You might have noticed that when used for a long time, slippers with rubber soles become slippery. Explain the reason.
Hint: In order to answer this question, you must be aware about the concept of friction. It is a force between two surfaces that are sliding, or trying to slide, across each other. Friction always works in the direction opposite to the direction in which the object is moving, or trying to move.
Complete answer: After wearing slippers for a long time, the sole becomes smooth because of the continuous rubbing of the sole of the slippers with the floor. The smooth surface of the sole reduces the necessary force of friction between the slippers and the floor and hence the slippers become slippery. This does not allow us to walk properly on the ground. One can even fall down because of the slippery sole.
Note: The main cause of friction is the roughness or smoothness of an object. When two rough surfaces come in contact with each other, they generate frictional force or an opposing force, which can sometimes be converted into heat. When the roughness of the road increases, the degree of friction increases because it is more difficult to walk on a road with many pebbles and easier to walk on a levelled road.