# Does friction always result in energy loss?

1. Oct 16, 2015

Hi,

If I have a ball at the top of a ramp, it will have rotational and translational kinetic energy as it begins moving. If the ramp was frictionless, just to confirm, would it be possible for the ball to rotate or would it just slide with the point of contact on the ramp fixed?

Also, if there is friction and the ball is allowed to rotate, will the ball lose energy while it goes from the top of the ramp to the bottom? To my understanding, friction is a nonconservative force and will result in energy dissipated from the system (i.e. the ball). But in this case, if friction is necessary for the ball to rotate, would I have to account for a loss of energy term when trying to figure out the ball's position, speed, and acceleration as it moves on the ramp? In this case, is the energy loss through friction negligible? Would it ever not be negligible?

2. Oct 16, 2015

### BvU

(1) Yes: slide. There is no force to make it rotate.
(2) not necessarily: if it doesn't slide at all the friction force does no work.
(3) mechanical energy is not lost if the friction force only makes the ball rotate (see (2) )
(4) can be safely ignored for e.g. a returning bowling ball that rolls up the ramp for the next shot.
(5) e.g. if there's a lot of sand on a ramp

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3. Oct 16, 2015

### Isaac0427

BvU is correct about the ramp, although there is another form of friction- air resistance. Again, it is very negligible, however you would account for it if you want EXTREMELY precise measurements.

4. Oct 17, 2015

### BvU

Yeah, for a styrofoam ball in heavy fog this doesn't fly at all. So let's assume vacuum