Frictional forces are formed when two objects move against each other. These are forces that move in opposite directions, making it harder for an object to move.
There are greater frictional forces on rigid surfaces than on smoother surfaces.
Sometimes, friction is helpful:
However, sometimes friction is not helpful:
Holding objects – To hold onto any object, friction is required. If there is no friction, objects will slip out of your hands.
Using an eraser – When you rub an eraser on paper, it overcomes the frictional force that the lead particles (from the pencil) have with the paper.
Polishing rough surfaces – You can use sandpaper to polish rough or sharp edges to make them smoother. There are more irregularities on rough surfaces than on smooth surfaces. So, the rough and rigid surface of sandpaper helps to increase friction and break the irregularities on the rough surfaces, so they become smoother.
Tug of war – In this game, there are two teams pulling on a long rope. The friction is between the players’ hands and the rope, which helps the players to maintain grip on the rope.
Forest fires – Trees can rub against each other due to high wind velocities. This builds up friction and heat, which can lead to forest fires.
Climbing trees – There are many animals that have sharp claws, hairy feet or both. These can be used to climb trees. For example, there is great friction between the animals’ claws and the rough surface of the tree.