Circular Motion
Forces and Motion

Speeding Spinner

At home for 5-11 11-14

What you need

  • Two ball bearings
  • Large rubber band
  • Glue
  • Two paper clips


  1. Wind a paper clip into a spiral, tie one end of the rubber band to it and glue it to a ball bearing. Do the same with the other end of the band
  2. Holding one ball bearing, rotate the other until the band is wound up. Keeping the ball bearings together, drop them onto a smooth surface

Results and Explanation

The ball bearings spin, speeding up as the band unwinds. Then the band contracts, winding up the other way. The cycle repeats, with the bearings spinning in the opposite direction.
The twisting in the band makes both bearings turn, so they roll round. When the band has untwisted they're moving so fast that they overshoot, making the band wind up the other way, which slows them to a pause.

These experiments have not been specifically safety tested for home use but we believe them to be safe if the instructions are followed. Adult supervision or direction is recommended as appropriate. All experiments are carried out at your own risk.

Circular Motion
can be analysed using the quantity Centripetal Acceleration
can be described by the relation F=m(v^2)/R

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