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Marshmallows in a Bottle
See how air pressure works
You will need:
- Marshmallows (small ones better)
- A Bottle (preferably a clear wine bottle)
- A bottle pump (the type that is sold for pumping the air out of half drunk wine bottles)
What to do:
Its very simple - put some marshmallows in the bottle and then start to pump the air out, stopping to shake the marshmallows occasionally. The air trapped in the marshmallows will expand as the air pressure in the bottle falls.
The pressure of the air above us at the surface of the Earth is usually about 1000mbar - thats 100,000Pa. That is the equivalent of between 2-4 (depending on the type) adult elephants on each m2! The air pressure varies between about 970-1040mbar as weather systems pass over. The pressure can also fall as you go up - either up a mountain (the air pressure at the top of Everest is only about 330mbar) or in an aeroplane (even though these can have artificially pressurised cabins, the air pressure can be lower than normal, usually the equivalent of being at 2500m above sea level).
Find out more:
About this experiment (with movie) at http://www.physics.org/interact/physics-to-go/amazing-marshmallows/index.html
Version if you'd dont't have a bottle pump: http://brightest-kidz.squarespace.com/journal/2008/4/9/marshmallows-under-pressure.html
The opposite experiment (requires specialised kit) http://www.stevespanglerscience.com/experiment/00000106
http://kids.earth.nasa.gov/archive/air_pressure/index.html
http://www.physicalgeography.net/fundamentals/7d.html
http://www.bbc.co.uk/weather/features/understanding/airpressure.shtml