Friction is a force that resists the movement of one object along another object. If they aren’t moving – that is, if the force trying to move them is weaker than the friction -- the friction is static. If they are moving – so the force trying to move them is stronger than the friction – the friction is kinetic.
If one of the objects is a wheel or ball, you may get rolling friction. If the force trying to move it is enough to overcome the static friction, the wheel or ball will slide. However, if it is not enough to overcome the static friction, it will start to roll. There is still friction during rolling, but it is weaker.
Finally, there is fluid friction. If one of the substances is a fluid (liquid or gas) there will still be friction. The viscosity of the fluid determines how much friction there is. So, if you stuff a tube with heavy grease, it will take a lot more force to move it than if it were filled with water.
The cause of friction is electromagnetic attraction between the two objects called molecular adhesion. To slide the objects you have to break those bonds. Friction can be increased if the surfaces are very rough or if one is soft enough that one object digs into the softer one.
No comments:
Post a Comment