Science and Math For Technology
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Friction Friction is a force which tends to interfere with movement between two surfaces. Friction makes all mechanical devices less efficient because more energy is used to accomplish a certain amount of work. Friction provides traction, which is necessary for walking and riding a bicycle [as well as keeping a race car on the track]. Friction is greatest just before movement starts. This is called static friction. Once an object is moving and surfaces are rubbing together, the friction changes and is known as sliding friction. The resistive force of sliding friction is less than that of static friction. The amount of resistance to motion from friction depends upon the kinds of materials and surfaces of the materials rubbing together. Sliding friction is defined by the Greek letter ‘µ’(mu). Wheel axles and spinning shafts can be mounted as sleeve bearings, which produce low sliding friction.   
   
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