3Turn-3

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

• 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.
• 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.

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
• Pupils can also measure the force needed to open a cupboard door or the lab door. They need to ensure that the force meter is perpendicular to the door handle
• It's worth mentioning here the idea of selecting the right meter for the job. Using a sensitive meter will give a more precise result but the force may be greater than the highest scale reading.
• 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.

Plenary

Door challenge. An extension on the original strong person battle demonstrate how you can hold the door shut with a single finger if pupils push on the other side near to the middle. Warn them not to get their fingers to close to the opening and make sure they don't go too mad with their pushing. To rest your finger you can also use your foot.

Homework

Read pg 54 - 55 Answer qs on pg 55 - features work not covered yet

Additional Information

Resources Required

• Starter

1) Class set of metre rulers and 100g masses and holders (x12)

2) Large set square,

• 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

Safety/Hazards

Pupils to avoid dropping masses on feet

Notes

• None