Phys Lab

Mechanical Energy of a Bouncing Ball Post-lab

In this lab, we gained experience observing energy conservation, energy dissipation, and how energy is transferred and transformed. Energy is conserved when only conservative forces are at work and when the system is closed. Conversely, energy is dissipated when there are dissipative forces such as friction or when the system is not closed and is allowed to interact with the surrounding environment. In the first part of the lab, we measured the motion of a basketball bouncing on a stool with a certain height. The height of the stool is where we defined gravity to be zero. Therefore, change in height of the basketball is the total distance between the motion sensor and the stool subtract the position of the ball measured by the sensor. The total mechanical energy of the basketball is its gravitational energy plus its kinetic energy. Theoretically the total mechanical energy graph should be a decreasing linear relation with regular dips. This is because that each time after the basketball hit the stool, it bounced up lower than the previous time. This means the kinetic energy and the potential energy are mostly transformed and should add up to the same total. The graph should slightly decrease because each time the ball hits the stool, it’s interacting with the outside environment and dissipative forces such as friction are involved, causing a dissipation of energy. There are dips in the graph because the instant ball hits the stool, it has no gravitational potential energy and no kinetic energy (since it’s not moving); the sum then, is therefore 0. However, this does not mean the ball has no energy whatsoever at that moment. The ball can act somewhat like a spring and when it comes into contact with the stool, it compresses inward towards its center of mass, and therefore the mechanical energy is transformed into elastic potential energy. The elastic potential energy allows the ball to bounce back up even though its...