1. Centre of gravity

2. Where is the centre of gravity of an object?
The Earth pulls every molecule of an object in a downward direction, or in other words every molecule in an object has a weight. We can add all these millions of tiny molecule weights together and get a single resultant force for the weight of the whole object.

3. An object behaves as if its whole weight was a single force which acts through a point G called its centre of gravity.
We define the centre of gravity of an object as the point through which its whole weight acts for any orientation of the object.

4. The centre of gravity, G, stays in the same position on the object.
The weight of the object always acts through G for all orientations of the object.

5. Activity

6. The centre of gravity of the lamina is the point of intersection of the first two lines drawn on it. The third line can be drawn to provide a check for accuracy.

7. If all three lines meet at one point, the experiment is accurate
If all three lines meet at one point, the experiment is accurate. If they do not, the accuracy may be judged by the area of the triangle formed by the three intersecting lines. The larger the area, the poorer is the accuracy.

8. What makes a body stable?

9. An object is said to be stable if it is steady or well balanced so that when it is pushed slightly it does not topple or fall easily.
Let us try to do a simple experiment or derive the conditions for stability.

12. Three states of equilibrium
Stable equilibrium
Unstable equilibrium
Neutral equilibrium

14. Conditions for stable equilibrium
The body should have a broad base
Centre of gravity of the body should be as low as possible
Vertical line drawn from the centre of gravity should fall within the base of support

15. How is this significant to real world scenarios?

19. Assessment
Determine the position of the centre of gravity for the object given
What state of equilibrium would the following bodies be in?
A standing fan
A rolling ball
A cone placed on its vertex

20. Explain how the position of a body’s centre of gravity affects its stability.
Identify one way in which this phenomena is applicable to your life. You should include a description of how the design and/or function of the object/body affects its stability.

21. Summary
Centre of gravity
Stability