| − | A [[force]] resulting from the contact of two surfaces. This force opposes motion.<ref>Wile, Dr. Jay L. ''Exploring Creation With Physical Science''. Apologia Educational Ministries, Inc. 1999, 2000</ref> | + | A [[force]] resulting from the contact of two surfaces. This force opposes motion.<ref>Wile, Dr. Jay L. ''Exploring Creation With Physical Science''. Apologia Educational Ministries, Inc. 1999, 2000</ref>. For solid bodies, one can distinguish two types of friction: |
| | + | For solid surfaces, both types of friction depend (to a good approximation) only on the [[normal force]]. In particular, the dynamic friction does not depend on the velocity.<ref>Marcelo Alonso and Edward J. Finn, ''Fundamental University Physics'', Addison-Wesley.</ref> |