Non-uniform acceleration with a ticker-timer

Class practical

Students can explore another kind of motion and its velocity-time graphs.

Apparatus and Materials

For each student group

• Lengths of loose chain (at least 1m long)
• Ticker-timer with power supply unit
• Ticker-tape
• Sellotape

Health & Safety and Technical Notes

An empty cardboard box on the floor to catch the chain should ensure that no one's foot is at risk.

Read our standard health & safety guidance

DIY and hardware stores sell lengths of chain.

Procedure

1. Put the length of chain on a smooth table so that it is at right angles to the edge. Then pull the end over the edge until, on release, the whole chain slides. Then the hanging portion will pull the rest, with increasing acceleration.
2. Repeat this with a length of ticker-tape attached to the chain.
3. Use the ticker-tape to create a velocity-time chart or graph.
4. Draw a smooth curve to fit the top-middle of each length of tape on the chart. Draw tangents to the curve at two points. Work out the gradients of the curve at each point, and so also the accelerations.
5. For an explanation of drawing ticker-timer acceleration charts see:

   Velocity-time graphs with a ticker-timer

Teaching Notes

• The acceleration of the chain depends on the force pulling the chain over the edge of the table. The force increases as the length of the chain over the edge increases.
• The experiment shows that acceleration is not always constant. In fact acceleration can change and itself have a rate of change. The rate of change of distance (or, more strictly, displacement) is called velocity. The rate of change of velocity is called acceleration. The rate of change of acceleration has no name so it's hard to get hold of the concept.
• It is interesting to investigate the motion of sets of chains with different mass/length ratios.

This experiment was safety-tested in January 2005