investigation of the laws of equilibrium for a set of coplanar forces the professional development...
TRANSCRIPT
Investigation of the laws of equilibrium for a set of
coplanar forces
The Professional Development Service for Teachers is funded by the Department of Education and Skills under the National Development Plan
T.H.
Method
• Find the centre of gravity of the metre stick• Find the mass and hence the weight of the
metre stick• Set up the apparatus as in the photo• Use a spirit level to ensure the apparatus
is horizontal• Record each weight with its position
(include the weight of the metre stick acting at its centre of gravity.)
Balance the metre stick on a straight sharp edge e.g. a protractor and record its centre of gravity. Here, the centre of gravity is at the 502 mm mark.
Why isn’t the centre of gravity at the 500 mm mark?
• One of the ends of the metre stick might be slightly damaged.
• The material from which the metre stick is made might not be uniform.
Why does the metre stick have to be horizontal?
• The weights act vertically downwards.
• We calculate the moments by multiplying each weight by the perpendicular distance from a reference point.
• If the metre stick is horizontal, these distances can be read directly.
• Otherwise, we would have to use trigonometry.
Record the forces and their positions
Note that there are five downward forces (including the weight of the metre stick),
and two upward forces.
The sum of the clockwise and the anticlockwise moments, to two significant
figures, is zero.
This verifies the second law.