PSLE 2012 - Science

[kwcllf]

verykiasumummy:

i'm not proud to say that i have at least 10 sci guides at home... let me look thru all of them and give u all my conclusion since i have the resources available...

No wonder you call yourself \"verykiasumummy\"

[verykiasumummy]

kwcllf:

verykiasumummy:

i'm not proud to say that i have at least 10 sci guides at home... let me look thru all of them and give u all my conclusion since i have the resources available...

No wonder you call yourself \"verykiasumummy\"

sorry ya... it is 23 sci guides.... oh my god.... :yikes: :yikes: :yikes:

[mummy so kiasu]

verykiasumummy:

kwcllf:

[quote=\"verykiasumummy\"]i'm not proud to say that i have at least 10 sci guides at home... let me look thru all of them and give u all my conclusion since i have the resources available...

No wonder you call yourself \"verykiasumummy\"

sorry ya... it is 23 sci guides.... oh my god.... :yikes: :yikes: :yikes:[/quote]How did you manage to get so many? I think your range is wider than Popular bookstore.

[verykiasumummy]

mummy so kiasu:

How did you manage to get so many? I think your range is wider than Popular bookstore.

i bought over many yrs... bought all the different ones available everytime...

[verykiasumummy]

anyway my conclusion is, in all the guide books, the only mentioned about friction which is repeated is :


- friction is a contact force when 2 surfaces get in contact.
- friction has to be overcome to move stationary objects.

in 1 of them, it is stated that frictional force acts whenever 2 surfaces are in contact. eg when our fingers lift up an object, the friction between our fingers and the object helps to grip on it, so that it does not slip from our hands… (so does it show that friction exists even for stationary objects since the object is stationary in our hands?)

another guide says that :
if a body is in equilibrium (stationary), the frictional force is equal to the force of motion. (since there is no motion force, does it mean no friction?)

1 more guide says that :

friction exists whenever 2 surfaces come in contact. when we stand on the ground, the soles of our shoes interlock with the surface of the ground, so the friction grip on the ground so that we do not fall. (this again shows stationary object still has friction if not all things will fall.

[Nebbermind]

verykiasumummy:

anyway my conclusion is, in all the guide books, the only mentioned about friction which is repeated is :


- friction is a contact force when 2 surfaces get in contact.
- friction has to be overcome to move stationary objects.

in 1 of them, it is stated that frictional force acts whenever 2 surfaces are in contact. eg when our fingers lift up an object, the friction between our fingers and the object helps to grip on it, so that it does not slip from our hands.. (so does it show that friction exists even for stationary objects since the object is stationary in our hands?)

another guide says that :
if a body is in equilibrium (stationary), the frictional force is equal to the force of motion. (since there is no motion force, does it mean no friction?)

1 more guide says that :

friction exists whenever 2 surfaces come in contact. when we stand on the ground, the soles of our shoes interlock with the surface of the ground, so the friction grip on the ground so that we do not fall. (this again shows stationary object still has friction if not all things will fall.

U just have to draw the equilibrium diagram n u can see that the stationary object on a level plane will not have friction.
There are only 2 arrows, one is the mass of the object acting on the surface, n the other the opposite n equal reaction from plane to object.

[verykiasumummy]

nebbermind, do u find the info from the guides a little contradicting each other???

[AWSP]

The precise answer is :

a) whether there is any friction or not depends on whether there is any force applied on the object or not and the direction that it is applied. If on the slope, a force is applied such that there is a component of the same magnitude that is opposite and equal to the vector force due to gravitational force, the frictional force will be zero as well.
b) likewise if there is any force applied such that a net horizontal resultant vector force exist on the object on the horizontal surface, there is friction (whether it moves or not).
I dont think all these are spelt out clearly in the question. The setter did not specify the forces applied and he could also not specify because even if he did, in order to comprehend the full implication, the student need to know how to vectorise the forces and newton’s 1st and 3rd law.
This is an extreme case of a setter who is trying to test for "intuition" but does not have sufficient knowledge to set the context properly.
In my opinion, it is an "illegal" question and we should challenge it with MOE.

[Bookwrappers]

verykiasumummy:

kwcllf:

[quote=\"verykiasumummy\"]i'm not proud to say that i have at least 10 sci guides at home... let me look thru all of them and give u all my conclusion since i have the resources available...

No wonder you call yourself \"verykiasumummy\"

sorry ya... it is 23 sci guides.... oh my god.... :yikes: :yikes: :yikes:[/quote]Wow ksmummy, how to get 22 sci guides in the first plc? Wun u forget n buy 2 of the same?

[Bookwrappers]

AWSP:

The precise answer is :

a) whether there is any friction or not depends on whether there is any force applied on the object or not and the direction that it is applied. If on the slope, a force is applied such that there is a component of the same magnitude that is opposite and equal to the vector force due to gravitational force, the frictional force will be zero as well.
b) likewise if there is any force applied such that a net horizontal resultant vector force exist on the object on the horizontal surface, there is friction (whether it moves or not).
I dont think all these are spelt out clearly in the question. The setter did not specify the forces applied and he could also not specify because even if he did, in order to comprehend the full implication, the student need to know how to vectorise the forces and newton's 1st and 3rd law.
This is an extreme case of a setter who is trying to test for \"intuition\" but does not have sufficient knowledge to set the context properly.
In my opinion, it is an \"illegal\" question and we should challenge it with MOE.

The question seems to be so over debated on the answer. Will be eager to see how the answer look like in the next year psle 5yr series. I guess till then that we will all know the answer ba.