PSLE 2012 - Science

[kwcllf]

Sun_2010:

Nebbermind:

Frictional force will be there as long as there is contact between 2 objects.


Frictional force is a function of the 'normal' force between the 2 surfaces, ie,

Ffriction = coefficient of friction x normal force acting on the surfaces.

Therefore it is only dependent on whether there is contact or not,or if coef = zero.

That formula is for the maximum frictional force . That is the value of the force above which if exerted on the object it will start to move.

Please refer to the problem 1a. I think it clearly states
http://web.mit.edu/8.01x/www/probsets/sol4.pdf

In the case of the object on the slope, yes there is a frictional force acting on it since it as it opposes the gravity acting on it.

But for the object on a flat surface, the normal force acts against the gravity. Frictional force doesn't come into play.

Thanks Sun_2010,

I think that clarify all the confusion the question throws up. As have been mentioned, I think we also have to think in context of P6 syllabus. I don't think the kids are expected to go into the topic on friction so \"chim\". What they have learnt is friction opposes an object that is being pushed. So, if stationary, then no friction. Very simplistic but that is to be expected for their level of underdtanding.

[RVHS]

Nebbermind:

Frictional force will be there as long as there is contact between 2 objects.


Frictional force is a function of the 'normal' force between the 2 surfaces, ie,

Ffriction = coefficient of friction x normal force acting on the surfaces.

Therefore it is only dependent on whether there is contact or not,or if coef = zero.

You misunderstood F here, here F friction refer to min force to move
If calculate base on above formula F =10N,
1) if push/pull force= 8N, friction force=8N
2) if push/pull force=0, friction force=0
3) if push/pull force=11N, friction force=10N
Pls refer sun_2010 post , he is correct

[AWSP]

One needs to be taught secondary school physics to know how ‘static’ friction would vary with applied force. and act only when there is applied force on the object.


At primary school level, I believe majority Science teachers in primary school (including my DD teacher) would have simply taught the students that ‘friction exists between surfaces, that’s why one needs to apply force to move the object to overcome friction, which can be reduced by lubricating the surface using oil and so on,’

Based on what is taught, students would have intepreted the question as ’ whether moving the object in different positions need to work against friction,’ and hence would choose all options.

I think the above needs to be highlighted to the examination board plus the question on tadpole, which I feel is also not a clear-cut question with no answer seems definite.

I wonder if there are more ‘open-ended’ questions like these that can be put togther for feedbacks to the exam board. Could you provide the details?

Unfortunately My DD could provide no further details other than saying that some questions look ‘weird’. I would like to see if there are more questions set like the ‘friction’ question…

(for haneyi, thanks for your reply to my question about ‘stigma’, the question would have been confusing if other options like ovules, ovaries, etc are also included among the other possible options to choose)

[ultimateschooler]

I say the paper is flawed.

[Mum of 3]

creamyhorror:

Mum of 3:

I do not disagree with the teacher's answers. However, if we consider this question from another angle, why is the difference in habitat an advantage when the frog and tadpole feed on different things in the first place?

Even if the tadpoles eat different things from the frogs, they'll still affect the overall food supply. Here's one possibility:


- Let's say both tadpoles and animal A eat animal B
- Let's say animal A is eaten by frogs
- So if tadpoles eat animal B, the population of animal A will be reduced
- Thus, frogs will have less of animal A to eat

So it makes sense for a species to geographically diversify and spread out, even if it eats different things in two stages of its life cycle.

Creamy Horror, I agree with your analysis but it is at a much higher level than what is within Pri 6 syllabus. From the thread, I gather that some of the students stated the advantage as \"there will be no competition for food\". Your analysis is based on food supply, not competition - a concept which Pri 6 students are taught (based on overcrowding).

[janet88]

Monsterparent:

Regarding the toad and tadpole question, is it acceptable if the student wrote \"so that the frog will not eat its own eggs and offsprings\"

My answer:
the frog does not look after its young, and not all the young will develop into adults as there are predators. by laying many eggs, this is to ensure continuity of its own kind.

[ultimateschooler]

Tadpole answers. Living in water offers better mobility as they have not developed legs. Also enables it protection from predators as it moves in numbers. This question

was posed in one test in Dd school last year.

[Nebbermind]

Sun


Didn't go thru the link but I guess should just ignore my earlier reply as I'm now not sure the context of the Qn!! :oops:

[Sun_2010]

Nebbermind:

Sun


Didn't go thru the link but I guess should just ignore my earlier reply as I'm now not sure the context of the Qn!! :oops:

Nehmind , Nebbermind .
Actually that was driving me up the wall too. almost all questions no one states the question. They just discuss the answers . And I am left figuring out the questions from their chatter. Or pester a colleague to ask her P6 DD about the Questions :oops:

As to whether this question is suitable or within the Primary science syllabus, remains to be seen.

[Sun_2010]

creamyhorror:

Unfortunately, all this is irrelevant from a P6 point of view. We don't know what MOE has decided to be an acceptable answer. Has anyone ever managed to ask MOE for clarification on an exam question?

Creamyhorror, Thanks for your posts. I like you take on the questions, logical explanations and the show a very good grasp on concepts. Hang around in the Science threads :please: . I will soon start needing more help in the next few years. When i will start wondering, how on earth I did my physics when i cant confidently answer seemingly simple questions.