Machines and Work

Science, Grade 6


Table Of Contents: Machines and Work

1. What Is a Machine?
A machine is a device that is designed to make work easier. Machines are not necessarily complex. For example, shovels and hammers are types of simple machines.
2. Input and Output Forces and Work
Work is done when a force causes an object to move. The work you do on a machine is called work input, and the force you exert is known as input force. The work the machine does is called work output, and the machine’s force exerted on an object is known as output force.
3. Calculating Work Input and Output
The input force times the input distance equals the work input. Similarly, the output force times output distance equals work output. The work output of a machine will never be greater than the work input.
4. How Machines Make Work Easier
Machines don’t change the amount of work that is done, but they do make work easier. A machine can help us by changing the size or the direction of the input force, or both.
5. Decreasing Input Force
Some machines make work easier by allowing us to exert a smaller input force, while achieving a greater output force. To do this, the input force must be exerted over a greater distance. For example, when loading a heavy box onto a truck, it is easier to push the box up a ramp than to pick it up. Pushing the box requires less input force, but it is applied over a greater distance.
6. Increasing the Input Force
Some machines make work easier by allowing us to exert a greater input force over a shorter distance, in order to achieve a greater output distance. For example, when using a hammer, you exert a large amount of input for a short distance on the handle, while the head of the hammer exerts a smaller output force that is applied over a greater distance.
7. Changing the Direction of the Force
For some machines, the direction of the exerted force is changed, while the input and output forces and distances remain equal. In these machines, changing the direction makes it easier to accomplish the work. For example, a pulley allows us to lift an object by pulling down on a rope rather than having to lift the object up.