## Exploration 7.2: Choice of Zero for Potential Energy

For the bar graph on the left: yref = 0 m

For the bar graph on the right: yref = where -15 m < yref < 15 m.

The animation depicts a ball being dropped from y = 15 m onto the ground 15 meters below at y = 0 m (position is given in meters and time is given in seconds). For this animation we will assume that the ball undergoes a very hard collision with the ground, which also conserves energy. Also shown are two pairs of bar graphs representing the different types of energy associated with the ball: the kinetic energy (orange) and the gravitational potential energy (blue). The bar graphs on the left show the kinetic energy and the potential energy as measured from yref = 0 m. The bar graphs on the right show the kinetic energy and the potential energy with a varying zero potential energy point. You can vary the zero point from -15 m < yref < 15 m by changing the value in the text box and clicking the "set value and play" button. Restart.

Change the zero point for the potential energy from zero to a variety of positive values and a variety of negative values. Answer the following questions about the animation.

1. For zero points that are less than zero, does the gravitational potential energy shift up or down?
2. Is all of this energy accessible to the ball? In other words, can it all be converted to kinetic energy?
3. For zero points that are greater than zero, does the gravitational potential energy shift up or down?
4. For yref = -15 m, how much potential energy does the ball start out with? How much does it have when it hits the ground? What is the change in potential energy?
5. For yref = 15 m, how much potential energy does the ball start out with? How much does it have when it hits the ground? What is the change in potential energy?