4-FAD-02
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Contents
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.
- Pupils can find the centre of gravity for a lamina using a pin and plumbline.
- Pupils can label the centre of gravity for a range of objects and can appreciate that it may not be located on the object itself.
- Pupils investigate and can apply the principle of moments for a balanced object.
- Pupils investigate how the upward forces on a light beam varies witht he position of a heavy object placed on the beam.
Specification References
- 1.23 recall and use the relationship between the moment of a force and its distance from the pivot: moment = force x perpendicular distance from the pivot
- 1.24 recall that the weight of a body acts through its centre of gravity
Starter
- Using a large lever vary the distance to the pivot and use a set of two 10kg and a 5 kg mass mass to lift a pupil. 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.
- Help the class derive the formula for moment and emphasise the idea of perpendicular distance.
Main Body of Lesson
- Moment circus - Have the pupils go round the stations finding the moment for a range of tools. The 'effort' is labelled with laminate arrows. Set squares can be given to help find the perpendicular distances.
- 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.
- Introduce the idea of centre of gravity. Have the pupils cut a lamina out of the card and use the pin and plumbob method to find its centre of gravity. Next hold up a range of objects and have the pupils predict where the centre of gravity is. End with showing a few more interesting centre of gravity senarios such as the balancing forks and match on the edge of a glass.
- 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 quesitons
- 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.
Plenary
- Group the class into 5 groups of increasing ability. There are three Moment problems of varing difficulty. 1) 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.
Homework
Additional Information
Resources Required
- Large lever and pivot system to lift a pupil+ 10 kg mass
- Class set of rulers and masses for principle of moments
- Class set of rulers suspended with a forcemeter from one end , large mass with body of truck over it, 1/2 meter rule
- Class set of card, scissors, retort stand, cork and pin, sting and plastecine.
- Set of 6 different tools with a 'force vector' labelled (made out of laminated paper with the 'effort' labelled.
Textbook References
- None
Website References
- None
Skills Addressed
Safety/Hazards
- A tank with water in it will be heavy and so is only to be moved by the technician; please refer to the Manual handling section of the Laboratory Lessons Health and Safety Risk Assessment
- When using springs goggles must be worn
- The main risk is from the vacuum pump and apparatus. The specific risk assessment must be read before using the apparatus.
- General Laboratory Health and Safety Risk Assessment
Notes
- None