2. Types of Simple Machines
Part 3
Types of Simple Machines

3. What is a machine?
A machine is a device, like a bicycle, with moving parts that work together to accomplish a task.
All the parts of a bicycle work together to transform forces from your muscles into motion.

4. The concepts of input and output
Input includes everything you do to make the machine accomplish a task, like pushing on the bicycle pedals.
Output is what the machine does for you, like going fast or climbing a steep hill.
The input and output may be force, energy, or power.

5. Simple machines
A simple machine is an unpowered mechanical device that accomplishes a task with only one movement.
For example, a lever allows you to open a paint can, sweep the floor, or move a heavy rock.

6. Simple machines
A gear is a rotating wheel with teeth that receives or transfers motion and forces to other gears or objects.
A lever is a stiff structure that rotates around a fixed point called a fulcrum.

7. Machines within machine
Most of the machines we use today are made up of combinations of different types of simple machines.
For example, a bicycle is a complex machine made up of simple machines.
A bicycle uses wheels and axles, levers (the pedals and kickstand), and gears.
If you take apart a complex machine such as a clock, a food processor or blender, or a car engine, you will find it is made of simple machines like gears.

8. Machines do work
A simple machine does work because it applies a force over a distance.
If you are using the machine, you also do work, because you apply force to the machine to make it move.
By definition, a simple machine has no source of energy except the immediate forces you apply.
That means the only way to get output work from a simple machine is to do input work on the machine.

9. Output and input work
The output work done by a simple machine can never exceed the input work done on the machine.
In a perfect machine the output work exactly equals the input work.
There are no perfect machines.
Friction always converts some of the input work to heat and wear, so the output work is always less than the input work.

10. Machines have efficiency and power
The efficiency of a machine equals output work divided by input work multiplied by
For a perfect machine, efficiency is 100%.
A bicycle is a highly efficient machine at 95%, but the human body is relatively inefficient at 8%.
Power is how quickly work is accomplished.

11. Machines multiply forces
A rope and pulley system, for example, allows you to lift more weight (force) than you could lift on your own without a machine.
In other words, the rope and pulley system multiplies force.
To compensate for multiplying force, you need to apply it over a greater distance than when the output work is done.
For example, to multiply force from 5 newtons to 10 newtons and to lift the weight by 1/2 meter, you need to pull the rope twice as far as the weight is lifted—you need to pull 1 meter of rope.