Afternoon Experiment: Levitate Maltesers
By Mark Steer
As a student I spent a few happy hours learning how to levitate Maltesers an inch in the air before letting them drift down into my welcoming chops. It is the perfect activity for a lazy afternoon – you can deliver a short lecture on how your experiment demonstrates the problems faced by early jet engines whilst stuffing your face with chocolaty goodness.What to do
- Get a big box of Maltesers.
- Put your head back and start blowing out a steady stream of air straight upwards.
- Try to release the chocolaty treat into the centre of the air stream; with a bit of practice you’ll be able to keep it suspended for a good few seconds.
- Eat Malteser.
- Repeat ad nauseam.
What’s happened
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| The Coandă Effect Click to enlarge |
To imagine this better think of pouring cream out of jug. If you pour slowly then the cream will stick to the jug, dribbling down the side. Two forces are at work to make this happen. The first is surface tension, the cohesive force which causes molecules of the same type to stick together. The second is a bit more interesting, it’s known as the Coandă effect, after the Romanian aviation pioneer Henri Coandă.
In the 1900’s Coandă was experimenting with jet engines and had started to build the first jet aircraft. His new plane was finally finished in 1910, imaginatively named the Coandă-1910 and demonstrated to the world by its proud inventor. Unfortunately for Coandă he also ended up demonstrating that the flames from the back of his two jet engines didn’t shoot straight back as he had envisaged but stuck to the sides of the aircraft, completely ruining the aeroplane on its first, and only, flight. This tendency for moving air to wrap around objects is now known as the Coandă effect in memory of jet-powered flight's inauspicious beginnings.
The Coandă effect, which works just as well for air around a Malteser as it does for a jet exhaust over an aircraft, is caused by pressure differences as a gas passes around an object. As the stream of air tries to move away from the object is produces an area of low pressure which pulls the air back towards the object again. The result is that our Malteser becomes cocooned in the stream of air. This makes it easier for the chocolate to stay airborne.
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This experiment has been adapted from Mick O'Hare's excellent book How to Fossilise your Hamster see more at www.newscientist.com/hamster.
How about trying one of our other top tens:
This experiment has been adapted from Mick O'Hare's excellent book How to Fossilise your Hamster see more at www.newscientist.com/hamster.
How about trying one of our other top tens:
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- Top Ten Geek Holidays
- Top Ten Stupid Science Studies
- Top Ten Work-related Ills
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- Top Ten Weird Drinks
- Top Ten Grim Parasites
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