What you need:
- Large clear jar with straight sides and a lid
- A few large beans or marbles
- Lentils or rice
What to do:
- Place a few large beans or marbles in the jar.
- Add lentils or rice to the jar until it is about half full.
- Place the lid on the jar and make sure it is on securely.
- Challenge a volunteer to make the beans or marbles move to the top of the lentils or rice.
- If they need some help, tell the volunteer to shake the jar up and down repeatedly. The larger items will make their way to the top, appearing to defy gravity!
The effect gets its name from the observation that Brazil nuts seem to make their way to the top of a jar of mixed nuts. More correctly termed ‘granular convection’ the effect is seen in other everyday situations, like in boxes of breakfast cereal.
Computer modelling of granular convection shows that smaller particles circulate in containers by moving up through the centre and downwards on the sides of the container. Larger objects move up through the centre, but do not move down the sides with the smaller objects.
The effect is seen in geology, with larger rocks rising up through smaller material, and has been used in astrogeology to explain the presence of large boulders on the surfaces of some asteroids.