Double Ball Bounce

I. Introduction

• For my Physics PBL project, I have to investigate and answer the driving question, "Why does a ball bounce much higher than the height it was dropped when it is simultaneously dropped on top of a larger, more massive, ball?". This phenomenon occurs because of physics principles such as energy, momentum, and elastic collision.

II. Materials

III. Procedure

1. Obtain the following materials: basketball, tennis ball, and Astro Blaster toy.

2. Find a spacious area that isn't crowded or filled with breakable items. Like an empty hallway.

3. Drop the tennis ball and basketball individually from a 1 meter height.

4. Record the ball's each individual height bounced

5. Then drop the two balls at the same time with the tennis ball on top of the basketball.

6. Record measurements of how high the tennis ball bounced

7. Drop the Astro Blaster toy and compare the height results from the second experiment

IV. Scientific Principles

When a basketball is dropped from a certain height, it consists of a certain amount of potential energy. The potential energy transfers to kinetic energy when the ball hits the ground. When the energy converts, it gives off some of its energy to the ground transforming into heat energy. The same is applied to the tennis ball. The tennis ball and basketball are dropped from about 1 meter. As they fall, they build up speed and when the basketball hits the floor, it has an elastic collision with the tennis ball. Before the drop and collision, the basketball has more momentum because of its larger mass; however, after the collision it transfers most of its momentum to the smaller ball. That is why the tennis ball bounces very high and how come the basketball bounces softly from the floor.

V. Investigation Questions

1. What is "momentum" and how does the momentum of a ball like a tennis ball or basketball change as it free falls from a height of approximately 1 m? How does the momentum of the ball change it bounces off a hard floor?

A: Momentum is the vector quantity of movement an object has that is calculated by multiplying mass by velocity. The momentum of the basketball has more momentum than the tennis ball before hitting the floor. But when the momentum of the basketball hit the floor it transfers most of its moment to the tennis ball.

2. When the basketball hit the floor, a collision occurred between it and the ground. Was the collision elastic or inelastic? What determines if a collision is elastic or inelastic?

A: The collision when the basketball hit the floor was an elastic collision. The determining factor in what makes a collision elastic or inelastic is the amount of kinetic energy of the objects before and after the collision. If the kinetic energy is not conserved, then the collision is inelastic. However, in elastic collisions, there is no loss of kinetic energy.

3. What happens to the momentum of two objects that collide with each other? What are the theories and equations you would need to determine any change in the momentum of either object?

A: The momentum of the two balls that collide with each other is that the tennis ball's momentum increases due to the basketball's momentum being transferred to the tennis ball while the basketball barely rises off the ground. This process can be seen through the conservation of momentum equation: m₁V_1i+ m₂V_2i = m₁V_1f + m₂V_2f.

4. Assuming the tennis ball and basketball had a very small gap between them when the basketball hit the floor, in which directions were the momentums of the tennis ball and basketball just after the basketball hit the floor, but before it collided with the tennis ball?

A: The directions of the momentums of the tennis ball and basketball just after the basketball fit the floor but before colliding with the tennis ball is that the basketball's momentum goes down towards the tennis ball because it has more mass; while the tennis ball's momentum direction is also down but slightly less than the basketball's momentum due to its light weight.

VI. Safety Procedures

I. To avoid being hit in the eye, do not look directly over the balls as they bounce. Or wear safety goggles.

II. Do not drop the balls from an excessive height over 1 meter.

VII. PBL Action Video