Question

Why do sportsmen use shoes with spikes?

Answer 1

Hint: Try to think in terms of grip-aided mobility at running speeds. In other words, spikes are sharp structures that have a mostly pointy end. Does the area of contact between the shoe and the ground reduce with spikes? Think of how this would affect the amount of pressure that would be exerted on the ground and consequently how friction would come into play here. Account for how this would contribute to the physical safety of the sportsman as well.

Formula used:
Pressure $P_{ground} = \dfrac{F_{frictional}}{A}$, where A is the area of contact and $F_{frictional}$ is the frictional force produced.

Complete step by step answer:
In general, shoes have treads and grooves underneath. Sportsmen, especially those whose sport requires them to be mobile and quick at their feet, such as runners, field players, etc., usually wear shoes that have spikes at the bottom in addition to the treads underneath.
The main reason to do this is to increase the friction between the shoes and the ground, ensuring a better overall grip to the sportsman.
While running very fast, it becomes easy to lose contact with the ground and slip, which may cause injuries. Thus, a mechanism is required through which better grip is achieved. This is done by including spikes at the bottom of the shoe, wherein the spikes are able to hold on to the ground, just enough to prevent slipping while ensuring that at the same time, speed is not compromised. Spikes are basically sharp structures made up of a rough material. Since the area of contact between the spikes and the ground is much lesser when compared to the whole base of the shoe and the ground, there is more pressure exerted on the ground which increases the frictional force between the shoe and the ground and ensures that a better grip is achieved.
$P_{ground} = \dfrac{F_{frictional}}{A}$

Note:
The same principal of friction comes into play in case of drilling a screw into a wall. The screw usually has treads or grooves on its tail. This is to ensure that the screw stays in the wall due to friction between the grooves of the screw and the wall, without which screw would just slip off. Nails can also be used but one must ensure that the surface of the nail body is rough.