MOMENTS

Noadswood Science, 2013

MOMENTS

To be able to calculate moments

Tuesday, April 18, 2023

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

BALANCED Complete the moments

worksheet

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

CRANES Counterweights balance the crane

load armtrolley

loading platform

tower

counterweight

CRANE OPERATOR

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

MOMENTS

4. (10N x 2m) + (2N x 0.5m) – (35N x 1m) = -14Nm

There will be an anti-clockwise acceleration

5. See diagram below…