Moments

Moments in Physics (Turning Forces)
A moment (or torque) is the turning effect of a force around a pivot (fulcrum). It is a key concept in mechanics, especially when analyzing levers, gears, and rotational motion.

The following diagram gives the formula for moments:
Moment = force × perpendicular distance from the pivot.
Scroll down the page for more examples and videos.
 

The moment of a force is calculated as:
Moment = Force × Perpendicular Distance from Pivot
τ = F × d or
M = F × d
Symbol:
τ (tau) or M
Units: Newton-meters (Nm)
Direction: Clockwise or anticlockwise.

Key Concepts

1. Perpendicular Distance Matters
   Only the perpendicular component of the force contributes to the moment.
   If the force is at an angle (θ):
   τ = Fdsinθ
   

2. Principle of Moments (Equilibrium)
   For an object to be balanced:
   Sum of clockwise moments = Sum of anticlockwise moments

Videos

Moments
Describe what is meant by a moment.
How to calculate moments using the perpendicular distance?

• Show Video

Balanced Moments
Describe what is meant by a balanced moment.
How to use the idea of balanced moments to calculate either the force or the distance from the pivot.
Use the idea of moments to explain why unbalanced objects topple.
Examples:

1. Person B is applying a force of 350N and is 0.76m from the pivot. Person A is applying a force of 500N. Calculate the distance that person A must sit from the pivot for the seesaw to be balanced.
   
2. The crane is used to lift a load which is 30 m from the pivot. The downward force applied by the load is 5000N. Calculate the downward force applied by the counterweight which is 10 m from the pivot.

• Show Video

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