The document discusses the centre of gravity of objects. It defines the centre of gravity as the point where an object's entire weight seems to act no matter its orientation. For regularly shaped objects of uniform thickness and density, the centre of gravity is at the geometric centre. Irregularly shaped objects require attaching a plumb line to determine where three lines drawn from holes intersect, which marks the centre of gravity. Stability can be increased by lowering an object's centre of gravity or widening its base. Examples given are a bus made stable by a low centre of gravity and a desk lamp stable due to a wide, heavy base.

1. Centre of Gravity
Presenter: Mr. D. Lawrence, MSc., B.Ed.

2. Centre of Gravity
 Centre of gravity is that
point in an object where
its entire weight
appears to be acting for
any orientation of the
object.

3. Centre Of Gravity Of Regular
Shaped Objects
 An object of uniform
thickness and density
has its mass evenly
spread throughout and
its centre of gravity is at
its geometrical centre.

4. Finding the centre of gravity of an object with an
irregular shape or non-uniform thickness and density

5. Finding the centre of gravity of an object with an
irregular shape or non-uniform thickness and density
 Procedures:
1. Make three small holes at the
edges
2. Put a strong pin through one of
the small holes and fix a clamp
so that the object can swing
freely.
3. Attach a plumb line (a length of
thread with a heavy mass on the
end) to the pin.
4. When the object and the
plumbline have both stopped
swinging, mark a cross on the
object exactly
behind the plumbline and near the
opposite edge to the hole.
5. Repeat this procedure in all
three holes
6. Remove the object from the pin
and draw straight lines with a
ruler from each hole to the
opposite cross.
 NB: The point where the three
lines intersect is the centre of
gravity of the object

6. Stability
Definition: The ability of an object to maintain
equilibrium or resume its original, upright
position after displacement.
Two of the methods that can be used to make
objects more stable are:
1. Lowering the objects centre of gravity
2. Widening the base of the object

7. Stability

8. Practical Application of the
Principle of lowing C.G.
 This bus is made more
stable(less likely to turn
over when going around
a corner) by keeping its
centre of gravity very
low. Light-weight
materials are used for
the construction of its
upper deck and its
chassis and engine are
mounted as low as
possible.

9. A Desk Lamp’s Centre Of Gravity.
 This desk lamp is made
very stable by its wide
and heavy base. Where
do you think its centre
of gravity is?