=Friction= Friction is a contact force that opposes sliding when one object rubs against another object. Friction does not always oppose the motion of an object. Recall from '''FORCES - NAMES AND DIAGRAMS''' that forces can also be the cause of motion, such as a person walking or a ball rolling. [image:] Friction occurs because no two surfaces are perfectly smooth. As the two surfaces slide past each other small peaks and troughs collide, bonds are broken and heat is generated as a result. This explains why surfaces frequently subjected to friction heat up and often 'wear away'. [image:] The force due to friction depends on the surface types, how fast the objects are moving and the force pushing them together (the weight force for the box above or load force for the diagram on the left). During many energy transformations, energy is released as heat because of friction. For instance when a block slides down a ramp its Gravitational Potential Energy is converted to Kinetic energy. However, some energy is also released as heat and therefore the block might not be travelling quite as fast as predicted at the bottom of the ramp using the conservation of energy.
Credit: Tristan O'Hanlon, Ben Himme