Mass and Inertia

 

 
11.4  Mass and Inertia
 

1. Mass: the quantity of matter in an object

  • S.I. unit = kilogram (kg)
  • Mass of an object is constant if the quantity of matter in an object does not change

2. Inertia: the natural tendency of an object to resist any change in its original state, whether at rest or in motion

  • Cannot be measured

3. Newton's First Law of Motion states that an object will remain in its original state, that is, being at rest or in motion with constant speed if no external force acts on it

4. The inertia of an object is affected by its mass

  • The larger the mass of an object, the larger the inertia of the object
  • The smaller the mass of an object, the smaller the inertia of the object

5. Effect of inertia in daily life

 
Positive effect
  • The loose head of a hammer can be tightened by banging its handle against a hard surface
  • A wet umbrella can be dried by spinning the umbrella quickly
Negative effect
  • Can cause injury to car drivers
  • During landing, an aeroplane cannot stop within a short distance