Question

can static friction do non zero work?

Answer 1

This issue has already been tackled quite at length here:
http://openstudy.com/study#/updates/4f93f2fde4b000ae9eca5280

Answer 2

i guess it cant - after motion comes into action we have sliding friction

Answer 3

@ goutham1995 i too think the same way
static friction acts until there is no motion,no motion means no displacement,so work done by this force is always zero
just wanted to check if my intuition was correct

Answer 4

@vincent-lyon.fr -what do you think?

Answer 5

Your intuition is correct.

Now, let's go to step two: broaden the situation by realising that what is probably implicit in your model is that the body relies on a fixed base. What if the base is moving?

Answer 6

Another doubt that I have.
What about rolling spheres.
Static friction acts on them to make it into pure rolling.
There, Kinetic Energy Changes. So by work energy theorum doesnt friction perform work?

Answer 7

now w'll have to look from the frame of reference of the base and that would be a non inertial frame.but still the fact work done by static friction is always zero should still hold,because once a block kept on a base starts moving static friction ceases to act.we then have kinetic friction

Answer 8

^_^! Let's say rolling spheres or wheels are Step 3 !! We'll tackle those later.

Answer 9

"now w'll have to look from the frame of reference of the base and that would be a non inertial frame."

Well done, it all depends on the frame of ref. you choose. Now the fact that it is or is not inertial is irrelevant.

Answer 10

even if we have a non inertial frame, static friction's work is zero because we must always take it with respect to the surface it is in contact with.

Answer 11

"we must always take it with respect to the surface it is in contact with"

Not necessarily, but in that case, the answer to the initial question is pretty clear.

Answer 12

Imagine a box kept on a car.
Static friction is enough to stop the box.
But wrt the ground both car and box are moving.
Therefore wrt ground, The only force acting on the box, static friction, must have performed some work.

Answer 13

The key word is "frame of ref." Because work done by a force is frame-dependent.
You cannot answer this question unless you state clearly what frame of ref. you are choosing.
Then the answer might not be the same in the different situations.

Answer 14

rolling motion includes translation besides rotation.now since it includes translation,there is no point in talking about STATIC friction

Answer 15

"Therefore wrt ground, The only force acting on the box, static friction, must have performed some work."

Definitely, well done!

Answer 16

Why is there no point in talking about static friction?

Answer 17

I'll be back in apprx one hour and help you out with rolling bodies if necessary.

Answer 18

Thankss.

Answer 19

At point P we have static friction acting. That changes the Kinetic energy of the system to a value to produce pure rolling.