Friction is the opposing force that is set up between the surfaces of contact when one body slides or rolls or tends to do so on the surface of another body.
For example, if a book on a table slides from left to right along the surface of a table, a frictional force directed from the right to left acts on the book at the surface of contact i.e. In between the two surfaces and parallel to the surface.
Frictional forces may also exist between surfaces when there is no relative motion. Frictional forces arise due to molecular interactions.
- If lubricants are used, then the force of friction generally reduces.
- In some cases, friction acts as a supporting force, and in some cases, it acts as an opposing force.
Frictional forces are essential in many walks of life. For example, the walking process can only take place because there is friction between the shoes and the ground. In the process of walking, in order to step forward, you must press your foot backward on the ground. A friction force tends to oppose this movement of the foot, the ground pushes you forward which allows you to walk. When there is no friction, as on ice, or polished granite, or oily surfaces, the walking is difficult.
When a block slides over a surface the force of friction work as an opposing force in the opposite direction of the motion.
(c) Both Supporting and Opposing:
When a cyclist pedals the friction force on the rear wheel acts as a supporting force and on front-wheel as an opposing force.
When a cyclist does not pedal the friction force on the rear wheel & front wheel act as an opposing force.
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What is Static Friction
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