MACHINES
Our world runs on machines. They make work easier for us. A machine uses physical efforts, forces and work to get a job done. It can be as complicated as a jet engine or a combine harvester to gather crops. Yet it can be as simple as a crowbar used to lift heavy stones or a wheel on an old cart. Even the most complicated machines are combinations of a few kinds of simple machines.
The main kinds of simple machines are:
- Inclined plane A slope or ramp to drag or roll heavy objects upwards.
- Wedge Two ramps back to back as used in knife and axe blades.
- Lever A rigid bar or beam that pivots on a hinge or fulcrum, like a crowbar.
- Screw A wedge twisted into a corkscrew shape forces its way through a substance.
- Wheel and axle An endless curved ramp turning on its central point, the axle.
- Pulley A wheel with a groove in its rim for a rope, chain or cable.
These machines make tasks easier. But they do not give something for nothing. Usually the task takes longer and involves more movement, so the total work at the end is the same as doing the task without it.
Ancient structures like the Egyptian pyramids were built using simple machines such as ramps and rollers. The driving force came from humans. The ground drill or auger is a modern machine, an engine-driven screw.
A rope and pulley changes the direction of a pulling force. It is usually easier to pull down on a rope than to pull up. Loop the rope around two pulleys and it can lift a heavier weight than with one. But the rope must be pulled further. Adding more pulleys to the system makes the lifting even easier, but the rope has to be pulled yet further. The total work done to move the weight is the same in each case.
The lever is a stiff bar that pivots at a fulcrum. If the fulcrum is near one end then a small force at the other end moves a heavy weight but not very far.
Picture Credit : Google
