Workshop: piston, spring and chain

What the experiment shows

The piston is a linear actuator with a 1 m stroke. The spring weight oscillates around its rest position and the chain of hinged links acts like a flexible rope.

How to run it

1. Run the example: the weight starts bobbing on the spring and the ball swings on the chain.
2. Press P — the piston rod extends; release it and it returns.
3. Change the spring stiffness k: the larger k, the faster the oscillation.

Questions to discuss

• How does the oscillation period depend on the weight’s mass?
• Why does a chain sag into a curve?

The science

A spring force F = −k·x pulls the weight back to equilibrium, so it oscillates with period T = 2π√(m/k). A chain is a set of links connected by hinges: each part pulls the neighbours and the whole chain takes the shape with the lowest potential energy.

Try it at home

Hang a weight on a rubber band and measure how the period changes with different weights. Hang a necklace by its ends — it forms a catenary curve.

What to change in the editor

• Add more links to the chain.
• Give the piston another key.