Mechanical energy of a ball is the sum of its gravitational potential energy and kinetic energy. Symbolically, this relationship can be expressed as: ME=PEg+KE. When a ball is raised off the ground via a force, an opposite, equal force exists (according to Newton’s 3rd Law) and is called the restoring force. The restoring force times the height is the potential energy of an object, which has the potential to travel back towards the Earth due to gravity when raised a certain height. Therefore, the higher the ball is displaced from the ground, the more potential energy it has. This potential energy is then transferred to kinetic energy when the ball travels towards the ground. Kinetic energy occurs when an object exerts energy in motion.
As the ball reaches its maximum kinetic energy, it encounters the ground, which transfers energy thermally via friction. When the ball makes contact with the ground, some of its energy is lost to the physical ground. Because balls are designed to contain a fraction of their original energy, so they can bounce, the transferred thermal energy reduces the ball’s motion, but the ball still has kinetic energy remaining to bounce back up to a fraction of its drop height. Thermal energy causes atoms and molecules to move faster, thus causing a rise in temperature.
Temperature is the measure of heat transferred to an object through equilibrium. So, when the ball makes contact with the ground, we can expect both the ground and ball to increase in temperature. This is because the transfer of heat works to create thermal equilibrium.