Why are spaceships provided with heat shields?

Hint: Spaceships experience large frictional forces while moving through the Earth’s atmosphere because when spaceships enters in atmosphere of each it’s velocity becomes very high. Due to this it experiences very high frictional force on its surface.

Complete answer:
While entering or leaving the Earth’s atmosphere, spaceships go through a large amount of friction or drag due to the atmosphere. Due to the very high speed and acceleration of a spaceship, the magnitude of frictional force is very large. Huge amount of energy is dissipated due to these resistances and the dissipated energy is converted to heat mostly. Without a shield, the spaceship would burn in no time. So, heat shields are used to protect the spaceships. Elements like silica are used in the shield. These absorb most of the heat produced due to friction.
Note: In general whenever we go against friction the temperature of the surface becomes very high and also can catch fire. In the case of spaceships the shields behave as heat sinks which release the heat in the atmosphere after absorbing it.