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Name: KH
Status: educator
Age: 20s
Location: N/A
Country: N/A
Date: 1999 

Thanks for answering the following questions.

a) Will a ball roll without friction?
b) Does a ball need friction to roll?
c) If you push a ball, will it always roll?

a) Will a ball roll without friction?

No. Somehow you must provide the torque to start the ball rolling. Normally this comes from friction.

b) Does a ball need friction to roll?

Technically no, but practically yes. Rolling implies that the rate at which the ball is spinning is proportional to the rate at which it is moving. Friction provides the constraint that keeps these equal as the ball changes speed, e.g., when going up or down a hill.

c) If you push a ball, will it always roll?

On a frictionless surface, the ball would not roll at all, but slide -- as bowling balls tend to do in the first part of their trip down the alley.

Tim Mooney

Assuming that by rolling you mean rolling on and against a surface, my guess is that (a) No, (b) Yes, and (c) No, it will slide.

Dr. Ali Khounsary
Advanced Photon Source
Argonne National Laboratory
Argonne, IL 60439

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