Mass

Mass is a measure of the quantity of matter in an object at rest relative to the observer

• Mass is a scalar quantity

• The SI unit for mass is the kilogram (kg)

• Consequently, mass is the property of an object that resists change in motion

  • The greater the mass of an object, the more difficult it is to speed it up, slow it down, or change its direction

• A mass may sometimes be given in grams (g)

  • 1000 g = 1 kg

  • 1 g = 0.001 kg

Weight

Weight is a gravitational force on an object with mass

• Weight is a force, so it is a vector quantity

• The SI units for force are newtons (N)

• Weight is the effect of a gravitational field on a mass

• Weight is defined as:

The force acting on an object due to gravitational attraction

• Planets have strong gravitational fields

  • Hence, they attract nearby masses with a strong gravitational force

  
  

• Because of weight:

  • Objects stay firmly on the ground

  • Objects will always fall to the ground

  • Satellites are kept in orbit

The weight of a body is equal to the product of its mass (m) and the acceleration of free fall (g)