Register to reply

2 balls, one rolling, one sliding down the same ramp. Which is faster at the bottom?

by Sockpirate
Tags: balls, faster, ramp, rolling, sliding
Share this thread:
Sockpirate
#1
Oct29-09, 07:52 AM
P: 2
This isn't homework, but I thought that it's probably better in here, as it's a fairly quick question.
OK, so I have 2 identical balls (exact same mass and radius). They rest on the same position on 2 identical slopes (same gradient) and begin to move down the ramps. The only difference is that one rolls down and one slides down (i.e. doesn't roll). Which one reaches the bottom with the greater speed? Assume that the effect of friction is negligible.

OK, so obviously GPE is converted into kinetic energy. This should be the same for both balls, since they start at the same height.
However, would I be right in saying that the rolling ball will move slower (if friction is negligible), as some KE will be rotational and not translational KE?

If friction were not negligible (i.e. it actually had an effect) which one would be faster now? Intuition tells me the rolling ball will, but I can't think why.

Anyway, thanks very much for the help! As I said, it's not homework, just something I'm interested in, but thought it'd probably fit better in this forum ^^
Phys.Org News Partner Science news on Phys.org
New model helps explain how provisions promote or reduce wildlife disease
Stress can make hard-working mongooses less likely to help in the future
Grammatical habits in written English reveal linguistic features of non-native speakers' languages
Doc Al
#2
Oct29-09, 08:13 AM
Mentor
Doc Al's Avatar
P: 41,300
Quote Quote by Sockpirate View Post
Assume that the effect of friction is negligible.
But friction cannot be neglected in the case of rolling without slipping. Without friction, the ball wouldn't roll.

OK, so obviously GPE is converted into kinetic energy. This should be the same for both balls, since they start at the same height.
However, would I be right in saying that the rolling ball will move slower (if friction is negligible), as some KE will be rotational and not translational KE?
If you compare something that slides without friction down the ramp to something that rolls down the ramp, you are absolutely correct.

If friction were not negligible (i.e. it actually had an effect) which one would be faster now? Intuition tells me the rolling ball will, but I can't think why.
I haven't done the calculation, but I imagine it would depend on the coefficient of friction. (Note that for the case of rolling without slipping, the speed down the ramp does not depend on the coefficient of friction, so long as it's enough to prevent slipping.)


Register to reply

Related Discussions
Distance travelled by the case down a ramp w/a spring at the bottom Introductory Physics Homework 5
Sphere Rolling vs. Sliding Down a Ramp Introductory Physics Homework 4
Normal Force of a skateboarder at the bottom of a circular ramp Introductory Physics Homework 2
Sliding/rolling billiard balls General Physics 8