3-Sum1-B

Outcomes

• Pupils can identify the force, pivot and perpendicular distance to the pivot for a range of machines/tools and are able to calculate the moment in Nm.
• Pupils understand how the force and distance are related to the moment and can use the formula Moment = Force x perpendicular distance to pivot.
• Pupils are to understand the practical applications of changing the force and perpendicular distance for tools.

Specification References

• 1.15 recall and use the relationship between the moment of a force and its distance from the pivot:

moment = force × perpendicular distance from the pivot

Starter

• Here is a Moments Powerpoint to run along with the moments activities in this lesson.
• Pick two students out of the class to compete in a lifting competition. A strong rugby player and the smallest girl would be an amusing choice?? Ask the class who they think will be able to hold a 1/2 kg mass out in front of them for the longest? Give them each a metre rule but place the 1/2 kg mass at the end of the ruler for the stronger of the two and allow the weaker to hold the 1/2 kg mass 10 cm or so from their hand. This should open up some discussion.
• Now allow the class to experience this for themselves. In pairs, encourage them to change both the distance and the force.
• Using a large lever vary the distance to the pivot and use a set of masses to lift a very heavy object. From a range of readings get the student to predict how both the effort and perpendicular distance to the pivot is related to the moment or turning effect. Encourage a quantitative answer. If I double the weight of the heavy object what could I do to lift it? Double the weight or double the distance.
• Help the class derive the formula for moment and emphasise the idea of perpendicular distance. A large set square would help to visualise this.
• Have them determine the unit for moment.
• Change the arrangement by placing the 'heavy object' on the same side as your effort. Ask the pupils how you would lift the object now. Introduce direction by discussing if the 'heavy object' has a clockwise or anticlockwise moment. What direction does the moment for your effort have? It is important that the pupils understand that the effort and load could both be on the same side as the pivot.

Main Body of Lesson

• Moment circus - Have the pupils circulate round the stations finding/calculating the moment for a range of tools. The 'effort' should be labelled with laminated arrows. Set squares and rulers can be given to help find the perpendicular distances. Here is a sheet for them to record their measurements. Moment Circus Sheet
• Extension Once pupils have made notes and practiced a few moments questions then they can investigate the principle of moments. Pupils investigate the principle of moments by varying the force and distance of masses on a balanced ruler. They can calculate and show that the clockwise moment equals the anticlockwise moment.

Homework

Read pg 54 - 55 Answer qs on pg 55

Additional Information

Resources Required

• Starter

1) Class set of metre rulers and 100g masses and holders

2) Large lever and pivot system to lift a very heavy object, large masses to counterbalance, large set square, thin rope tied in a loop, large Newtonmeter to lift one end of lever.

• Moments Circus- Set of 6 different tools with a 'force vector' labelled (made out of laminated paper with the 'effort' labelled in Newtons, rulers
• Experiment - Class set of rulers and masses for principle of moments

Textbook References

• None

Website References

• None

Notes

• None