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Saturday, September 13

Simple Machines

Every mechanical device, even the most complicatrd giant earthmover, is made from only four different types of simple machines. These are the lever, the inclined plane or ramp, the wheel and axle, and the pulley. The lever ia a stiff beam or bar that pivots at point called fulcrum. If the fulcrum is closer to one end than the other, you can use the lever to lift a heavy weight more easily. The inclined plane (ramp or slope) is a machine to. It is usually easier to slide a heavy weight up a slope than to lift it straight up. Place two inclined planes back-to-back and they form a wedge, as in a knife blade, axe or chisel. A wedge wrapped around a rod, in the corkscrew-like shape called a helix, forms a screw. Screws are used to lift things and fasten them together.

Building the pyramids
The pyramids were built in ancient Egypt about 4,500 years ago, from thousands of blocks of stone-some weighing many toones. These may have been levered into place, or dragged up a slope built beside the pyramid, or rolled up on logs. No-one really knows.


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