Law of Energy Conservation
The Law of Conservation of Energy states that energy cannot be created or destroyed, just transformed into a different type of energy that is no longer useful. Using Energy Transformation Diagrams, we are able to show how the energy is transformed during the tennis shot, and where it goes.
Racquet:
At first, the racquet is lifted up using chemical energy from our muscles. This chemical energy becomes kinetic energy, since the racquet is moving, and then gravitational potential energy at its maximum height. Then, when we swing it back down, this gravitational potential energy turns back into kinetic energy. This kinetic energy carries the racquet towards the ball. When it hits the ball, the kinetic energy becomes three different types of energy. The first type is sound energy. This is the popping sound we hear when the ball is hit. Some of the energy also goes to thermal, since the ball is rubbing against the strings of the racquet, which creates heat. The third type is elastic. When the ball hits the strings, the strings act like a spring, stretching back and gaining elastic energy. Then, when this energy is released, it turns back into kinetic, and eventually, when the racquet reaches the top of the swing, all the energy remaining is turned back into gravitational potential energy.
Racquet:
At first, the racquet is lifted up using chemical energy from our muscles. This chemical energy becomes kinetic energy, since the racquet is moving, and then gravitational potential energy at its maximum height. Then, when we swing it back down, this gravitational potential energy turns back into kinetic energy. This kinetic energy carries the racquet towards the ball. When it hits the ball, the kinetic energy becomes three different types of energy. The first type is sound energy. This is the popping sound we hear when the ball is hit. Some of the energy also goes to thermal, since the ball is rubbing against the strings of the racquet, which creates heat. The third type is elastic. When the ball hits the strings, the strings act like a spring, stretching back and gaining elastic energy. Then, when this energy is released, it turns back into kinetic, and eventually, when the racquet reaches the top of the swing, all the energy remaining is turned back into gravitational potential energy.
Ball:
At first, chemical energy from our muscles is used to lift the ball. This lifting creates motion, and the chemical energy is transformed into kinetic energy. Next, at the top of the ball's ascent, all the energy becomes gravitational potential energy. Then the ball is dropped, and that potential energy becomes kinetic energy until the racquet hits it. When the racquet comes into contact with the ball, three types of energy occur. The first is sound, which attributes to the popping sound as well, the second is thermal from the ball rubbing against the strings, and the third is elastic. When the ball hits the racquet, it gets squished, and it gains elastic energy, since it is compressed. Naturally, since there is pressure inside the ball, it will want to regain its original form, and when this happens, the elastic energy is turned back into kinetic energy. This energy is used to move the ball up, and at its max height it will have turned into gravitational potential energy once more. Then, as it falls, that energy becomes, once again, kinetic energy. When it hits the ground, some of the remaining energy goes towards more sound energy, some goes towards more thermal energy from rubbing against the ground, and the rest becomes elastic energy once again, since the ball compresses again. The ball then bounces back up, and this energy then becomes kinetic and then potential again once it reaches the top. This cycle from gravitational potential to kinetic to elastic, thermal and sound, back to kinetic and then back to gravitational potential again will continue until all the energy is turned into thermal and sound, at which point the ball will stop bouncing/moving.
Energy Conservation Calculations
We can calculate the amount of kinetic energy the ball has at any point during its flight as well using this law. Since there will never be energy lost, we know that the total energy at any two points will be the same. The only thing that changes is the form the energy is in. Lets say, for example, that a player was trying to hit a volley off of this shot, and he wanted to know how fast the ball would be moving at the point of his volley. The height he wants to hit the volley at is exactly 1.50m. To find the speed of the ball at that point, we must use our energy conservation equation to find how much energy is kinetic at that point, and how much is potential, and we must compare them to the total energy at another point such as when it bounces. Once we find the kinetic energy, we can solve for the velocity:
Therefore when the player hits his volley, the ball will be moving towards him at approximately 17m/s.