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A Radish Vacuum
You will need: A knife, radish, and saucer.
'Nature abhors a vacuum' and the outer air will always try to enter an area of lower air pressure. This physical law has been put to use many times in various pieces of machinery and equipment.
Possibly the vacuum cleaner is the best known of these machines. Vacuum cleaners may vary in size, shape and performance from maker to maker, but their basic principle is always the same: a vacuum-or at least an area of low pressure-is created by some means (usually electrical). The outer air is then allowed entry in such a manner that it will carry with it any loose dirt, fluff, etc., in its path.
When we press a little rubber suction device to the tiled wall of our bathroom, it is retained in position by air pressure and not by some form of invisible glue.
You can make your own simple form of vacuum sucker from an ordinary radish. Take a large, firm radish and cut it in half with a single stroke of a sharp knife. With the point of the knife scoop out some of the flesh of the radish to form a hollow in that half of the radish which bears the long root.
Now press the half of radish firmly into the center of a clean saucer.
Lift the radish by its root and you will find that the radish adheres so firmly to the saucer that it raises the plate from the table.
Air pressure is at work, of course. In cutting the radish with a single stroke of the knife you left a clean, flat surface. In scooping out a hollow in the middle of the radish you provided an air space. This air was completely expelled from the hollow when you pressed the radish half firmly against the saucer. The outer air tried to enter the vacuum created in the center of the radish, but the cut surface of the radish had joined in an airtight bond with the saucer. (This bond was further strengthened by juice squeezed from the radish when you exerted pressure to expel the air.) Air was unable to gain entrance and was left pressing down upon the outer surface of the radish, thus 'gluing' it to the saucer.
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