Centre of Gravity

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Centre of Gravity
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Centre of Gravity (C.G.)

• Definition
• Finding C.G. of an irregularly shaped thin piece
  of card

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Definition

• The Centre of Gravity (C.G.) of a body is the
  point through which the whole weight of the body
  seems to act
• For a regular object, the C.G is always at the
  centre

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We can think of the uniform bar as being made up
of a lot of tiny particles. Each particle will
have a force of gravity pulling it downwards.
(weight) The bar will balance at one particular
point, P, where the sum of all the clockwise
moments of the individual forces is equal to the
sum of all the anticlockwise moments of the
individual forces.
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The effect will be the same as if we had a single
force acting downwards at P. So we can think of
the gravitational force on the bar as a single
force acting downwards at P. The point, P, is
called the centre of gravity of the bar
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Finding C.G.

• If a body is hanging freely at rest, its centre
  of gravity is always vertically below the pivot.

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When the card is released, the weight of the card
acts like a single force through the C.G. This is
balanced by an equal and opposite force the
reaction of the pin. If the C.G. is not directly
beneath the pin, the two forces will form a
rotating motion which will make the card swing
downwards until the C.G. is directly below the
pin. We then hang a plumb line in front of the
card and draw a vertical line downwards through
the pinhole. The C.G. lies somewhere on this
line, AB. We repeat this with the pin at a
different position and obtain a second line, CD.
Since the C.G. must lie on both lines, it is at
the point where the lines intersect.
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The Centre of Gravity (C.G.) of a body is the
__________________________________________________
__________________________________________________
________
For a regular object, the C.G is always at the
_________
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We can think of the uniform bar as being made up
of a lot of ____________________. Each particle
will have a force of gravity pulling it
downwards. (weight) The bar will ________ at one
particular point, P, where the ___________________
_ ____________________ of the individual forces
is equal to the __________________________________
________ of the individual forces.
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The effect will be the same as if we had a
________________ acting downwards at P. So we can
think of the gravitational force on the bar as a
single force acting downwards at P. The point,
P, is called the _____________________ of the bar
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When the card is released, the weight of the card
acts like a single force through the C.G. This is
balanced by an equal and opposite force the
reaction of the pin. ___________
__________________________________________________
__________________which will make the card swing
downwards until the C.G. is directly below the
pin. We then hang a plumb line in front of the
card and draw a vertical line downwards through
the pinhole. The C.G. lies somewhere on this
line, AB. We repeat this with the pin at a
different position and obtain a second line, CD.
Since the C.G. must lie on both lines, it is at
the point where the lines intersect.