Simple machines are the building blocks from which other, more complex machines are composed. 'Machines' has a technical meaning in this sense - a combination of rigid bodies formed to do one of three things:
- Alter magnitude of applied force.
- Alter direction of applied force.
- Change one form of motion or energy into another form.
Six Simple Machines
Most definitive lists of simple machines comprise the following six:
The lever - led to Archimedes boasting about moving the world.
The pulley - in combination with other pullies allows the trade-off of force and distance.
The inclined plane - first major application might have been dragging blocks to build the pyramids.
The wheel and axle - first invented about 5,000 years ago somewhere near the Black Sea, and now literally near every street corner.
The wedge - a double inclined plane.
The screw - a threaded cylindrical rod with a head at one end that can fasten two things together or apply power as in a clamp or jack.
Of the six, the lever, the pulley and the inclined plane are primary while the wheel and axle, the wedge and the screw are secondary. The reason for that is the wheel and axle is a rotary lever, the screw may be considered an inclined plane wound around a core and the wedge is two inclined planes stuck together.
A machine's mechanical advantage (MA) is the factor by which it multiplies an applied force. It is the ratio of output force to the input force applied to a machine. It would be nice if the two ratios were equal. That would make it simpler to calculate the ratio plus it would be called the ideal mechanical advantage (IMA). In any machine, some effort is used to compensate for friction, so the ratio of the resistance force to the effort1 is less than the IMA.
The efficiency of a machine measures how much friction and other factors reduce its work output from the theoretical maximum. A frictionless machine would have an efficiency of 100%, so a machine with a 25% efficiency operates at only one fourth of its theoretical maximum. Efficiency of a machine equals the ratio of its output divided by its input.
If anyone were to have a current patent on any of these machines they could pretty much charge what they like for industrial civilization to keep on going. Good thing no one does.