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

Review their finding from the principle of moments experiment.
Pupils will apply the principle of moments for a set of 4 example questions given here on a powerpoint. These can be set up on the large apparatus at the front of the class if you wish. Have the pupils work out the answers on the mini whiteboards and confirm the answers by using the apparatus. Principle of moment questions powerpoint

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.
The beam should remain horizontal. Discuss with the pupils how this could be done.

Group the class into 5 groups of increasing ability. There are three Moment Challenges of varing difficulty. 1) Measuring an unknown mass 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 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 solving it.
If there is time they can present their problem and how they solved it.

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

Moment Challenges

Problem 1 x 3 - rulers, pivots, unknown mass, known masses
Problem 2 x 4 - 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