FRICTION
When two objects which are touching try to move past each other, they rub against each other. This produces a force called friction which tries to stop the movement. If the surfaces of the objects are rough, like sandpaper, then friction is greater. If they are smooth and slippery, especially if lubricated with oil or grease, then friction is less. Friction is “the enemy of machines”: it opposes movement, causes wear and tear, and changes useful energy into waste heat. But friction can also be helpful. A vehicle slows down suddenly because of friction provided by its brakes. A bulldozer’s tracks dig into the earth with so much friction that they cannot slip. So the bulldozer can push huge mounds of soil.
A skier slides easily over snow and ice because the skis press down and rub hard on them. The friction makes them heat and melt into water, which is very slippery with low friction. After the skis have past, the snow and ice freeze again.
Picture Credit : Google
