**Watt:** | S.I. unit for power; equivalent to joule/sec. |

**Wavelength:** | The distance between the two nearest points on a wave, which are in the same phase or the distance between two adjacent crests or two adjacent troughs. |

**Wave motion:** | The movement of a disturbance from one part of a medium to another involving the transfer of energy but not the transfer of matter. |

**Wave period:** | The time required for two successive crests or other successive parts of the wave to pass a given point. |

**Wave velocity:** | The distance traveled by a wave in one second. |

**Weight:** | The force with which a body is attracted towards the center of the earth. The weight of a body of mass m is given by mg, where g is the acceleration due to gravity. |

**Weightlessness:** | The state when the apparent weight of a body becomes zero. |

**Wien's displacement law:** | For a black body, the product of the wavelength corresponding to maximum radiance and its absolute temperature is constant. |

**Work:** | Work is done when force acting on a body displaces it. Work = Force x Displacement in the direction of the force. |