- Six Diligence 2010

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: