Center Of Gravity

This lesson covers:

  1. What the 'centre of gravity' is
  2. How to find the centre of gravity for an irregularly shaped object
  3. How the position of the centre of gravity impacts the stability of an object

Centre of gravity

Diagram showing the centre of gravity for regular and irregular shapes, with weight acting at the centre for regular shapes and off-centre for irregular shapes.

The centre of gravity of an object is is the location where an object's weight appears to act. 


For uniform, regular shapes, like a square, this will be in the centre.


For irregular shaped objects or those with uneven densities, it will be off centre. 


Experiment: Finding the centre of gravity 

Illustration showing a retort stand with a freely hanging card shape, a pin, and a plumb line with a bob.

Method:

  1. Suspend the irregularly shaped object from a clamp stand.
  2. Attach a plumb line to the clamp stand.
  3. Mark the plumb line on the object using a pencil.
  4. Remove the object and suspend from a different point. Repeat steps 2 and 3.
  5. Repeat step 4 until a minimum of three lines have been drawn. 
  6. The centre of gravity is located where all lines cross.

How centre of gravity affects stability


An object's stability depends on its centre of gravity. By considering where the centre of gravity is located and how the weight acts on the object, we can determine if the object will be stable or unstable when tilted (i.e. whether or not it will fall over).

Diagram showing the centre of gravity and weight of an object, illustrating its stability.

An objects weight always acts vertically downwards from its centre of gravity.


If the weight acts within the base of an object, it is stable. 


Objects which have a wide base and a low centre of gravity are the most stable.

For which type of objects will the center of gravity be off center?

Objects that are stable

Objects with a wide base and low centre of gravity

Uniform, regular shapes

Objects with uneven densities

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What happens to the weight of an object when it is tilted?

The weight becomes lighter

The weight moves towards the pivot point

The weight increases

The weight remains in the same position

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What happens to an object when its weight no longer acts within the base?

The object becomes lighter

The object topples over

The object becomes more dense

The object becomes more stable

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What is meant by the centre of gravity?

A measure of how stable an object is

The point where the weight can be assumed to act from

The point where all the mass is

The centre of the object

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Which objects are most stable?

Objects with an even density

Objects with a wide base and a low centre of gravity

Objects with a high centre of gravity

Objects with a narrow base and a high centre of gravity

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