Outcomes

Pupils apply the principle of moments for a balanced object.
Pupils investigate how the upward forces on a light beam varies with the position of a heavy object placed on the beam.

Specification References

1.25 recall and use the principle of moments for a simple system of parallel forces acting in one plane
1.26 understand that the upward forces on a light beam, supported at its ends, vary with the position of a heavy object placed on the beam

Pupils apply the principle of moments for a set of 3 example questions given here, one example will test the idea that the mass acts from the centre of gravity. Principle of moment example questions

Bridge Investigation - Pupils investigate how the upward force on a light beam (bridge) varies with the position of a heavy object (truck) placed on the beam. The set up has a forcemeter on one end and a sting hold the other end. The pupils should produce a graph on how the force varies with the distance to the end.

Group the class into 5 groups of increasing ability. There are three Moment problems of varing difficulty. 1) Measuring the unknown mass and determining its density 2) To find the mass of a retort stand using the principle of moments and 3) to find the centre of mass of a student.
Have two groups attempt activity 1, another two groups of higher ability attempt activity 2 and one group of highest ability can be challenged by activity 3. All three activities have cards explaining what they need to do and also have a Moments hint card to help groups who are stuggling.
They should be asked to read through the card and have a look at the equipment. They should then discuss the activity as a group and then go onto try solving it.
If there is time they can present their problem and how they solved it.

Class set of rulers suspended with a forcemeter from one end , large mass with body of truck over it, 1/2 meter rule

Moment problems

Problem 1 x 2
Problem 2 x 2- retort stand x2, hanging 100g masses x 2, pivot x 2, 1/2 metre rule x 2
Problem 3 x 1 - large plank for pupil to lie on, large fulcrum x 2, Newton balance, metre rule x 2