Revision as of 05:02, 17 April 2009

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.

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

Using a large lever vary the distance to the pivot and use a forcemeter and pulley system 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.

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.

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 attempt activity 2 and one group will 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 try

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.

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

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 =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 from forcemeters, masses to hang, 1/2 meter rule
+* 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.