Forces are pushes or pulls. They can be balanced or unbalanced. If unbalanced they can change the shape of objects and change the way they are moving. Moments are turning forces.

Part of

This is an example of a common experiment used to investigate friction and should help you understand how to work scientifically.

To investigate the frictional forces on a mass being pulled down a slope of different gradients.

- Set up the apparatus as in the diagram.
- Pull the mass along the ramp using the force meter.
- Record the force needed to start the mass moving (this will be less than the force to pull it along once it is moving).
- Increase the height of the ramp to 10 cm to make the gradient steeper.
- Measure the force.
- Repeat by moving the ramp up in 10 cm intervals until 50 cm is reached.

- The
**independent**variable is the height of the ramp (its gradient). - The
**dependent**variable is the force needed to pull the mass down the ramp. **Controlled**variables include using the same mass and ramp surface.

Care must be taken with masses.

Height of ramp | Force needed |
---|---|

10 cm | 21 N |

20 cm | 16 N |

30 cm | 10 N |

40 cm | 5 N |

50 cm | 2 N |

The force needed to start the mass moving reduced as the ramp became steeper (the gradient increased). Fewer frictional forces exist when the ramp is steeper.

- Your measurements are
**accurate**if they are close to their true value. - Your measurements are
**precise**if they are similar when completed again. - Your experiment is
**repeatable**if you get precise measurements when it is repeated. - Your experiment is
**reproducible**if others get precise measurements when they repeat it.