AQA GCSE Science

Investigating moments

Aims

In this activity, the mass of an object is measured using standard masses and a pivoted rule as a balance.

Safety

Remind the students to make sure the apparatus is stable and will not topple over.
A stand and clamp is provided to stop the rule turning too much.

Teaching notes

1Students may work in small groups in this investigation. Each group is asked to set the apparatus up as shown in the diagram.

2The stand and clamp near the end of the metre rule are provided to stop the metre rule toppling off the pivot. The metre rule should stay with its centre of mass on the pivot throughout.

3With the weights and object x suspended from the ruler, it should be possible to balance the beam horizontally, although it might move gradually from the horizontal position.

4Students may need to be taken through the theory of the experiment and the relationship between mass in kilograms and weight in newtons.

Answers to questions

1Each student’s results will depend on their own measurements. Ensure the correct unit is supplied with each numerical answer.

2If the centre of mass was not at the pivot, there would be an additional moment due to the rule to consider. As a result, when the rule is horizontal, the moment of the weights about the pivot would not be equal (and opposite) to the moment of x about the pivot.

3a 224mm

b0.16kg

cMore measurements of d2 could be obtained for the same distance d1, or the measurements could be made using a much greater value for d1to give a greater mean value for d2 , and therefore a more accurate value for the mass of x.

Technician notes

Students could work in small groups.

Equipment and materials

Metre rule
Suitable ‘pivot’, e.g. a short length of metal bar with a V-shaped cross section
Wooden block to support the pivot
Object of unknown mass, e.g. metal bolt, rubber stopper
3 × 1N standard weights and a 1N weight hanger
Two loops of thread
Stand and clamp (to stop the metre rule turning too much)

Setting up the experiment

The arrangement shown in the diagram is to be set up by the students working in small groups.

Safety

Remind the students to make sure the apparatus is stable and will not topple over.
The stand and clamp is provided to stop the rule turning too much and toppling over.