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Overview of Machines
by Ron Kurtus (revised 27 June 2016)
A machine is a device that converts an external input into a greater output. It can also simply change the direction of the output. The input and output could be forces, distances, or speeds.
Machines usually consist of interrelated parts that combine to perform some kind of work, converting input energy into useful work. The input energy may be from humans, animals, engines or other sources.
Simple machines use a very basic configuration to do work. An example of a simple machine is a lever. A more complex machine is a an automobile.
Machines are used to create a mechanical advantage of the output force over the input force. Since there are losses in all motion, the efficiency of a machine is the output work over the input energy.
Questions you may have include:
- What does a machine do?
- What is mechanical advantage?
- What is the efficiency of a machine?
This lesson will answer those questions. Useful tool: Units Conversion
What a machine does
Machines can be used to cause the output force, output distance moved or output speed to be increased over the input.
Increasing force
There are situations where you want to move an object, but the resistance to that movement is greater than the force you have available. In such a situation, you might be able to use a machine to transform that force into one great enough to overcome the resistance.
A simple example of a machine is using a lever to lift a weight and overcome the force of gravity. According to the placement of the lever fulcrum, the input or effort force would be less the than that required to life the load.
Increasing distance
Sometimes you may want to move an object a greater distance than your input distance. A different configuration of a lever can increase the distance that the load is moved over the input distance.
Lever configuration results in load moving further than effort moves
Increasing speed
Wind turbines used for generating electrical energy are huge in size, but they rotate at a speed that is much slower than required to operating the electrical generator. Machinery consisting of shafts and gearing transform the input speed of rotation into a higher speed needed for the generator.
Mechanical advantage of a machine
The mechanical advantage of a machine relates to the increase in output over the input.
Typically, mechanical advantage concerns the increase in force through the configuration of the machine. In such a case,
MAF = FO/FI
where
- MAF is the force mechanical advantage
- FO is the output force
- FI is the input force
Note: MA is not M times A. Rather, it is an abbreviation for mechanical advantage.
There are situations where you may want to increase the distance or the speed that you move an object. In such cases, the distance mechanical advantage is:
MAD = DO/DI
and the speed mechanical advantage is:
MAS = SO/SI
A catapult is a good example of a machine that increases the output speed over the input speed of the force you apply.
Efficiency of a machine
The efficiency of a machine concerns how much energy is lost to friction and heat during its operation. Since work is the change in kinetic energy, the efficiency of a machine can be stated as the percentage of the output work divided by the input work.
Eff = WO/WI
where
- Eff is the efficiency decimal fraction
- WO is the output work
- WI is the input work
Multiply Eff by 100% to get the efficiency percentage.
But also, the output work equals the input work minus the losses due to heat and friction:
WO = WI − WLoss
Thus
Eff = 1 − WLoss/WI
(See Efficiency of Machines.)
Summary
A machine is a device that make moving an object against some resistance easier. It does this by changing the magnitude or direction of the input force. Most machines are complex, although there are machines consisting of a very basic configuration to do work.
Machines create a mechanical advantage of the output force over the input force. Since there are losses in all motion, the efficiency of a machine is the output work over the input energy.
Use science to make things more efficient
Resources and references
Websites
Machine - Wikipedia
Books
Top-rated books on Simple Machines
Questions and comments
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Overview of Machines