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# Bumper Balls

So now you’re the Chaos master of all.
Then it’s time to follow the bouncing ball.

Items You May Need:
tape, measuring tape, 1 friend

Challenge: A course with symmetry.

Hint: Use tape to help you mark the middle of the course and the middle of the framework. Line up the pieces of tape before you attach the track to the framework.

Here’s What To Do:

1. Build both frameworks. Set them 3 feet apart on the floor like this:

2. Now it’s time to work on track. The course has 7 pieces of track: long straight, short straight, flex, long straight, flex, short straight, long straight. Connect them as shown above.

3. Turn the course upside down. Use a measuring tape to measure its length. Divide that distance by 2 to find the center point and put a pieced of tape over that sport. Then turn the course right-side up.

4. Now measure the distance between the two boxes in the framework. Divide that distance by 2 to find the center points. Tape the framework to the floor at the center point and mark the center point.

5. Place the track in position on the framework. Line up the two pieces of tape that mark the center points of the track and the framework. Then attach the track to the adjustable supports. Make sure both clips on each adjustable support are attached to the track.

6. Now adjust the angle of the adjustable supports so that the rack looks symmetrical. One side should look like a mirror image of the other side. (Your protractor should help here. First measure the angle formed by the flex on the left side of the track and the floor. To match the angle formed by the flex on the right side of the track and the floor, you’ll have to move to the back side of the flex on the right, then read the angle.)

7. You’re done building. Now you’re going to complete five short experiments. For each experiment, there is a data table below. You will use the data tables to record observations, make predictions, and make notes for an experiment of your own.

NOTE: You won’t use Balls E and F in the five experiments on the following pages, but you may want to use them for additional experiments you try later.

Experiment 1: Place a ball (Ball B) in the center of the track.. (You’ve already marked the center with tape.) Have a friend place another ball at one end of the course (Ball A) and then release it.

Try this experiment twice. Record your data in the table below. For each trial, check all the columns that apply to each ball.

 Behavior of the ball after the collision Stayed in place Rolled a little Rolled away Bounced Trial 1 Ball A Ball B Trial 2 Ball A Ball B

Experiment 2: Place a ball (Ball B) in the center of the track. Place your finger on it and keep it there. When you’re ready, you will have a friend place a ball at the end of the course (Ball A) and release it.

Before you try this experiment, predict what will happen to the balls:

Now try this experiment twice. (On the second trail, press down hard on the stationary Ball B.) Record your data in the table below. For each trail, check all the columns that apply to each ball:

 Behavior of the ball after the collision Stayed in place Rolled a little Rolled away Bounced Trial 1 Ball A Ball B Trial 2 Ball A Ball B

Experiment 3: Place two balls in the center of the track. (Balls C and B). Place your finger on the one to the right (Ball B) . When you’re ready, you will have a friend place a ball at the end of the course (Ball A) and release it.

Before you try this experiment, predict what will happen to the balls:

Now try this experiment twice. Record your data in the table below. For each trail, check all the columns that apply to each ball:

 Behavior of the ball after the collision Stayed in place Rolled a little Rolled away Bounced Trial 1 Ball A Ball B Ball C Trial 2 Ball A Ball B Ball C

Experiment 4: Repeat Experiment 3, but this time place your finger on the ball to the left (Ball C). When you’re ready, you will have a friend place a ball at the end of the course (Ball A) and release it.

Before you try this experiment, predict what will happen to the balls:

Now try this experiment twice. Record your data in the table below. For each trail, check all the columns that apply to each ball:

 Behavior of the ball after the collision Stayed in place Rolled a little Rolled away Bounced Trial 1 Ball A Ball B Ball C Trial 2 Ball A Ball B Ball C

Experiment 5: Repeat Experiment 3 using three balls in the center of the course (Ball D, C, and B). Place your finger on Ball B. When you’re ready, you will have a friend place a ball at the end of the course (Ball A) and release it.

Before you try this experiment, predict what will happen to the balls:

Now try this experiment twice. Record your data in the table below. For each trail, check all the columns that apply to each ball:

 Behavior of the ball after the collision Stayed in place Rolled a little Rolled away Bounced Trial 1 Ball A Ball B Ball C Ball D Trial 2 Ball A Ball B Ball C Ball D

What do you think is causing the balls to do what they did in each experiment? How could you test your ideas in new experiments?

In just five experiments, you created a wide variety of collisions with many results. You probably didn’t find all the categories of movement you needed to describe what you observed.

#### Experiment 1:

At first, you might predict that something very simple will happen. What does happen is that some energy is transferred from Ball A to Ball B. If all of the energy in Ball A were transferred to Ball B, Ball A would have to stop. Why? Because energy is conserved. So the kinetic energy (energy of motion) of Ball A must drop to zero if Ball B moves away at the same speed. In practice, some of that energy is lost to heat and sound.

#### Experiment 2:

You may be surprised that Ball B scoots away from under your finger the first time. If you pressed down harder the second time, then Ball A bounced off of Ball B. Why?

Remember Newton’s Third Law of Motion – for every action there is an equal and opposite reaction. When Ball A strikes Ball B, Ball B pushes back on Ball A with an equal force. That force causes Ball A to reverse direction – a bounce.

#### Experiment 3:

Surprise! You probably thought Ball A would bounce just as it did in Experiment 2. But the kinetic energy found its way to Ball C, even though you were pressing hard on Ball B! Think about that next time someone pushes you into someone else in the lunch line.

#### Experiment 4:

Something very curious happens in this experiment. If you were observing carefully in Experiment 2, you may have seen it there as well. In Experiment 4, Ball A stops moving forward, but it does not stop moving – it continues to spin. You probably don’t think of any ball on the track spinning (rotating) as it moves along the track, but it does.

#### Experiment 5:

You probably had to try this experiment more than twice to observe everything that was happening. When Ball A strikes Ball B, Ball C and Ball D roll away – at different speeds. Ball D begins to roll up the incline on the other side of the course, slows, appears to stop, and then begins to roll back toward Ball C. On its return, Ball D strikes Ball C and stops dead, sending Ball C to collide with Ball B. When Ball C strikes Ball B, Ball A begins to move away from Ball B.

So what’s happening here? The energy of Ball A’s motion is transferred through Ball B to Ball C. But Ball C does not transfer all of that energy to Ball D. How do you know? Ball C moves! You can tell it has less energy of motion than Ball D though, because it moves away more slowly than Ball D does.

Ball D moves away until its motion is slowed and then reversed by gravity – Ball D actually begins to climb the incline! On its return, Ball D transfers all of its kinetic energy to Ball C. (You know this because Ball D stops dead in its tracks, or should we say track.) Ball C transfers its kinetic energy to Ball B, which transfers it to Ball A. Why doesn’t Ball A move back up to where it started? For that matter, why doesn’t Ball A move at least an equal distance to that of Ball D? The answer to both questions lie in the other forces which tend to oppose all of the motions you observe in the Chaos toy – especially friction.

Build With It!

You can use what you learned from Bumper Balls in your own projects. You’re now an expert on any course where two balls will collide!

Easy Variations:

1. Try Experiment 1 with two balls in the center of the track.

2. Try Experiment 1 with additional balls in the center of the track.

3. Try Experiment 5 with four or five balls in the center of the track.

4. Build a longer course.