar and starch. Is it plants make sugar because sugar=food and store it as starch? But then for a normal flowering plant we don't see any parts swelling up that store food, so where is it stored? in the leaves or stem? (anything to do with sap?)
Starch is excess sugar. Sugar is food made by plant, so you can say starch is excess food. Do take note that starch cannot be transported through food-carrying tubes. Food is stored in numerous places, abundant in leaves, underground stems and roots though.

for experiments the stuff in the setup have to take time to give a result, if they don't give you a specific timing, can u just make it up? for example: leave the experiment for a day, then..... measure.....
Yes, give a reasonable timing. Also, check if the question hints or requires a specific timing.

For cactus, if the leaves don't make food, why are they leaves? the stems make food. Leaves are there to carry out transpiration and also to discourage animals from biting the juicy cactus. They're known as modified leaves as well. Yes, stem of cactus makes food.

what is the purpose of sap? its always written that it just keep plants firm and upright, isn't it storing water and food or something? that should be the main purpose and is it the sap or the cell wall that has similar function as skeletal system?
Cell wall is more of skeletal system. Central vacuole is like the water in a water balloon, giving it certain amount of stability. Yes, it stores sap, a form of water.

For experiments, does it always have to be "to find out if ___changed v___ affects __results___?
like for example can we write both of the following?

She was trying to find out which type of soil is suitable for the baby catfish

To find of if the type of soil in water affects the number of catfish living in the water?

it's like the first one makes more sense but the 2nd one somehow feels safer

Both are correct. The second one is for those who are weaker in science to "memorise" how to answer "aim questions".
I'd write "affects the population of the baby catfish" for the second one though. Be more specific to the age of the catfish.

Pheobe:

1. is air pressure is syllabus?
No, just treat it as air occupies space.

2. why does the bottom metal of a bimetallic strip have to bend more than the metal on top?
It may not be the bottom metal all the time. The metal that bends more reacts more (expands more) to heat and causes the bimetallic strip to bend towards the less reactive one.

3.what are some of the effects of oill spill that we are supposed to know about?
You're supposed to know that it can kill lifeforms. How it kills lifeforms is not tested but it's certainly good to know.

4. are the different type of teeth like incisors in syllabus?
You don't need to know the name of different teeth but you need to know how different teeth function. Eg incisor is for cutting plants like leaves and stems, canine is for sinking deep into the flesh to grip the prey tightly, molar for grinding plants or flesh. There're different molars for carnivore and herbivore. Carnivore's and omnivore's canine are sharper. Herbivore's molar are less sharp.

5. for the addition PSLE booklet questions, for question 30 (c), i don't get why the answer is 1994-1996 instead of 1995-1996.
Come to think of it, it should be 1995-1996. Sorry.

6. will a ball rebound higher on a hard surface than a soft surface?
Hard surface, as the soft surface will absorb some of the impact of the bouncing ball, causing the rebounded ball to bounce up lower.

7. if 1 battery is used up, is the circuit open?
A used up battery will become an electrical conductor.

8. do we need to know the functions of sap and vacuole. if we do, what are the functions?
Sap and vacuole are not in the syllabus but it's important to know that animal cell has vacuoles too just that they're numerous and much smaller. Plant's vacuole is known as sap vacuole or central vacuole. I discourage you from writing that as a difference as some pupils wrote that animal cells do not have vacuole, which is a wrong fact.

9. in the syllables, what are we supposed to know about a greenhouse?
You're supposed to know that any form of greenhouse effect refers to the air being trapped in an enclosed area (usually transparent) traps heat from the sun, causing the temperature in the enclosed area to be higher than its surroundings.

10. i am still not quite sure about gravity. is it correct to say that:

- when air resistance is the same, no matter what the height, objects of the same mass will drop at the same time but the impact of the higher one will be greater. but if both are of different masses but same height, both will still fall at the same time.
This is true when air resistance is the same. Say for the most confusing feather and plastic bag. Let's assume both are of the different mass but have the same air resistance, they'll reach the ground at the same time. In primary school, usually questions assume that there are no air resistance, eg the ping pong ball and dent in the flour question. However, once it involves a light object like paper or feather, you must know that they have air resistance.

- when parachutes are involved, the heavier will fall down first when both are at same height. also, when both are of same mass but different heights, the one higher will fall down later.
Correct. Take note that air resistance in parachute comes in the form of "area of parachute". So if air resistance is the same, the size of the parachute must be the same. Then the heavier object will reach the ground earlier.

Michelle, could you post the questions you asked during the chat?

posted by Allan at 10:38 PM | 0 Comments

; 6H's Questions

Kieron:

There is a circuit, in the circuit, there is a battery and 2 bulbs in a series arrangement. If one of the bulb fuses, will the other bulb still light up? If your answer is no, I would like to know the reason as the metal casing of the fused bulb can still act as a conductor for the electricity to flow around it and close the circuit.

If one of the wires is at the metal tip and the bulb fuses, it becomes an open circuit. However, if the metal casing is linked to two wires, it is an electrical conductor regardless of whether it has fused.

Glennis:

As for question number 15 of this paper, why does Bulb P lights up? I thought when Q fuses, P will fuse as well since they're of series arrangement?

http://www.misskoh.info/07/primary6-rosyth-science.pdf
Good question. This question is testing whether you know metal casing of bulb is a conductor of electricity. Bulb Q wasn't connected at the metal tip but at the metal casing by 2 wires. So whether it fuses or not, electricity will flow through its metal casing.

http://www.misskoh.info/07/primary6-nanyang-science.pdf

For question 10 of this paper, why is the answer 3???
First of all, the changes in volume of water when it changes state is out of syllabus. When water freeze, its volume increases. That's why ice will pop out of your ice tray. When ice melts, volume expands back. Ans is 4, not 3

And question 22, why is the answer not 2?
Hot air can move things but in this case, this toy doesn't use hot air, it uses our strong blow to move the toy. So, it is a push from the breath we blow and it can overcome the weight of the ball. Moreover, they wrote about the ball gets heated and rise, not hot air pushing it in (2). We're mammals, we're warm blooded but we don't rise hehe

Question 25, is bronze a magnetic material? What about mercury and alcoholic?
None of the above. Only steel and iron are magnetic in your syllabus. The other magnetic materials are cobalt and nickel.

As for question 26. How to see which switches are needed to be close? Are the switches in parallel same as those in series?
Arrangement of switches does not matter but the location matters as it can make a whole circuit or part of a circuit open. For this question, test all options and check whether the current from the batteries can flow from the positive terminal to the negative one.
(1) A, B, D --> 2 bulbs light up
(2) A,B,C,D --> Still same 2 bulbs light up or there might be a short circuit skipping 1 of the bulbs.
(3) A,B,D,E --> all bulbs
(4) A,B,C,D,E --> all bulbs
I would say both 1 and 2 are correct but 1 is the best of all answers.

Explain question 27 and 28. Why is the answer for 28 not 2?
For 27, firstly, you can't compare things of different units, so (2) and (3) are out. Light energy converts to heat energy, so (4) is out. Light energy converts to heat energy in water (a matter) while vibrating fork emits sound energy to convert to KE of water (matter), so (1) is the answer.
For 28, it's a solar cooker, so it's making use of heat energy from the sun to cook something. (1) and (3) have nothing to do with energy, so they're out. (2) is reflecting the light energy away, so heat energy is reflected too, how to cook?? (4) channels the sun's heat energy into the beaker of water to cook whatever's in the water.

In view of the answer for question 30, does it mean that if the magnet is further from the bottom magnet, it is stronger? But i thought the bottom one is suppose to be stronger? Since they have the same mass, why isn't the answer 4?
The further the magnets, the stronger the force of repulsion PROVIDED you did not change the bottom magnet or the top magnet for comparison. So, you can conclude that A is stronger than C based on set-ups 2 and 3 (same bottom magnet, D). B is stronger than D (same top magnet in set-ups 1 and 3). So, only 2 conclusions on strengths of magnets can be drawn.

-For dispersal of seeds, how can i know that they are dispersed by animals? Is it because they crowd together? Wait, crowding together is for splitting or..??
By animals, the seeds are randomly scattered all over usually.

-Is nuclear a renewable source of energy?
Can be renewable but mostly non-renewable but nuclear energy is out of syllabus.

-Which comes first--- pollination, fertilisation, germination, seed dispersal, development, flower reproduction?
None as plant life follows a cycle. It's like asking whether the egg or the chicken existed first. Say i start from seed germination, it develops into a plant with flower, then flower gets pollinated and becomes fruit. Fruit has seed for dispersal. Seed germinates and this cycle continues.

-If 3 seeds are placed on damp cotton wool in a beaker and the beaker is placed in a cardboard box, will the seeds still be able to germinate?
Yes. it doesn't need light to germinate, just 3 conditions: water, oxygen, warmth (no need sunlight)

- If 2 groups of fruits are edible and are eaten by animals, but have a different way of how their seeds are scattered, how to differentiate them?

e.g. mango and papaya= group 1. inedible seeds

Cucumber and tomato = group 2. small and edible seeds

-Is it true that when there is more water, more heat will be transferred?
Depends on the surrounding. Heat travels more if the temperature difference is wider but water is a poor conductor of heat.

Is it true that air is a better conductor of heat than water? Air is better than water in conducting heat.

If its true, what about electricity? Which is better? Water conducts electricity (not pure water though), air does not conduct electricity.

PSLE Booklet, page 55, question 8, I thought when GPE is highest at the two ends, it will decrease when the boy touches the ground? Why did the potential energy plotted at the graph increase instead of decreasing???
I don't have the PSLE booklet with me now. But if it is the swing question, GPE is zero when boy touches the ground as height from ground is zero. Did you read the answer wrongly?

PSLE booklet, specimen paper, question 22. I thought height from the ground at A is higher than B, GPE should increase right? Why is the answer 2 not 3??
Is it the skater question? At a higher height, GPE ought to be higher. You're right. Wish i have the book with me.

-Does all young of an animal/ insect that go through the 3-stage life cycle looks like its parents?
For insects, most of them. At least I've yet to see one that doesn't look like parent.

- Gravity is dependent on mass only right? Does it depend on height?
Force of gravity is dependent on mass. It does not depend on height. Just remember, is it harder to walk on the 50th floor? It's just as easy as walking on the 1st floor, so force of gravity did not increase as you go higher or lower. But GPE is dependent on height and remember that GPE is energy waiting to convert to other energy, usually KE.

posted by Allan at 10:33 PM | 0 Comments

; Circulatory System

Purpose of circulatory system
- To transport oxygen and digested food to all parts of the body.
- To transport carbon dioxide and other waste materials away from all parts of the body.
- To ensure gas exchange is carried out at the lungs
- To allow respiration to take place at different parts of the body as oxygen is required by cells to convert food to energy.

How does it work?
- Heart is a muscle that pumps the blood to all parts of the body via blood vessels.
- Blood carries oxygen from the lungs to the heart and from the heart to other parts of the body for respiration to take place.
- Respiration requires oxygen to convert food to energy at different parts of the body. At the same time, carbon dioxide and water are produced by different parts of the body.
- Blood will transport carbon dioxide away from the other parts of the body back to the heart.
- The heart then sends the blood low in oxygen to the lungs for gas exchange to be carried out.

When exercising
- Heart pumps blood faster in order to deliver more oxygen to different parts of the body for respiration to be carried out faster.
- During exercising, respiration speeds up, more oxygen is used to convert food to energy at different parts of the body.
- At the same time, more carbon dioxide and water are produced by different parts of the body.
- The blood then hurriedly transport them to the heart and then from the heart to the lungs for gas exchange.

Regards,
Mr Wan

posted by Allan at 5:46 PM | 0 Comments

Wednesday, October 6, 2010 ; Psle...

Yo 6 Diligence!! Just try your very best and sleep early the night before!! Don't stress yourself too much. And just relax and do your paper well :D Hope you are ready for this battle!!

posted by Zi Jun at 4:17 PM | 0 Comments

; Answers Jia Dao...

Yo Guys.. here are the CORRECT answer for some in paper 2 Practice paper 9

Q 5 should be 36cm not 38 cm

Q 9 A is $(6m+516)

posted by Zi Jun at 3:59 PM | 0 Comments

Friday, October 1, 2010 ; Karina's request in 5B (6H)

This is a request from Karina of 6H:

Q33c) I would like to ask for the answer to Q33. (c) as it is not stated in the answer key.

Location X is a in a cold place. The bottle has earlier lost heat to the colder environment and becomes cold. As glass is a poor conductor of heat, it gains heat slowly when the environment starts to get warm. So the warmer water vapour condenses on the colder glass.

Note: If X is in a warm place, the water vapour in the bottle would condense on the inner glass, forming water droplets inside as glass being a poor conductor of heat causes the trapped warm air in the bottle to lose heat very slowly to the environment. As a result, the warm air inside the bottle will condense on the colder inner surface of the glass.

Regards,
Mr Wan

posted by Allan at 11:12 PM | 0 Comments

; Michelle's Questions

These are questions Michelle post and my answers are in red.

6A

Q7) Each ocean zone has a different amount of light. When you mean shadow, where is the shadow? if fish is at twilight zone, is the shadow as the surface of the dark zone?
I meant a blurry image of the fish. It's not really a shadow, sorry. There will be no shadow in a dark zone unless it's light from organisms.

Q10) The question wrote "In the above set-ups, A and B, bubbles of gas were seen rising in the water when the switches were turned on" What does it mean "bubbles"? How does it form?
Actually, the process is called electrolysis. It is a method to separate different elements like iron, calcium, oxygen, hydrogen, etc, in a liquid using electricity. The bubbles formed are actually the hydrogen and oxygen moving towards the two metal plates called electrodes. They move because of different charges (positive and negative) on the 2 electrodes. This is totally out of the syllabus. It's a very difficult sec 3 science concept. Just take the bubbles as "substances" removed from the solutions. In this case, it's hydrogen and oxygen.

Q23) I don't understand why is the answer 4 and not 2. (2) Herbivore (4) Scavenger?
It's actually not a scavenger but a detritivore. Herbivore is more for organism feeding on living plants or parts of plants. Scavenger feeds on corpse not killed by itself eg vulture. Detritivore feed on dead plants eg earthworm. The so-called best of the worst answer is (4). I think I'll accept (2) too as it involves plants.

Q30) When Pham put several marbles into the can, did he take out the can then put it in or just put in on top of the can? And how does it affect?
Whether he put it in or on top will not affect the total mass. So the force of gravity acting on the can has increased, pulling the can further downwards and caused the water level to rise as the can occupies space.

7A

Q7) Is it true that if there is not cell wall, it is definitely an animal cell?
Not true as yeast has cell wall too. Given the regular shape of both cells C and D, they are plant cells.

? ? ? ?What are parts of the fungi cell? Is is like animals?
Fungi cell is like an animal cell but with a cell wall. This is the basic shape of a yeast cell. Some fungi cell has large vacuole too. But it's not in your syllabus, neither is the shape of yeast cell.

Q9) To a certain extent, amount of carbon dioxide and light affects rate of photosynthesis. Does amount of water affect too?
Yes, but there's a limit to how much a plant can photosynthesise given a high amount of light. For water, the rate of photosynthesis also increases with water till a certain extent. Too much water can cause roots to start rotting.

Q17) You wrote "The more the spring is compressed, the higher the metal ball goes when the spring is released". When it is released, is it all EPE convert to KE, then the KE would convert to GPE when it goes higher? Does it mean that when it just started to move, the KE is highest?
KE is very high but not the highest. Both the GPE and KE get their energy converted from EPE. When the ball's going to hit the ground, then it's the highest. This is because GPE has converted to KE as the ball approaches the ground.

Q19) What caused the iron fillings to stay? <- asked by Yun LIng
Iron filings are in fine powder form. It's like asking how come pepper can get stuck at the test tube or how come dust gets stuck on the inside of the test tube.

Q23) Could temperature be above boiling point? Like ice below freezing point?
Yes, steam can be above 100 degree Celsius as it gains more heat.

Q26) The reason you wrote what strange. I think it is not because of whether nearest to water to decide which is dispersed by water, which is dispersed by animal. Could I write: Because if A is dispersed by water, the children plant should locate lower that A as the flow of river is downwards, and it could not travel upwards, but the second picture shows that the children plant A locates above adult plant A, so it is not likely to be dispersed by water.
I was thinking of possible A upstream. It is mainly because of how A is distributed along the banks of the river that makes it a very natural choice for dispersal by water.

Q27) Does wax and cork gains heat from electric heater too??
Not directly. More of wax gains heat from the metal plate and cork gains heat from the wax.

? ? ? ? ?Is it because of air that allows heat transfer? What allows heat transfer then?
Heat transfers through radiation, convection and conduction. You only need to know conduction whereby heat flows from a warmer object to a colder one.

Q29) If surface Y has more friction, then why take longer time to travel before it stops, even though it travels a shorter distance?
My answer is actually longer distance for X than Y, so X travels a longer distance. Y takes a longer time to travel a fixed distance, not stopping distance. Given a fixed time, say 3 seconds, X will travel further than Y, so the friction between trolley and surface X is lesser.

PSLE Science Q44) The ball should not travel further but travels to a lower height. I don't understand.?
Given a lower force, an object couldn't have travelled further. Furthermore, the height should also reduce. You cannot draw the ball beyond the horizontal distance of the original ball.

Others

Q1) A smooth surface and a similar surface with ups and downs along the way. Why the second surface cause more friction?
It's bumpy and rough, so increases friction.

Q2) When it's dark, our eyes adapts to the changes and then we can see more clearly. Why? And when a light is opened, why do our eyes feel uncomfortable?
Our pupil (in eye) has become bigger in the dark to try to absorb all possible light for us to see. To switch on light suddenly will allow a large amount of light to enter our eyes before the pupil becomes smaller. The sudden influx of light causes us to be "blinded" for a while.

Q3) Respiration: Oxygen+ Food -> Energy + Carbon Dioxide + Water

? ? ? ?Is it that after respiration, heat energy is then converted?
Heat energy is also converted from chemical potential energy. However, not all organisms can use food to convert to energy, eg crocodile.

Q4) Mangrove plants have breathing roots that stick out to the mud. These roots have tiny openings for absorbing oxygen from the air.

? ? ? ?Does leaves exchange gas too?
You mean roots? Yes, the roots do.

? ? ? ?Does other parts of the plant exchange gas too, besides leaves? (to all plants)
Yes, actually all parts of the plant, like roots and stem, do take in oxygen to respire but we focus mainly on leaves having gas exchange.

? ? ? ?Is there a gas transporing tube to transport oxygen to the leaves?
Yes, water-carrying tubes carry dissolved oxygen as well but that's not important.

Q5) Cactus has spines instead of leaves to cut down water loss through transpiration. How?
Spines are very tinny leaves. Small leaves mean small stomata, do less water loss through leaves.

Q6) Experiment shown that when salt is added to ice, the temperature decreased, but you cannot conclude that the meling point decrease, can you?
Melting point as based the change of state of matter from solid to liquid.

Q7) If a food e.g. bread is placed in the fridge and it moulds, how will spores land?
Spores are everywhere, just like dust. It's a matter of whether they have good conditions to grow.

Q8) The air we breathe out include water vapour. Where does it come from? And when the air we breathe goes to the lungs, ?does all air get taken in?
It comes from respiration at cells to use oxygen to covert food to energy. Water and carbon dioxide are produced during respiration.

Q9) How would amount of sunlight affect rate of transpiration?
The warmer it is, the higher the rate of transpiration.

Q10) "Electricity always tries to find the easiest path to the ground". What does it mean?
Did I write that? I don't know what it means too. I must have meant other things for "ground". Short circuit is not in the syllabus.

Q11) What is static electricity? Is it in syllabus?
Nope. It's better not to know static electricity.

Q12) (Plants) Why would rate of respiration decrease during the day? I thought more activities (Photosynthesis), higher rate of respiration?
I agree with you too. Did I write wrongly again?

Regards,
Mr Wan

posted by Allan at 11:03 PM | 0 Comments

; Yun Ling's Question and Answer

My answers are in red while her questions are in green or black.

When 2 batteries are in parallel, the amount of energy used for both batteries are the same, meaning both will be drained at the same time, not one at a time. Batteries in series makes the bulbs brighter. They're supplying more electrical energy but they might cause the bulbs to fuse if the electrical energy is too high.

but when 5 batteries are in parallel, you take out 4, won't there be a difference? But i always write that there will be no difference as i thought only drain from one battery.

If there isn't a difference when 4 are taken out, does that mean that they all add up to the electricity of one battery?

They last longer when they're in parallel. In terms of electrical energy provided at that point of use, there's no difference from 1 battery.

When do we use "-->" and "+" for energy conversion?

for example in the experiment where we put a paper ball on the spoon and bend the spoon. When bent further, the paper ball travels further.

so its:

EPE of the plastic spoon --> KE of plastic spoon + KE of paper ball

Why is it ''KE of plastic spoon+KE of paper ball'' instead of ''KE of plastic spoon-->KE of paper ball" Doesn't that make more sense as the KE of plastic spoon in the one that causes the paper ball to move?

The use of "+" and "-->" are not exactly that precise. Like you described, the KE of the paper ball can come from the KE of the plastic spoon. But then, the plastic spoon and the paper ball both move at the same time which was triggered by the EPE of the spoon. It can be both --> and + in this scenario. PSLE is more focused on the use of "-->" than "+" unless electricity is involved which is always "some energy+ heat energy".

Nuclear power plant
advantages: reduce its reliance on oil and natural gas, more environmentally friendly... etc.
disadvantages: no space to store spent fuel, highest construction cost. We have to know the energy conversions but the advantages and disadvantages?
Plus, is nuclear power plant in our syllabus? Cas i still don't get how it works :l sorry.

You're not needed to know how nuclear works or the advantages and disadvantages of all power stations but I'd say it is very helpful to know as they can provide information as ask about it. Anyway, just for knowledge, nuclear energy is a form of potential energy. So it goes like this

nuclear (potential) energy --> heat energy --> KE of air (boiling of water to steam) --> KE of turbine --> electrical energy

For decomposers, they break down dead materials to simple or simpler substances?

Simpler substances.

10) Why is there secondary consumers? I don't understand how come the can't be called tertiary consumers.
Primary consumers definitely must feed on food consumers, tertiary must feed on a food consumer. So what is the definition of secondary consumer, what is the difference between secondary consumer and tertiary consumers?

Primary consumers get energy from food producers. Secondary consumers are just consumers that get energy from primary consumers and tertiary consumers get energy from secondary consumers. Actually, they're not in your syllabus. It's just good to know how food web organisms are described as some of you read widely beyond the textbooks.

New Questions:

1) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/a1d5550a35132f7d768a9cd73d70318e/mcq_id/19823
A: Most birds lay eggs.
B: All birds care carnivorous.
C: Birds are warm-blooded.
D: Birds have beaks and feathers.
Isn't A,C,D all true? don't all birds lay eggs?
Yup, all birds lay eggs. Hence A is false because of the word "most".

2) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/1ae7eed744e6441bcc3e2d1bf8dce67a/qn_id/18171
is this in syllabus? I dont understand why its fern
Neither do I. I know nothing about fern cells. This is not in syllabus. I don't know the answer myself :P

3) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/1ae7eed744e6441bcc3e2d1bf8dce67a/qn_id/17970
cell wall, cell membrane, cytoplasm, i can't remember which one is semi-permeable... What is the cell membrane and cell wall for? i know that cell wall is for regular shape.
Cell wall is fully permeable while cell membrane is semi-permeable. Cytoplasm just contains whatever cell membrane allows in.
Cell membrane controls substances in and out of the cell. Cell wall gives support to the cell and the cell a regular shape.

4) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/a1d5550a35132f7d768a9cd73d70318e/mcq_id/19763
which part of the plant contains chlorophyll? i know the roots don't, flowers don't. But the stem does, doesn't it?
The stem of cactus do but most stems do not despite being green.

5) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/a1d5550a35132f7d768a9cd73d70318e/mcq_id/19764
A: Both X and Y are single-celled organisms.
B: Budding has taken place in both organisms.
C: The cells in both organisms X and Y have been fertilised.
D: Only one parent cell is required to produce 2 daughter cells.

A only (answer)
D only
A and D only
B and C only

Why isn't D correct?
For question on budding, the bigger cell after budding for Organism Y is the parent cell while the smaller one is the daughter cell, so D is wrong. This, however, is in your brother's syllabus, not yours.

6) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/a1d5550a35132f7d768a9cd73d70318e/mcq_id/20152
Just to clarify:
Ishak: From P to Q, there is an increase in height as the number of cells in the body increases.
Jena: From Q to R, there is no change in height because there is no cell division.
My answer: Cell division to replace dead or damaged cells, not for growth
Kathy: There is an increase in height from P to Q as the size of the cells in the body grows bigger.
My Answer: Increase in height is because there are more cells, but all cells do not grow

Are my answers correct? Yes, you're correct. Cells do not grow bigger. They grow in number, not size.

7) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/a1d5550a35132f7d768a9cd73d70318e/mcq_id/19824
I dont get this, what are they classifying it as?
By habitat, X is rotting log while Y is tree.

8) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/1ae7eed744e6441bcc3e2d1bf8dce67a/qn_id/17987
Isn't this by body covering? then why lizard with seahorse?
Reptiles are covered by scales, as of fish. Reptile is not in your syllabus.

9) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/1ae7eed744e6441bcc3e2d1bf8dce67a/qn_id/17990
C: Once alive
D: Never alive
for part (b), you once told us that there was no such classification as once alive and never alive, but we learnt it that way in P3?
Really? I've been told 6 years ago NEVER to teach like that. Please ignore such questions. :)

10) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/1ae7eed744e6441bcc3e2d1bf8dce67a/qn_id/18157
(b) I choose material for paper as paper is light so it can float on the water but it absorb water, so after some time, it will be heavy and sink into the water.
Paper floats because wood floats (ignore absorbing water). True or false?
True. This is in the syllabus.

11) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/a1d5550a35132f7d768a9cd73d70318e/mcq_id/20056
aluminium is a poor conductor of heat? isn't it metal? :l
My answer is (4), all of the above. Aluminium is a good conductor of heat and it is important in all the 3 objects.
Aluminium drink can: Loses heat to cold air in fridge so drink can be cold
Foil and food container: Gain heat quickly from heat in oven so as to bake/heat up food

12) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/1ae7eed744e6441bcc3e2d1bf8dce67a/qn_id/18155
shouldn't Q be an insulator of electricity?
Yes, Q is insulator of electricity. I think there's an error in the answer key. It has happened in oldschool.com.sg before.

13) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/a1d5550a35132f7d768a9cd73d70318e/mcq_id/19849
Its A and C right?
because theres the metal casing around that conducts electricity
Correct. IThey're circuits A and C.

14) Which one of the following is true?

A: all materials will absorb some light when light passes through
B: The ability of light to pass through can be further classified into 3 categories
C: for opaque objects, all light cannot pass through and is all reflected away
D: several pieces of translucent materials stacked together may become opaque altogether

ANS: A,B and D

A: Yes, even clear glass absorbs light, hence it can gain heat from light energy.
B: Yes, transparent, translucent, opaque
C: No, if light is completely reflected, it is a perfect mirror. If an object is green, green light is reflected into our eyes. The rest are absorbed. Bear in mind, green can come in many shades, so it's not just green reflected. This is not in the syllabus.
D: Yes, there's a PSLE Booklet question on this concept.

Other New Questions
1) Place a plant in blue coloured water and the stems and leaves will turn blue.
Why is it we always just write the flowers, we never do write that the stem turns blue as well.
Water-carrying tubes are inside the stem, so usually stems do not change colour easily.

as for this experiment they have one balsam plant in blue coloured water.
Aim: to find out if __Changed variable__ affects ___results____
So in this case the changed variable is the blue dye? results is stem and leaves turn blue?
But there isnt actually a changed variable is there? its only one set-up..
The aim can be anything. It could be whether balsam plant takes in blue water. It could be whether plants take in blue water. It could be whether plants take in coloured water. I mean the changed variable could be anything unless they provide one more set-up for comparison. Otherwise, they would have to accept any possible answer. Results could be leaves and flowers turn blue, unlikely to be stem. Flowers definitely.

Then what about control?
What is the purpose of the control and in the first place how should the control set-up be like?
Control would be balsam in clear water to check if the leaves and flowers turn blue without coloured water. I mean to put it stupidly, what if balsam turns blue without the use of blue colour? (Although we know it's not possible)

2) Then if there are two test tubes and both with a straw through the stopper, in the test tube one set-up has limewater, the other clear water
the aim is to find out if carbon dioxide turns limewater chalky, so shouldn't the other set up have nothing instead of water?
No. The use of limewater is to test for carbon dioxide. The second set-up is wrongly set-up. You should set up another one that uses limewater but for one set-up, carbon dioxide is blown into the straw. For the other, no blowing.

3) Does every experiment need a control? can a experiment only have one set-up?
Experiment may not need a control. An experiment might have only 1 set-up. For example, plant with 1 leaf wrapped with black paper but the rest not wrapped.

4) a sealed tank with water, fish and hydrilla
to find out: do the hydrilla and fish provide the gases and food for each other to survive?
is that even a proper experiment? there's no changed variable, no control, no comparism...
I'd say the aim is to find out if they can survive with each others' presence. In a way, it's a yes-no experiment. It's proper but it's a weird experiment.

5) Exhaled air:
1)contains more carbon dioxide than that of inhaled air (this is because inhaled in 0.03%, exhaled is 4%) <-- Not required to know exhaled %
2) contains water vapour
3) warmer than inhaled air
4) exhaled air 78% nitrogen 18% oxygen 4% carbon dioxide <-- Not required to know %

however, another workshee't's answer wrote:

The air we breathe in and out contains both oxygen and carbon dioxide.
The difference is:
1) we breathe in more oxygen than carbon dioxide (because 21% oxygen, 0.03% carbon dioxide?) <-- Required to know %
2) we breathe out more carbon dioxide than oxygen <-- this is wrong
Exhaled air contains more water vapour than inhaled air because of respiration

6) How does salt affect the boling points and freezing points of water?
I know it decreases the temperature of ice, but does it raise boiling point?
Salt reduces freezing point and raises boiling point but this is not in syllabus

7) 1000cm3 of air is drawn out from a hole on the cover of an 800cm3 glass cylinder. The hole was immediately sealed after the air was drawn out. What is the volume of air in the glass cylinder after 1000cm3 of air has been drawn out?
The answer is 800cm3
But how do we know that so much air is compressed in the cylinder? after removing 100ocm3 from a 800cm3 container how is there still 800cm3 left? Isnt that a little too much? or on the other hand there may be more, just that its compressed, do maybe another1000cm3 still can be drawn out?
Actually, there's no right and wrong answer as air has no definite volume. In a way, as long as there's air, the volume of air is the same as its container regardless of how much is pumped in or out.

8) When do we use ''it takes up space'' and when ''it has a definite volume'' when describing?
All matter has mass, so they take up space. Air is the only matter without definite volume. That's the main difference between these 2 descriptions.

Like for example there's a jar filled with water, when stones are added in, the water overflows. Which reason is it? I thought we should probably write both. Because if i write ''it takes up space'', its like all matter takes up space, so it doesn't really explain, but when i add in ''it has a definite volume'' it means that it cannot be compressed so it will take up that space and there will be no space for the water... something like that.

So can i write both? Some of the answer sheets wrote takes up space, some wrote has a definite volume. both were describing solids.
Yes, you can write both. I'd say it's safer to write both. I might even write that water cannot be compressed, so it overflows.
My Answer: Stones take up space and has definite volume. When stones are added, the same volume of water is displaced out of the jar as both have a definite volume and cannot be compressed.

Regards,
Mr Wan

posted by Allan at 10:51 PM | 0 Comments

Thursday, September 30, 2010 ; 7A

Dear 6D pupils,

There are some problems with either the answer on the sheet given by Mr. Wan or the diagram:

Q3) Answer should be: 3

Q9) Answer should be: 1

Q19) Answer should be: 3

Explanation given are all correct.

For Question 10, there should be a foil covering test tube B. If not, A and B would be the same. Your answer should be different after reading this.

I hope it helps. Mr. Wan said that the 2 hardest questions are question 12 and 30 if I'm not wrong.

Thank you

Michelle

posted by 6 Diligence at 7:46 PM | 0 Comments

Wednesday, September 29, 2010 ; PSLE IS COMMING!!!

Yo 6 Diligence!!!! PSLE IS COMING. Dun worry, i am sure we can do it!! Good luck to you and i hope everyone could go to your desired Secondary School!!! Two Weeks later, wonder how would everyone look like:) Zombies!! Dark eye circles... LOL Anyway, wish you best of luck! Dun stress your self so much. JUST DO YOUR BEST!!!!

All the best,

Zi Jun

posted by Zi Jun at 3:56 PM | 0 Comments

Friday, September 17, 2010 ; Questions you asked

Dear pupils,

Here's a list of questions asked by various students of 6D.

If it was a ball, then the lane goes up and down, at which point would the ball have the highest kinetic energy?

As long as the lane hasn't ended, the lowest point has the highest KE.

What if the lowest point is the point that is going upwards, like a roller coaster going up and down, what if the lowest point is going up?

If it goes up, KE would have converted to GPE, hence lower KE. So, the lowest point still has the highest KE. At the lowest point before heading up, height from the ground is the lowest. So, there is very very little GPE. That means the rest of the total energy is KE. It has not gone up yet and so GPE is still very low. KE is usually the opposite of GPE. So the lowest point has the lowest GPE and the highest KE.

In a river, what causes the water to be more acidic or have more alkaline in it?

Acidity of water is caused by pollutants. Salt can cause water to be alkali. But these are not in your syllabus, except acid rain. Burning of fuel can cause rain to become acidic and the acid rain can wash into rivers.

When liquid turns to solid, will it increase in mass? Will the volume change too? (Not in syllabus)

For the liquid become solid question, it's out of syllabus to know volume.

For your knowledge, density measures the ability to float and density = mass/volume

So when density decreases (float), volume increases. For water to become ice, the density of ice must be lower than water to float on water. So the volume of ice is higher than water in order for ice to have a lower density. Remember that mass remains unchanged.

However, for most other liquid, volume will increase when they freeze and so when they become solid, their density increases and causes it to sink.

If you put soil in a container, then some water on top, could the air between the soil escape?

There will always be space between the soil particles. Just that, when you add water to soil, clayey soil in particular, the soil particles stick together and there is very little space for air to escape from the soil.

For a setup where they hang a rubber band on a stand and add weights on it, can we can they the pull of the weights overcomes the push of the rubber bands? because for every pull there is a push. But i don't get how the rubber bands are giving the weights a push... Isn't it just elastic potential energy or something?

Gravity is the pull acting on the weights and the rubber band. At the same time, elastic spring force from the spring is pulling the weights back. As the spring is stretched, it increases in elastic potential energy. EPE is not a force. A high EPE can convert to a high KE, which can result in higher impact (force).

And for water plants, is it true that they will die on land as they can only take in dissolved oxygen during respiration? And water plants takes in dissolved oxygen, do they also take in dissolved carbon dioxide during photosynthesis and give out dissolved carbon dioxide during respiration?

Water plants take in dissolved carbon dioxide and gives out dissolved oxygen during photosynthesis. They take in dissolved oxygen only as part of respiration but respiration is a 24-hour process.

And since only water vapour can condense, isn't it wrong to say that ''tiny water droplets have formed (condensed) on the outside of the glass"? Because that was the answer given in my assesment book. I thought it should have been "Water vapour condensed on the outside of the glass to form tiny water droplets"

It's wrong to say water droplets have condensed but correct to say that water droplets have formed or "have formed after condensation".

So when the plants transpire is it like humans,--water is a by product of respiration? And during transipration it is losing water vapour but why is ''lost water'' accepted?

Unlike breathing which focuses on the gas exchange, transpiration focuses on the loss of water vapour from stomata. You're right to relate it to respiration as respiration takes place in plant cells, carbon dioxide and water are by-products of respiration and these will be released in gaseous form from the stomata. Just that the process of water vapour exiting the stomata is known as transpiration. The plant "lost water" in the form of gas through its leaves. This is a generally accepted term.

Is it true that gravity is the same regardless of height from the ground? Is it different from the concept on the heavier the mass of the object, the higher the gravity acting on it?

On gravity, both are true. Gravity is the same regardless of height because our mass does not increase as we climb higher and higher

There is a mathematical way of remembering gravity.

Gravity is a force. The mathematical formula for it is Force = mass x acceleration, F = ma
where Force is gravitational force, mass is mass of an object, acceleration is the measure of change of speed of a falling object and acceleration is the same for all objects on Earth if the object has no air resistance.

Effectively, gravity is only affected by mass and air resistance.

Height comes in when you deal with GPE as GPE = mass x acceleration of free fall x height from ground. or GPE = mgh

That's how I remember gravity as I'm more mathematical than scientific.

For friction, is it a pull or push?

Friction opposes motion. We usually push ourselves forward, so friction is pushing against us.

Do the plants xylem and phloem tube run through the fruit and flower?

Yes, they do. The cell part vacuole is made up of plant sap and primarily contains water. This is, however, not in the syllabus.

When soil erosion blows the top layer of soil away, why does the land become dry and hard and impossible to grow new plants on?

Topsoil are rich in nutrients and soil particles that are not eroded are either larger in size (pebble or sand like) or of a clayey nature. Hence without the nutrient-rich topsoil, the remaining soil is not suitable for plant growth but there'll still be highly adaptable plant that grows on them. With the remaining larger soil particles, it's easier for water to trickle deeper into ground water or evaporation on the surface to take place.

You're not required to describe why the soil is dry.

Are we required to know the different types of veins and the different things in blood like platelets and plasma?

Absolutely not. You only need to know what the blood carries, from where, and to where. Only 4 things: digested food, oxygen, carbon dioxide, waste material.

How is it there can be 2 pushed and 2 pulls. I thought theres this law saying for every pull there will be a push?

It's a matter of perspective. Let's say we said that gravity is pulling us. Actually the direction of the force or arrow is pointing away from us. To gravity, it is pulling us. But to us, we're pushing the ground. So gravity's pull is same as us pushing the ground.

While gravity is pulling us to the ground, to gravity, we're pushing the ground too.

For friction, it is a force that travels towards us in terms of direction. So, we feel a pull from friction but to friction, it is pushing us.

It's not that important to differentiate push and pull, more important to know what the directions of the forces are when they act on objects. Eg, gravity is always pointing towards the ground and friction is always pointing the opposite direction of motion. However, direction of forces, sadly, is not in primary school syllabus. Yet, it makes people understand how force works better.

You'll learn more when you study science in sec 3.

If you take two cubes, one made of sponge and one made of wood, of the same size, and throw them on the same wall at a equal distance, is it true that wood will have more KE when it hits? I was thinking that the sponge would absorb the impact so theres less KE. But i didn't think it made sense cas KE is affected by mass and speed. Or Maybe its because the sponge and wood have different masses?

Absolutely right! Given the same volume, sponge definitely has much lower mass than wood. If you apply the same force to throw it, definitely the KE of sponge is much lower than KE of wood as its mass is substantially lower. You need not consider absorption of impact for this case.

Look at absorption of impact when they compare soft and hard grounds. If it's smooth and rough grounds, they're testing on friction, not impact.

posted by Allan at 7:50 PM | 0 Comments