Q:

What are some examples of rolling friction?

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Quick Answer

Examples of rolling friction are a roller skate slowing down on pavement or the wooden surface of a roller-skate rink and a basketball rolling across the surface of the court. When one surface rolls across another, small indentations on both surfaces interfere with each other, reducing speed.

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Full Answer

Friction is a requirement for the beginning, ending and alteration of the movement of a wheel or other rolling object. When a car spins its tires against the road, friction is necessary to stop the slippage and allow the tires to get purchase on the ground and begin their rolling motion. As the tires move, though, the interaction between the indentations on the tire and the indentations on the ground builds a torque that slows the angular velocity of the tire.

As the rolling motion takes place, the shape of both objects change as well. For example, the wheel flattens slightly, while the surface develops a trench that holds the entire flattened edge of the wheel. The force of the friction spreads throughout the whole area at which the surfaces come into contact with one another. The front of the wheel also shrinks a bit in response to making a type of plowing motion along the surface.

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    How do ball bearings reduce friction?

    A:

    Ball bearings reduce friction by using smooth balls lubricated with oil or grease that freely roll between a smooth inner and outer surface. The main concept of the ball bearing is that objects that roll past each other produce less friction than if the objects were sliding against each other.

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  • Q:

    What causes friction?

    A:

    The primary causes of friction are surface roughness, the plowing effect and molecular adhesion. Surface roughness is when serious abrasion occurs due to the roughness of the materials in contact. The plowing effect involves deformations of the objects that cause resistance to movement when the materials are relatively soft.

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    Why is static friction greater than kinetic friction?

    A:

    Static friction is greater than kinetic friction because of irregularities between the static object and the surface upon which it rests. The irregularities mesh together making it more difficult to start movement than to keep the object in motion.

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