PSLE 2012 - Science

[creamyhorror]

Fat Mama:

I think the qn the kids discussing is :


Is there friction acting on a stationary box resting on a horizontal surface.

If the surface is stationary, then I would say no, there's no friction acting on the box. If the surface starts to move, then friction starts to act on the box.

It's a tricky question for primary school, I think. These are things that are clarified in secondary physics.

[Fat Mama]

Both box and surface is stationary. So any friction acting on the box?

[ultimateschooler]

The force of friction is a force acting from a surface in the opposing direction of the body’s tendency to slide. It is due to both the normal force pushing from a surface against a body and a condition of the surface called the coefficient of friction. Dependent on whether the body is at rest or moving there is a different coefficient of friction. Static friction is used when the body is at rest and is defined by

Ffriction=Nμs

where Ffriction is the force of Friction, N is the normal force, and μs is the coefficient of static friction. Kinetic friction is used when the body is sliding along the surface and is defined by
Ffriction=Nμk
where μk is the coefficient of kinetic friction

[ultimateschooler]

Static friction > 0.

[Campbell]

Regarding the question concerning mist - actually the answer is very easy.

Ans: The tiny droplets or fog, quickly evaporate, cooling the surrounding air.

[RVHS]

ultimateschooler:

The force of friction is a force acting from a surface in the opposing direction of the body's tendency to slide. It is due to both the normal force pushing from a surface against a body and a condition of the surface called the coefficient of friction. Dependent on whether the body is at rest or moving there is a different coefficient of friction. Static friction is used when the body is at rest and is defined by

Ffriction=Nμs

where Ffriction is the force of Friction, N is the normal force, and μs is the coefficient of static friction. Kinetic friction is used when the body is sliding along the surface and is defined by
Ffriction=Nμk
where μk is the coefficient of kinetic friction

The force of friction is a force acting from a surface in the opposing direction of the body's tendency to slide[/color]
if someone try to push but box still stationary, then there is friction
so for A, no friction as no push or pull force.

[charsen]

Hi

I am back.Overall,the paper was quite ok.The booklet A was quite tricky but it is easy to solve once you know the topic and concept.Booklet B,hmm,a lot of explanation questions.I took a long time for the mist question.I like that kind of question as it is an application question.I wish all the best to all those who are having their higher mother tongue.
For those who have completed their PSLE like me,congratulations! Letd have a goooooooooooooood break for all the hardwork we’ve done

Charsen

[charsen]

RVHS:

ultimateschooler:

The force of friction is a force acting from a surface in the opposing direction of the body's tendency to slide. It is due to both the normal force pushing from a surface against a body and a condition of the surface called the coefficient of friction. Dependent on whether the body is at rest or moving there is a different coefficient of friction. Static friction is used when the body is at rest and is defined by

Ffriction=Nμs

where Ffriction is the force of Friction, N is the normal force, and μs is the coefficient of static friction. Kinetic friction is used when the body is sliding along the surface and is defined by
Ffriction=Nμk
where μk is the coefficient of kinetic friction

The force of friction is a force acting from a surface in the opposing direction of the body's tendency to slide[/color]
if someone try to push but box still stationary, then there is friction
so for A, no friction as no push or pull force.

Hi
There is friction when the object is in contact in the ground.Known as static friction.Not sure of this question,but since there is static friction,there is friction acting on the object.
Charsen

[Ontheballmother]

One more qn - pl help. Something like that - cant recall actual qn.

What is the diff between mammals and birds?
A) bird has wings
B) there are body covering

Tks in advance.

[Haneyi]

Ontheballmother:

One more qn - pl help. Something like that - cant recall actual qn.

What is the diff between mammals and birds?
A) bird has wings
B) there are body covering

Tks in advance.

Hello,
I put body covering as the answer.

Birds -> Feathers
Mammals -> Fur / hair

Hope this helps. ^^