can static friction do work?

[sv3]

Kinetic friction works over a distance so it does work. I get that. How about static friction? Technically it works over a distance (i think) but b/c this distance is quite small, does it do a material amount of work?

Had a question that asked me how much work friction did as a block was pushed along a surface and friction was present in both forms. The block started from rest. I don't have the answer but was just wondering aloud......any thoughts?

thanks
sv3

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[Isoprop]

It does no work. Work = F*d. Because d = 0, work = 0.

 

[loveoforganic]

I'm thinking this might not be applicable to standard rules since it's an accelerating reference frame, but if you had a box sitting on the roof of a uniformly accelerating car?

 

[sv3]

Interesting - i have no idea how to view that situation about the box on the car???. I thought that the larger the area over which the two surfaces make contact, the larger the possiblity that static friction does work. I'm prolly thinking about it wrong but its something that's been bugging me ever since i studied friction. I mean you have to put in energy to overcome it right? But the fact that the distance is minute or non existent makes me want to learn towards saying no work.......just feels uncomfortable.

 

[Eye Cue]

I'm thinking this might not be applicable to standard rules since it's an accelerating reference frame, but if you had a box sitting on the roof of a uniformly accelerating car?

I believe in that case, you would have to define your system. If your system is just the box, then the 'd' variable would be how far the box moved along the roof of the car, if at all. If you define your system as the car AND box (or simply just car), then the 'd' variable would be how far the car moved.

This is how I would approach it, but don't take my word fully without confirming it with others.

 

[Isoprop]

The car is doing work on the box. The static friction causes a force on the box and causes a change in displacement on the box.

The box does an equal amount of force on the car but does cause a change in displacement of the car. So the box does no work on the car.

The easiest way to check if something does work on another is to see if there is a change in kinetic energy.

The box experiences a change in kinetic energy. Where is it coming from? Obviously, the car. So that means the car is doing work on the box.

The car experiences a change in kinetic energy. Where is it coming from? From the force of the tires. What about the box? No, the box cannot change the kinetic energy of the car no matter how much force it causes. It's because the force on the car is not external. To use an analogy, when you are driving, you cannot make the car go faster by pushing on the steering wheel.

 

[ChemEngSoonMD]

Kinetic friction works over a distance so it does work. I get that. How about static friction? Technically it works over a distance (i think) but b/c this distance is quite small, does it do a material amount of work?

Had a question that asked me how much work friction did as a block was pushed along a surface and friction was present in both forms. The block started from rest. I don't have the answer but was just wondering aloud......any thoughts?

thanks
sv3

If static friction could do work, all we would have to do is put a buncha boxes on a slanted hill and it would solve the worlds energy problems.

 

[b2sun]

If static friction could do work, all we would have to do is put a buncha boxes on a slanted hill and it would solve the worlds energy problems.

Reading this topic, i was actually expecting you to link wikipedia with some douchey comment.

However this was quite clever.

 

[BerkReviewTeach]

To use an analogy, when you are driving, you cannot make the car go faster by pushing on the steering wheel.

But I can make it go faster by pushing on the accelerator!

Seriously though, that's an excellent explanation you gave. Sorry to take away from it with a smart a** comment, but I just couldn't resist.

 

[ChemEngSoonMD]

Reading this topic, i was actually expecting you to link wikipedia with some douchey comment.

However this was quite clever.

Well if the post was "What is Kinetic Friction" instead, you would have probably guessed right.