My PBL Project

Introduction:

The purpose of our project is to show that energy can't be created nor destroyed, but It can be transferred from one object to another. It also shows that during a collision energy is usually transferred from one object to another.

Driving Question:

Why does a smaller ball bounce much higher than the height from which it was dropped when it is simultaneously dropped on top of a larger more massive, ball?

Materials:

Basketball

Tennis Ball

Camera

Balance

Astro- Blaster

Opitonal Materials:

Astro Blaster toy

PASCO Dynamics cart (2) and track

PASCO Cart Masses, several

PASCO Capstone software

Procedures:

• Hold the basketball about a meter above the floor.

• Drop the basketball and notice how high it bounces.

• It will certainly bounce up to a height lower than the height from which we dropped it.

• Drop the tennis ball, and notice that it too bounces up to a height lower than that from which it was dropped.

• Now hold the tennis ball directly above the basketball so that the balls are touching.

• Then drop both balls at the same time.

• Notice that the tennis ball goes shooting off above your head at a high speed; at a height twice as much as when it was dropped.

Safety:

• The top ball on the Astro Blaster and the tennis ball have the potential to bounce with very high velocity and an unpredictable direction. To avoid being hit in the eye(s), do not look directly over any of the balls as they bounce.

• Do not drop the Astro Blaster or other balls from an excessive height. A height of approximately 1 m is sufficient for all demonstrations.

• When using the carts and track in a collision demonstration, be careful not to have your hand or any other items in the path of the cart.

Essential Understanding/Scientific Principle :

When a basketball is dropped from the a height of 1 meter, it consists of a certain amount of potential energy given by gravity. The potential energy transfers to kinetic energy when the ball hits the floor or surface on the ground. When the energy converts, it gives off some of its energy to the ground causing it to heat up, thus creating heat energy. The energy that is left is used to make the ball bounce back up at least to the waist height. The same is caused for a tennis or racket ball. A tennis ball and a basketball are dropped from about chest height. As they fall, they build up speed. When the basketball hits the floor, it bounces and collides with the tennis ball. Just before the balls hit one another they are both moving at the same speed, but the basketball has a larger mass and therefore more momentum. It turns out that the basketball transfers most of its momentum to the tennis ball. This process can be analyzed through the conservation of momentum equation. The result being that the tennis ball bounces very high, and the basketball barely rises off the ground.

Action Video:

Real Life Connections:

The game of pool provides an example of a collision in which one object, the cue ball is moving, while other balls are stationary. Due to the hardness of pool balls, and their tendency not to stick to one another, this is also an example of an almost perfect elastic collision, which shows kinetic energy is conserved. t should be noted that this illustration treats pool-ball collisions as though they were 100% elastic, though in fact, a portion of kinetic energy in these collisions is transformed into heat and sound. Also, for a cue ball to transfer all of its velocity to the object ball, it must hit it straight-on. If the balls hit off-center, not only will the object ball move after impact, but the cue ball will continue to moves roughly at 90° to a line drawn through the centers of the two balls at the moment of impact. When a cue ball hits an object ball in pool, it is safe to assume that a powerful impact is desired. The same is true of a bat hitting a baseball. But what about situations in which a powerful impact is not desired as for instance when cars are crashing? There is, in fact, a relationship between impulse, momentum change, transfer of kinetic energy, and the impacts desirable or undesirable experienced as a result. Another real life connection would be ,In a highly elastic car crash, two automobiles would bounce or rebound off one another. This would mean a dramatic change in direction a reversal, in fact hence, a sudden change in velocity and therefore momentum. In other words, the figure for m δv would be high, and so would that for impulse, Fδt.

Investigation Question:

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 when 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. When the momentum of the basketball hit the floor it transfers most of its moment to the tennis ball.

2. When a tennis ball and a basketball are dropped, one at a time, on a hard floor they bounce, but the tennis ball or basketball never bounce higher than the point from which it was dropped. Why is this, and what would you need to add to the tennis ball or basketball to have it bounce higher than it was dropped?

3. Place the tennis ball on top of (directly above) the basketball, and then drop the two balls together from approximately 1 m above a hard floor. What happens to the tennis ball and the basketball when they hit the floor? Describe their motion.

4. After the bounce, how were the momentum of the tennis ball and the momentum of the basketball different compared to just before the bounce? How do you know if the momentum associated with each was different after the bounce, and where did the momentum go or where did it come

5. When the basketball reached the floor, a collision occurred between it and the ground. Was the collision elastic or inelastic? How do you know? 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 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.