What you need:
- A wine glass
- A flat metal lid or plate
- 1 bag of dried peas
What you do:
- Fill a wine glass as far as possible with dried peas.
- Slowly pour water to the top of the glass to fill any remaining space in the glass.
- Place the glass on a metal plate or lid.
- Watch (and listen!) as the heap of peas grows slowly higher and higher. Finally a clatter of falling peas begins, which lasts for hours.
- Try several plates of different sizes, materials, and thicknesses for different sounds. Also, try other dried foods instead of peas. Which work the best?
What happened?
The peas swell and spill over the cup because of osmosis. Osmosis is the transfer of water through the cell membrane (the outside layer) of a cell. The water in the glass enters the cells and forces the cells - and the entire pea – to swell. There is no room left in the jar, but the peas have to go somewhere, so they go up, up, and away!
Plants need water to live, and they get all their water through osmosis. If there isn’t enough water, they wilt and shrivel up like raisins.
Animals use osmosis within their bodies, too. You may have noticed that after a long bath, your fingers seem shriveled like raisins, but in fact, they are all puffed up in some places more than others. Lots of the water from your bath has entered your skin and only leaves when you get out of the bath into the dry air, where the water can evaporate.
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