\begin{definition}[Definition:Friction]
'''Friction''' is a force whose tendency is to reduce the velocity of a body relative to its surroundings.
It is caused by interaction of the matter in the body with that of the environment in which it is traveling.
'''Friction''' is (at a fundamental level) an electromagnetic force.
That is, bits of the medium in or on which the body is traveling get in the way (on a molecular level) of bits of the body.
The less friction, the less the reduction in velocity.
If there were no '''friction''', then motion would continue for ever.
{{:Definition:Friction/Coefficient}}
\end{definition}