Mass & weight

Mass (m)


  • The mass of a body is the quantity of matter contained in it. 
  • Mass is a scalar quantity which has only magnitude but no direction.
  • Mass of a body always remains constant and does not change from place to place.
  • SI unit of mass is kilogram (kg).
  • Mass of a body can never be zero.

Weight (W)

  • The force with which an object is attracted towards the centre of the earth, is called the weight of the object.
    Now, Force =m×a
    But in case of earth,a=g
    But the force of attraction of earth on an object is called its weight (W).
  • As weight always acts vertically downwards, therefore, weight has both magnitude and direction and thus it is a vector quantity.
  • The weight of a body changes from place to place, depending on mass of object.
  • The SI unit of weight is Newton.
  • Weight of the object becomes zero if g is zero.

Weight of an Object on the Surface of Moon
Mass of an object is same on earth as well as on moon. But weight is different.

weight of the object on the moon = (1/6) × its weight on the earth.