Friction

You can also walk faster on a smooth surface because there is less friction than on a rough road, which has greater friction. When you walk, the sole of your shoes and the ground rub against each other, thus creating friction.

The amount of friction depends upon the smoothness of the two surfaces touching each other. If the soles of your shoes have deep canals and the ground is not slippery, you can walk straight without falling because of the resistance caused by high friction. However, if the soles of your shoes are already smooth or worn out, then you may slide down the ground because less friction resists the movement. Basketball players usually wear rubber shoes with deep canals on the soles to avoid sliding down while running in the court. They need to increase friction to prevent accident.

Friction in the Air
Friction also exists in the air. Get two pieces of paper and then crumple one of them. Hold the pieces of paper, with one on each hand. Drop both pieces from the same height at the same time. Observe which piece of paper reaches the floor first. You will notice that the crumpled paper falls down faster. This is because it has less exposed surface. It produces less friction with air as it falls down. On the other hand, because the exposed surface of the paper that was not crumpled is greater, there is greater friction with the air. Thus, this paper falls down more slowly, proving that there is also friction in air. This type of friction depends on the surface area of the objects that is exposed in the air.

Friction in Water
There is also friction in water. This can be observed when watering plants in a garden using a hose. Water moves through the hose easily because it has low viscosity, or the property of a liquid that causes it to resist flow. Thus, water produces low friction with the lining of the hose. Other fluids like grease, which has high viscosity, would have a harder time moving through the hose because they produce higher friction. Friction causes water resistance, which slows down swimmers and boats traveling through the water.