1.25
1.25 Starter
31 October 2011
12:12
· Why doesn't the see-saw balance?
Explanation
· The perpendicular distance from the pivot is the same on each side
· But the force (weight) on the left is great
· So the moment (turning force) on the left is greater
· The see-saw will rotate anticlockwise
1.25
Tuesday, July 06, 2010
3:04 PM
· 1.25 recall and use the principle of moments for a simple system of parallel forces acting in one plane
Principle of Moments
· When a system is balanced then the anticlockwise moments are equal to the clockwise moments
· This means that the anticlockwise turning force is equal to the clockwise turning force and the system doesn't move
Ma = Mc
Fa x da = Fc x dc
Ma = anticlockwise moment (Nm)
Fa = force causing the anticlockwise rotation (N)
da = perpendicular distance of Fa from the pivot (m)
Mc = clockwise moment (Nm)
Fc = force causing the clockwise rotation (N)
dc = perpendicular distance of Fc from the pivot (m)

