Stability is a measure of how likely it is for an object to topple over when pushed or moved.

Stable objects are very difficult to topple over, while unstable objects topple over very easily.

An object will topple over if its centre of gravity is ‘outside’ the base, or edge, on which it balances.
Two cars on their side
For an object to be stable it must have:
  • a wide base
  • a low centre of gravity

Objects with a wide base, and a low centre of gravity, are more stable than those with a narrow base and a high centre of gravity.

The yellow car has a wider wheel base and lower centre of gravity than the blue car.

It is more stable.

The wheel acts as the pivot for the car.

The weight has a turning effect or moment, which causes the car to topple over or fall back.

Cars on their side

A double decker bus is stable as it has a:

  • low centre of gravity because of its low, heavy engine and heavy bottom deck;
  • wide wheel base.
Traffic cone

A traffic cone is stable as it has a:

  • low centre of gravity G because of its heavy base;
  • wide base.