Rolling a cylinder down a incline

[MatthewQueen]

if a cylinder rolls down and incline without slipping

then i decrease the coefficient of friction and it does slip a little will it have more, less, or the same kinetic energy as before

I think less, my physics teacher says the same

 

[xxChrisxx]

Welcome.

What is the formula for kinetic energy? Why do you think it will have less?

 

[IPhO' 2008]

If a cylinder doesn't slip its kinetic energy won't decrease.
If a cylinder slip its kinetic energy will decrease.

 

[MatthewQueen]

if you don't know the formula for kinetic energy then you cannot help me

 

[MatthewQueen]

that's what i thought, can you explain why?
my physics teacher won't believe me

 

[xxChrisxx]

I know what the formula is. We try to help you work your way to the answer as opposed to just giving you the solution.

So explain your reasoning as to why you think that the kinetic energy will decrease.

 

[MatthewQueen]

.5mv^2 and .5Iw^2

 

[MatthewQueen]

because its slipping and there is friction

 

[MatthewQueen]

we arent considering air resistance

 

[Bob S]

we arent considering air resistance

Above a certain slope angle, the cylinder will stop rolling and slide. Find the angle.
Bob S

 

[rcgldr]

If the friction is non-zero and there is slippage, then some of the energy is converted into heat by the sliding friction. You mention the two components of kinetic energy, linear and angular. You should work out an example, for a given angle and coefficient of dynamic friction (assume the initial state involves sliding), what is the energy lost due to friction (mgh - total energy of cylinder when it reaches bottom of incline)?

 

[Phrak]

Hmm. MatthewQueen is asking for a formula.

First;
If there is no friction, there is no energy lost to heat.
If there is 100% rolling friction, as in a lossless gear rolling down a rack, there is no energy lost to friction.

Secondly, the kinetic energy is less with any degree of rolling friction--100% or otherwise, as the potential energy is partitioned between the kinetic energy of the center of mass, and the rotational energy.

 

[IPhO' 2008]

When the cylinder slipping , it similar to a box move on the ground. So when the cylinder slip. Some kinetic energy will lost to heat. The kinetic energy that lost to heat is fs
where f is the friction
s is the distance

 

[rcgldr]

The kinetic energy that lost to heat is fs, where f is the friction, s is the distance

For a sliding box this is true, but for the cylinder that friction force is used to increase the angular kinetic energy, so the heat loss would be less than fs.

 

[IPhO' 2008]

I think the increasing angular kinetic energy caused by the decreasing potential energy of the cylinder.
or have I misunderstood?

 

[rcgldr]

I think the increasing angular kinetic energy caused by the decreasing potential energy of the cylinder.

Both linear and angular kinetic energy increase as gravitational potential energy decreases (as the cylinder rolls and slips down the incline). The question is how much energy is lost due to friction as heat for a given coefficient of dynamic friction and slope angle? Then again, if the answer is to simply know that the total energy of the cylinder will less in the case when friction converts some of the potential energy into heat, then knowing the exact amount of the loss isn't needed to answer the original question.