Massive beam and anvil to show pressure exerted by a stream of balls

Demonstration

This is a larger, more dramatic version of:

Pressure exerted by a stream of balls

Apparatus and Materials

• Anvil and beam
• Marbles or 13 mm steel balls (not small steel balls)

Health & Safety and Technical Notes

Eye protection must be worn. The teacher must stand on a step-ladder to release the balls, not on a stool or on a bench.

Read our standard health & safety guidance

Construct a see-saw with a massive elastic anvil at one end. You can make a very good version by placing a sheet of about 13-mm Perspex on top of a massive steel block, with a thin layer of glycerine between them. Screw the Perspex into the steel near the edges.

The anvil should be placed on a large wooden beam, which is pivoted near that end. The pivot could be a steel rod, fixed to the beam, free to roll on supports at the side. The other end of the beam must carry a counterweight and a pointer to indicate deflections.

Place a large tray under the apparatus (or make a barrage around it) to catch the balls. (An inflatable paddling pool may be suitable.)

Procedure

Pour a stream of marbles or steel balls from as high as possible above the anvil and the see-saw shows there is a deflecting force on the beam.

Teaching Notes

It helps if there is a release mechanism so the marbles or steel balls fall vertically onto the anvil. This is not an easy demonstration to set up but it is impressive when working.

This experiment was safety-tested in March 2005