AQA GCSE Balancing Moments

Balancing Moments

A moment is the turning effect of a force.

Moments can be anticlockwise, or clockwise.

Principle of Moments.

when an object is balanced, the total clockwise moment about a point is equal to the total anticlockwise moment

The object in this case in a static equilibrium because the anticlockwise moment is the same size as the clockwise moment the object does not turn.

Calculations using Principle of Moments

Moment, M = Force, F x distance,d

Anticlockwise moment = Clockwise moment

Force 1, F₁ x distance 1, d₁= Force 2, F₂ x distance 2, d₂

Lets draw these distances and forces onto a diagram!

Example calculation

Use the diagram below to answer the following question

Calculate the weight of the pink ball on the right hand side

F₁ = 300N, d₁ = 1.8m, F₂ = ? and d₂ = 2m

F₁ x d₁ = F₂ x d₂

F₂ = (F₁ x d₁)/d₂

F₂ = (300N x 1.8m)/2m = 270N

F₂ = 270N

Example question 2

Use the image below to answer the following question

Calculate the distance between the pivot and the centre of the purple ball

F₁ = 900N, d₁ = ?m, F₂ = 600N and d₂ = 2m

F₁ x d₁ = F₂ x d₂

_d1 = (F₂ x d₂)/F₁

d₁ = (600N x 2m)/900N = 1.33m

d₁ = 1.33m

Practice questions

1.State the principle of moments

2. Use the image below to answer the following questions.

Calculate the length of the distance between the counterweight on the left hand side and the pivot. This unknown distance has been marked on the diagram as ?m.

3. Use the image below to help you to answer the following question

The man has a clockwise moment of 190Nm. Both of his feet are equal distance from the pivot. Calculate the distance between the pivot and his left foot. This distance has been labelled as ?m in the diagram above.