Question

POTENTIAL AND KINETIC ENERGY

OBJECTIVES: To determine the potential and kinetic energy of a freely falling body To determine the loss in kinetic energy of an inelastic collision To calculate the percentage error of the experimental error of the velocity of a freely falling body using the conservation of mechanical energy of a body

MATERIALS: Tennis balls Digital Timer Meter stick

THEORY: Conservation of Mechanical Energy A body raised to a certain height possesses potential energy due to its position. Since work was done to lift the body to a certain height, the body gains potential energy. When the body is released from its position, the potential energy is transformed into kinetic energy on its way down. Upon reaching the ground, the potential energy is converted into kinetic energy. Ideally, if there is no loss in kinetic energy, the body should bounce back to its original height. This only happens for a perfectly elastic collision Inelastic Collision In most situations however, once the body reaches the ground, some of its kinetic energy is lost (e.g., the body undergoes slight deformation upon collision with the ground). The body will then reach a lower maximum height than the original height from which it was dropped. Eventually, the body will lose all its kinetic energy and will rest on the ground once all of its kinetic energy is lost. In this case, the collision is inelastic; that is, kinetic energy is not conserved.

Procedural Instructions: Decide as a group the original height from which the ball will be dropped. Record this in your data table. After the ball bounces up twice, record also the maximum height reached by the ball for each bounce. Assign one member to note these two maximum heights. Assign three members to record the time for the ball to reach the ground from its original height, first maximum height, and second maximum height. Note that three members would be needed to measure these different times. Record these in your data table. Complete your data table to find for the velocity of the ball each time it reaches the ground. You are responsible for the equation that should be used. Using the times and the corresponding heights you have recorded, discuss as a group the appropriate formula to be used and apply them. Record your results in your data table. Using your equations for kinetic and potential energies, again, discuss as a group the appropriate formula for determining the theoretical value of each velocity you have computed and apply it. Record your results in your data table. Compute for the percentage error for each velocity.

QUESTIONS AND PROBLEMS: What is the percentage error on each of the velocities in your experiment? Discuss with your members what could have caused this error. How is the loss in the kinetic energy manifested by the ball each time it reaches the ground? In your experiment, calculate the kinetic and potential energies when the ball was on its midway down the first, the second, and the third time. What can you conclude about the total mechanical energy of the ball as its falls down the ground?

DATA TABLE

	Initial Max Height	Second Max Height	Third Max Height
Potential Energy     (from Max Height)
Kinetic Energy    (upon reaching ground)
Time
Experimental Velocity
Theoretical Velocity
Percent Error

Answer 1