This is the point, where all the mass of the object appears to be concentrated. Some objects can have this point outside the object.

Centre of Gravity

When an object is in a gravitational field .i.e. on Earth; it is the point through which, all the weight of the object, appears to act.

Usually the centre of mass and the centre of gravity are in the same place, but not always: We will consider that they are. From now on I will refer to the centre of gravity.

Centre of Gravity Of Regular Shapes

• The centre of gravity of a triangle is where the medians cross.

• The centre of gravity of a rectangle is where the diagonals cross.

• The centre of gravity of a circle is at its centre.

Centre of Gravity and Stability

If the line, through the centre of gravity of an object, falls outside the base of the object ; the object will fall over.

Look at these shapes:

If the triangle is tipped slightly, the line through the centre of mass, will stay within its base and so it will return to its original position. We say that the triangle is in stable equilibrium.

If the rectangle is tipped slightly, it will topple over. The rectangle is in unstable equilibrium.

If the circle is tipped it will roll. The circle is in neutral equilibrium. 

The position of the centre of gravity needs to be taken into account in the design of objects. A single rose vase is for one rose, otherwise it will topple over.

• Introduction
• Centre of Gravity and Sports
• Mechanics Index