PSLE 2012 - Science

[verykiasumummy]

i think for the frog and tadpole question, students should answer :


the tadpoles and frogs live in different habitat, therefore if one of the habitats is destroyed, the population of frogs or tadpoles will still continue to survive since they are not dependent on the same habitat.
the tadpoles and frogs feed on different source of food, therefore if one of their food source is greatly reduced, the population of frogs or tadpoles will still continue to survive since they do not depend on the same kind of food for survival.

[verykiasumummy]

as for the friction question, i still think in the point of view from a P6 student, they should choose all of the set ups as all they learn about friction is friction is a type of contact force. when 2 surfaces are in contact, they have friction.


i’m not sure if to disagree that stationary objects do not have frictional force acting on them. because gravitational force acts on the object, which causes it unable to overcome the frictional force (horizontally) between the 2 surfaces, therefore it remains stationary. if the object is 10N, means gravitational force acting on it is 10N, so in order to move it horizontally, it will also need minimum 10N to overcome its frictional force which is also 10N…

am i correct in interpreting this from the view of P6 student??

[Nebbermind]

Sun_2010:

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

You are RIGHT!!

There is a normal force acting on the object and nothing else. Therefore there's no frictional force.

[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…

[Nebbermind]

Now I'm not even sure (c) has frictional force. What if it is a fictionless surface? :scratchhead:

[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.