Force & Friction

Simply put a force is a push or a pull. A force is an action the causes some kind of reaction from another object. Force is also a vector; it has both a direction and magnitude. Forces also require and agent, a cause of the force. There are two types of forces. A contact force, a force that depends on the agent touching the object or not and a long-range force, a force tat acts on an object without any physical contact, such as gravity.
push
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http://physics.tutorvista.com/forces.html
Friction is an agent of force. A frictional force is a force exerted by a surface and is always tangent to the surface. There are two kinds of friction, kinetic friction and static friction. Kinetic friction happens when an object slides across a surface and it opposes the motion, meaning that the friction force vector will point in the opposite direction as the velocity vector. Static friction is the force that keeps objects stationary on a surface, it prevents motion. The static friction vector will point in the direction that is necessary to prevent motion.
friction
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http://www.school-for-champions.com/science/friction.htm#.VTXj9zvF8i4