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Centre of Mass

Physics: AQA A Level, topic 4.1.5

Centre of Mass

Although the mass of an object is spread out across its body, it is possible to find a single point where all of the mass appears to be. This point is called the object’s centre of mass.

All in a single point

All in a single point

  • The centre of mass is the point through which an object’s weight appears to act.
Hanging objects

Hanging objects

  • If an object is hung from a string, it will hang with its centre of mass directly below the point that it is hung from.
Toppling over

Toppling over

  • An object will fall over if its centre of mass is outside its base.
  • An object will fall off a surface if its centre of mass isn’t over the surface.
Uniform solid

Uniform solid

  • The centre of mass of a uniform, regular solid will be at its centre.
  • We know this by symmetry.

Centre of Mass - Example

The dog remains upright because he keeps his centre of mass over his legs.

Balancing two legged dog

Test yourself on Centre of Mass

  • When will an object topple?

  • Which of the following are true of an object's centre of mass?

  • The centre of mass...

  • Why shouldn't lots of people stand on the top deck of a bus?

  • When will an object fall off a surface?

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