NEXT: , Marrara

Mexican Jumping Bean

Image of a hand holding a jumping bean made from foil

This bean may appear to move by magic, but the real reason is just marble-ous!

Australian Curriculum links

  • Science > Biological Sciences > Year 2 > ACSSU030
  • Science > Physical Sciences > Year 2 > ACSSU033
  • Science > Physical Sciences > Year 4 > ACSSU076
  • Science > Physical Sciences > Year 8 > ACSSU155
  • Science > Physical Sciences > Year 10 > ACSSU229

You’ll need

  • Scissors
  • Aluminium foil
  • Small marble
  • A whiteboard marker, or similar, with a diameter slightly larger than the marble
  • Rectangular lunchbox with lid

Try this

  1. Cut a piece of aluminium foil about 10cm x 6cm.
  2. Roll the foil around the whiteboard marker from the short side to make a 6cm long tube.
  3. Slide the tube slightly off the whiteboard marker, and close over one of the open alfoil ends.
  4. Slide the tube completely off the whiteboard marker and place the marble inside the hollow aluminium foil tube.
  5. Carefully close the open end of the alfoil tube to seal it. It’s ok if it looks a bit rough at this point, but the marble should be able to roll within the tube
  6. Put the bean in the rectangular lunchbox and shake it side to side. As the bean hits the wall, it will push on the aluminium foil and create round ends.
  7. Remove the lid of the container and gently roll the bean around to see it come alive!

Further investigation

  • Show the bean to someone who didn’t see you make it. Ask them to guess what is causing the movement. If they need a hint, give it to them so they can feel it.
  • Try rolling the bean along different surfaces. What surface is the best to roll the bean along?
  • What happens if you use several smaller balls, rather than a big marble?

What’s happening?

While the bean may look like it’s moving in a crazy way, it’s really just the rolling marble pushing the aluminium foil tube along. When you tip the bean, the marble rolls along the tube. When it reaches the end of the tube, the marble will try and keep rolling, but to do this it has to push the tube so that it flips over. Once the tube flips over, the marble can roll down the tube again and this pattern continues. The tube part of the bean may appear to flip magically, but it’s just the marble rolling along smoothly that causes it all.

On a high school level, the movement of the ‘bean’ illustrates Newton’s first law of motion – that an object at rest will stay at rest unless a force acts on it, and that a moving object will keep moving in the same direction, and at the same speed, unless a force acts on it. In other words, all objects resist changes to their state of motion. This idea is often referred to as inertia.

Real world links

Mexican jumping beans are real. The jumping bean moth lays eggs inside developing flowers of the plants. The eggs hatch and the larvae grow inside the hardened beans. The beans jump around because the larvae move inside the bean, somewhat like the marble inside the foil capsule.

Further information

  • Watch this clip from the BBC show “Weird Nature” on Mexican jumping beans and their strange behaviours
  • While you can order Mexican Jumping Beans online, they are not allowed to be imported or brought into Australia due to our strict biosecurity laws