Difference between ball and roller?

What exactly is the difference between ball and roller? I've been studying this topic in my mechanical engineering textbook. Would appreciate your responses.

Is it about bearings?

this is quite simple a ball is a sphere while a roller is a cylinder. both can roll: a ball makes point contact while a roller maks line contact ideally. Speaking of bearings, you can easily visualize and differentiate a ball bearing with a roller bearing by seeing the rolling object in it. generally roller bearings are used in heavy loading conditions to reduce the stresses developed in the bearing.

type of contact explains the difference..ball has a point contact whereas roller has a line contact..A ball is a sphere whereas a roller is usually a cylinder or a frustum(a tapered roller)..!!

maybe this question is about the types of bearings.

it has already been discussed about the type of contacts, balls and rollers , make with flat surfaces.

another point is that balls can easily change their direction of rolling. but a roller on the other hand which is cylindrical (and makes line contact) cannot do so that easily.