“Bouncing Light”
Student Learning Objective:

Model light reflection with a tennis ball
Materials (per team):
1 Flashlight with batteries
1 Flat Mirror
1 roll Masking Tape
1 Tennis Ball
Introduction:
The law of reflection states that the angle of the incident (incoming) light rays and the angle of
the reflected (leaving) light rays are the same; that the angle at which the incoming light ray hits
a surface and the angle at which the light leaves the surface are the same. If the surface is
smooth and flat, like a regular mirror, the light rays will leave the surface parallel to each other;
this is called specular reflection. However, if the surface is irregular, the light rays will leave in
various directions; this is called diffuse reflection. The light bounces from the reflective surface,
and the direction the bounced light travels depends partially on the surface.
Preliminary Questions:
A. How would you define reflection to your friend?
B. What is a photon?
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Class Procedures:
Your team will be observing light from a flashlight in a dark room.
1. Obtain all of your materials and make sure your flashlight works.
2. Stand against a wall, and then take three large steps forward. Shine the flashlight toward the
wall.
3. Once your teach turns off the lights, observe the light from the flashlight and compare the light
in the air to the light on the wall. Record where the most light is seen, in the air or on the wall.
Team Procedures:
Your team will be observing the path of a light ray and mimicking this path with a tennis ball.
4. Read all team procedures (5-9) before you begin any experimenting. Then carefully read each
step as your team completes this activity. Take turns, alternate, using the materials and making
observations.
Warning: There will be mirrors on the floor; be careful not to step on them.
5. Stand against a wall, and then take one large step forward. Place the mirror in front of your
feet. Then move out of the way.
Mirror
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6. Stand on the other side of the mirror, and shine the flashlight toward the mirror. Use a piece
of masking tape to mark the location where the reflected light hits the wall. Then experiment
with the angle of your flashlight. If you change the angle of the flashlight, the angle of the
incoming light, if the bounced light still centered on your piece of masking tape? Record your
observation.
7. Think of a square. Have four people on your team form a square with 1-2 steps between each
of you at the corners. Have one person hold the mirror. Then have the person to the left of the
mirror shine the flashlight toward the mirror, changing the angle of the flashlight until the light
bounces from the mirror to the person who is to the right of the mirror. The fourth person should
observe that the incoming light angle and the outgoing light angle are the same.
The Bounce
8. Design Challenge:
Your goal is determine where you need to stand and at what angle you need to bounce the tennis
ball on the floor to have the tennis ball bounce to the piece of tape that you have on the wall.
Have each person on your team attempt this. Sketch a model of where the person throwing the
tennis ball needs to stand, the angle the tennis ball should be thrown, the path of the tennis ball
from you to the floor to the wall.
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9. Clean up:


Remove the tape from the wall and place it in the trash.
Return all materials to their designated place.
Analysis & General Questions:
1) Why is more light seen on the wall than in the air when you shine a flashlight toward a wall?
2) Based on your observations and model for the tennis ball, is the angle of the bounce from you
to the floor the same as the angle of the bounce from the floor to the wall?
3) Is the tennis ball more like a light wave or a light particle?
4) Did you observe primarily parallel or diffuse reflection as you experimented with the
flashlight and with the tennis ball? Explain your evidence.
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