P3: Investigating principal of moments

Independent variable

forces applied to suspended metre rule

Dependent variable

distances from attached masses to pivot

Controlled variable

Apparatus

• Retort stand, boss-head and clamp

• G-clamp to clamp iron stand to bench

• 2 mass hangers and slotted masses up to 600 grams

• Uniform wooden metre rule

• Fine string

Method

1. Suspend and balance metre rule at 50 cm mark so it is in equilibrium

2. Using fine string, hang unequal masses, from either side of metre rule

3. Adjust position of masses until metre rule is balanced again

4. Record results in a table, and repeat for other loads/ distances

5. a force is trying to turn the metre stick anticlockwise/ clockwise

6. multiply force by distance to find their moments

Results

when metre rule is balanced the anticlockwise and clockwise moments are equal

Justification

principle of moments states, in equilibrium, total clockwise moment about a point equals total anticlockwise moment

Error

not balancing the metre rule correctly

Safety

• Clamp retort stand to the bench so it doesn’t fall

• Place an obstacle to prevent mass hangers falling on someone’s foot

• Safety glasses should be worn