Levers

All teachers may not wish to use all the ideas suggested. It is up to you to fit them to your own pupils' needs and the school facilities.

Forces

Remind pupils what a force can do.
Effect of forces on materials - stretching, squashing, changing speed and twisting.

Levers

Introduce the idea of the turning effect of a force. Discuss, and/or demonstrate some of the following

Opening a door.
Tightening a nut with your fingers or with a spanner
Nut crackers
Crowbar
Using a screwdriver to open a tin of paint
Try lifting a weight with your arm bent and then outstretched
Arm wrestling
Carry objects of different weight on a tray and then remove one! (Problems for waiters)
Try cutting a piece of thin paper and then a piece of thick card using only the points of a pair of scissors.

See: Levers
See: Levers types

Demonstration 'experiment'

Simple turning forces – find the force needed to open a door. A good demonstration is to get one of the smaller pupils in the class to push on the edge of the door with one finger while you push on the other side with your hand right up close to the hinge – they will be able to 'close the door in your face'.
See: Creative teaching ideas/Lever

Follow up work and homework ideas:
Where are levers important in everyday lives?
The lever in the human body
Levers in sport especially athletics – pole vault, javelin

Class experiment

Get the pupils to investigate this themselves.
Then use a demonstration beam to confirm the ideas. I have found that a piece of wood at least a metre long suspended by string from the middle works well. Sets of slotted masses on string loops can then be moved along it. The good thing about this arrangement is that it keeps the centre of gravity of the system below the pivot point (necessary for stable equilibrium).
See: 11- 14/Statics/Experiments/Moments

Resources needed (per group):
2 sets of slotted masses (0 - 1kg) Metre ruler Plasticene (for fine adjustment) String

Simple moments and the lever law

From the pupils' results and also from a possible additional demonstration of the experiment introduce the idea of the moment of a force and deduce the 'lever law'.

Define a 'moment' as force x perpendicular distance from the pivot point
See: Levers

Make a child's mobile!

A very useful practical exercise on the application the lever law. Suggest up to three 'levels' within the mobile. Children could prepare their own shapes – say animals and balance the mobile by trial and error. Alternatively a set of pre-prepared shapes of known mass could be used. A really good group might be able to calculate the required position of each new shape on the mobile – tricky!

See: 11-14/ Mechanics/Statics/Problems/Levers 1
See: 11-14/ Mechanics/Statics/Problems/Lever law

Homework suggestions:
1. Make a list of where levers are used in your home
2. Set of problems on the lever

Types of levers.

Identify the different types of lever.
First order lever – pivot between load and effort – crowbar, claw hammer, pliers
Second order lever – load between pivot and effort – wheelbarrow, bottle opener, oar
Third order lever – effort between pivot and load – tweezers, forearm, fishing rod, safety valve