3Turn-4

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

Starter

• Pupils to attempt principle of moments mini experiment with "rulers", pivots and small masses. Remind pupils the equation for calculating moment.
• Have pupils tabulate their results (see ppt). Give them 5-10 minutes to get some results and then discuss these with the group.

Main Body of Lesson

• Move onto the giant balance bar. You can give pupils a diagram of the bar so they can quickly record the what they see. Load up the bar with 2 sets of masses. Introduce the idea of checking answers with ratios (i.e. if a mass is twice as heavy then it needs to be half as far from the pivot to balance). Also talk about clockwise vs. anticlockwise in terms of direction. You should also mention that moments are vectors and their direction is important. Try a few examples and have pupils calculate where the 2nd weight would need to be placed or how heavy the second mass would need to be. Move onto 3 or 4 weight systems. Finally unbalance the beam and ask pupils what upward force you'd need to apply on the end to balance. This is a good place to talk more about clockwise and anticlockwise direction system. This could be done in books, on the sheet or on whiteboards.

Give pupils some notes on calculating how to balance a system and the idea of equilibrium. They should also have a statement about the principle of moments.

Plenary

Finish with a problem for next lesson. How could you use a set of masses to determine the weight of a clampstand. Have them brainstorm with their partner and maybe sketch out their diagram on a whiteboard. You could also set them the problem of why we can usually ignore the weight of a beam in a system (either very light compared to masses involved or it is placed on its centre of mass).

Homework

• Read pages 54-55
• Q 1-4 pg. 55

Additional Information

Resources Required

• pivots, "rulers", masses
• large principle of moments apparatus
• a large pivot and set of masses(for the weighing a clampstand discussion)

Textbook References

• None

Website References

• None

Skills Addressed

• Obtaining

Notes

• None