Q&A - PSLE Science

[usaik]

Hi,


This question is from Nanyang 2011 SA1 paper.
http://i41.tinypic.com/6xxp8g.jpg\">

The answer given is 4.

I would like to know with regards to point B above; point B will make it is a more accurate experiment. what way would B make it a fair experiment? Appreciate your advice and sharing very much!

Thank you.

[Oldschool]

usaik:

Hi,


This question is from Nanyang 2011 SA1 paper.
http://i41.tinypic.com/6xxp8g.jpg\">

The answer given is 4.

I would like to know with regards to point B above; point B will make it is a more accurate experiment. what way would B make it a fair experiment? Appreciate your advice and sharing very much!

Thank you.

Hi,

For a plant to grow, it must have food. For a plant to produce food, it must be able to photosynthesize. For photosynthesis to take place, apart from chlorophyll, light and carbon dioxide must be present.

Placing one beaker in an enclosed box and one in the open, there are in fact two variables. One is the amount of light and the other is the amount of carbon dioxide.

Hence, the teacher suggested (B), put one more beaker in the open (so same amount of CO2) but at a dimly corner where only the amount of light varies.

Regards

[usaik]

Hi oldschool,


Thank you so much for your explanation.

Regards.

[Oldschool]

Goodluck8:

Hi, need help


Which required more force : pulling a load up a inclined plane or lifting the same load vertically up? Why?

Hi,

Generally, lifting would require more force as compared to inclined plane.

In fact, inclined plane is one of the ‘simple machine’ (other e.g. pulley etc) used to reduce the amount of force required to do work.

The forces acting a body resting on an inclined plane can be resolved (by secondary level onwards) to show that the amount of force needed to pull it up the ramp is less than weight of the body (acting by gravity).

On the comment that “pulling it up a inclined plane requires more force because it need to overcome gravity and frictional force but lifting it up requires to overcome the gravity only” @ http://www.kiasuparents.com/kiasu/forum/viewtopic.php?p=1001788#p1001788

I can only comment that who in the sane mind would employ an inclined plane which is so rough such that its frictional coefficient is so large that it actually impedes motion instead of assisting it.

Hence, used a smooth plane instead of a rough one if one want to make his/her life easier.

Regards

[gerberadaisy]

Hi all,


Can someone help with this question:

Why does the spectacles get misty when you emerge from an air-conditioned place such as a car?

Thanks!

[ngl2010]

Hi. Can someone help to explain why frictional force is not dependent on the size of surface area?


TIA

[sharonkhoo]

gerberadaisy:

Hi all,


Can someone help with this question:

Why does the spectacles get misty when you emerge from an air-conditioned place such as a car?

Thanks!

The aircon makes the lenses cooler than the air outside the car, so the water vapour in the air condenses on the cooler surfaces.

[gerberadaisy]

Thanks Simkhoo for your reply. I sort of figure out the answer already.

[Oldschool]

ngl2010:

Hi. Can someone help to explain why frictional force is not dependent on the size of surface area?


TIA

Hi,

Interesting that this is brought up in the primary section.

For primary level (or even to high school), it is sufficient/reasonable to consider that frictional force is not dependent on the size of the surface area. This (ambiguity) lies with the model used by early physicists in their investigation of friction where the early model limits that it is independent of area of contact. As such, based on the classic empirical model, frictional force is independent of surface area which is valid in many circumstances.

However, the phenomena – friction, is far more complex. In reality, the classic model is insufficient to explain many more examples.

Regards

[ngl2010]

Oldschool:

ngl2010:

Hi. Can someone help to explain why frictional force is not dependent on the size of surface area?


TIA

Hi,

Interesting that this is brought up in the primary section.

For primary level (or even to high school), it is sufficient/reasonable to consider that frictional force is not dependent on the size of the surface area. This (ambiguity) lies with the model used by early physicists in their investigation of friction where the early model limits that it is independent of area of contact. As such, based on the classic empirical model, frictional force is independent of surface area which is valid in many circumstances.

However, the phenomena – friction, is far more complex. In reality, the classic model is insufficient to explain many more examples.

Regards

Hi Oldschool. Thank you for the explanation. My son's teacher only stated that the frictional force is not dependent on the size of surface area. It was just my curiosity on why it is so because if my son plays on slide, he will slide faster if contact area is small. But maybe it is just my impression because I have never really timed it.