Moments (AQA GCSE Physics): Revision Notes

Worked Example: Balanced Seesaw

Imagine two children on a seesaw:

• Child A: 160N force, sitting 3m from the pivot
• Child B: 240N force, sitting 2m from the pivot

Step 1: Calculate the anticlockwise moment $\text{Anticlockwise moment} = 160\text{N} \times 3\text{m} = 480\text{ Nm}$

Step 2: Calculate the clockwise moment $\text{Clockwise moment} = 240\text{N} \times 2\text{m} = 480\text{ Nm}$

Step 3: Check for balance Since both moments are equal (480 Nm), the seesaw stays balanced and doesn't move.

Worked Example: Finding Unknown Weight

Problem: A 20N weight is 0.3m from a pivot, and it balances with an unknown weight 0.1m from the pivot. Find the unknown weight.

Step 1: Apply the principle of moments $20\text{N} \times 0.3\text{m} = \text{Unknown weight} \times 0.1\text{m}$

Step 2: Calculate the moment on the left side $6\text{ Nm} = \text{Unknown weight} \times 0.1\text{m}$

Step 3: Solve for the unknown weight $\text{Unknown weight} = \frac{6\text{ Nm}}{0.1\text{m}} = 60\text{N}$