Particle model of reflection

Demonstration

Both particles and waves reflect in the same way as light.

Apparatus and Materials

For the class

• Glass block
• Bouncing ball
• Marble
• Paper, white
• Carbon paper, soft

Health & Safety and Technical Notes

Read our standard health & safety guidance

The block may be so massive that it does not move on collision. If not, place a large weight behind it or fix it to the bench with a G-clamp.

Procedure

1. One student bounces a ball on the floor, at various angles, across a short distance to a partner. The paths before and after collision are in a vertical plane.
2. A student rolls a marble along a table (in a horizontal plane) to gently bounce against a vertical surface of a glass block. Repeat the experiment at different angles of incidence.

Teaching Notes

• Introduce these quick and simple experiments by asking,
• "Do particles reflect in the same way as light?"
• In step 2 you can record the path of the marble before and after hitting the wall by placing a sheet of carbon paper over a sheet of plain paper on the table. Ask students look for a pattern in the angles. It is easy to see the symmetry of the situation, even if angles of incidence and reflection are not mentioned.
• After they have done the experiment, ask students to remember (from experimenting with a ripple tank) how waves behave on reflection.
• Both particles and waves reflect in the same way as light.

This experiment was safety-tested in February 2006