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# Chapter 8

### Work and Machines

Term | Definition |
---|---|

Work | The transfer of energy to an object by using a force that causes the object to move in the direction of the force. |

Joule | The unit used to express energy: equivalent to the amount of work done by a force of 1N acting through a distance of 1m in the direction of the force (symbol, J). |

Power | The rate at which work is done or energy is transformed. |

Watt | The unit used to express power; equivalent to joules per second (symbol, W). |

Machine | A device that helps do work by either overcoming a force or changing the direction of the applied force. |

Work input | The work done on a machine; the product of the input force and the distance through which the force is exerted. |

Work output | The work done by a machine; the product of the output force and the distance through which the force is exerted. |

Mechanical advantage | A number that tells how many times a machine multiplies force. |

Mechanical efficiency | A quantity, usually expressed as a percentage, that measures the ratio of work output to work input; it can be calculated by dividing work output by work input. |

Lever | A type of simple machine that consists of a bar that pivots at a fixed point called a fulcrum. |

Pulley | A type of simple machine that consists of a wheel over which a rope, chain, or wires passes. |

Wheel and axle | A type of simple machine consisting of two circular objects of different sizes; the wheel is the larger of the two circular objects. |

Inclined plane | A type of simple machine that is a straight, slanted surface, which facilitates the raising of loads; a ramp. |

Wedge | A type of simple machine that is made up of two inclined planes that moves; often used for cutting. |

Screw | A type of simple machine that consists of an inclined plane wrapped around a cylinder. |

Compound machines | A machine made of more than one simple machine. |

Created by:
Kenmore Science