MOMENTS Noadswood Science, 2013
MOMENTS Forces can make objects turn if there is a pivot
Think of a see-saw – when no-one is on it, the see-saw is level, but when someone sits on the end it tips
The see-saw can be balanced again if someone sits on the other end
Pivot
MOMENTS To work out moments we need to know: -
The force (weight) applied The distance from the pivot where the force is
applied
Moment (Nm) = Force (N) x Distance (m)
Pivot
MOMENTS
Force(F)
Moment(M)
Distance(D)
Force = Moment Distance Distance = Moment Force Moment = Force x Distance
To work out moments we need to know: - The force (weight) applied The distance from the pivot where the force is applied
Distance = perpendicular distance, r
MOMENTS
600N 300N
2m 2m
Anticlockwise moment = 600N x 2m = 1200Nm Clockwise moment = 300N x 2m = 600Nm Not balanced – anticlockwise moment
Clockwisemoment
Anticlockwisemoment
MOMENTS
500N 250N
1m 2m
Anticlockwise moment = 500N x 1m = 500Nm Clockwise moment = 250N x 2m = 500Nm Balanced!
Clockwisemoment
Anticlockwisemoment
MOMENTS
100N 700N
5m 3m
Anticlockwise moment = 100N x 5m = 500Nm Clockwise moment = 700N x 3m = 2100Nm Not balanced – clockwise moment
Clockwisemoment
Anticlockwisemoment
MOMENTS
300N 450N
3m 2.5m
Anticlockwise moment = 300N x 3m = 900Nm Clockwise moment = 450N x 2.5m = 1125Nm Not balanced – clockwise moment
Clockwisemoment
Anticlockwisemoment
BALANCING EXPERIMENT Balance a ruler on a pivot Add a mass at the end of the ruler Your task is to balance the ruler again, by adding 2x
masses to the other side Record the distance where they were placed
Now move your original mass, and repeat the experiment, recording your results
RESULTS
Force Distance from pivot
Moment Force Distance from pivot
Moment
1 2
1 2
1 2
1 2
1 2Moment (Nm) = Force (N) x Distance (m)
CRANES Why don’t construction cranes fall over?
Cranes have a concrete counterweight on the short arm, balancing the crane when it lifts a heavy load
MOMENTS Complete the moments higher worksheet…
1. A cross on the point of contact between the screwdriver and the rim of the paint tin (not the end of the screwdriver)
2. Move his hand further from the tin to increase the distance from the pivot, hence increasing the moment, or apply a bigger force (or both)
3. 0.10m x 35N = 3.5Nm