3.6 Levers

Natural sciences

Grade 9

Energy, forces and machines

Module 24

Levers

Activity:

Identifying levers as mechanisms to identify energy transfer

[lo 2.2; lo 2.3; lo 2.4]

The operation of the simple appliances given above depends on the principle of the lever.

• All levers have a PIVOTAL POINT or FULCRUM , a point where effort or power is applied (or the POWER POINT) , and an AREA OF LOAD called LOAD (L) .
• The relevant symbols are:

• P = point/fulcrum
• E = effort/power
• L = load

• Levers are classified according to the position of the fulcrum.
• There are three classes of levers.

• Class 1 lever
• Class 2 lever
• Class 3 lever

CLASS 1: Fulcrum in the middle

e.g. a see-saw

CLASS 2 : Load in the middle

e.g. a wheelbarrow being pushed

CLASS 3: Effort/Power in the middle

e.g. a golf club or broom held for use

Identify the class of lever in each of the following examples:

a) You pick up a can of cold drink and raise it to your mouth.

b) You stand on the tips of your toes.

c) You hold a fishing rod, having hooked a large fish.

d) You row a boat using an oar.

Assessment of classification of LEVERS

Were you able to place the examples in categories?

[LO 2.2; LO 2.3]

Activity:

Calculating mechanical advantage

[lo 2.4]

Force × distance = load × distance

• It is possible to calculate the mechanical advantage of a lever: the ratio of load to force provides this index.
• We refer to this as mechanical advantage.

1. How would one be able to enhance the mechanical advantage of a class 1 lever?

1. You have a nutcracker with the following dimensions:

• You require 150 N to crack the nut.

a) Which FORCE is needed?

b) What is the mechanical advantage of the nutcracker?

[LO 2.4]

The Wheel

Activity:

Researching the invention of the wheel and evaluating as an example of human endeavour

[lo 1.1; lo 1.2; lo 2.1]

The invention of the wheel more than five thousand years ago resulted in a remarkable change in human performance of work.

The wheel is like a lever, except that the movement comprises rotation around an axle and not an up and down movement around a fulcrum.

Project dealing with the WHEEL

Work as a group and create a poster to represent the development of the wheel and to illustrate different ways of using wheels.

• Did the Egyptians have wheels to assist them when they were building the pyramids?
• How did they manage to perform all these tasks?

Assessment of RESEARCH on the WHEEL

Were you able to plan and execute the investigation and to evaluate it?Were you able to gain INSIGHT into the VALUE of human scientific endeavour?

[LO 1.1; LO 1.3; LO 3.1]

Assessment

LO 1: Scientific investigations:

The learner will be able to act confidently on curiosity about natural phenomena, and to investigate relationships and solve problems in scientific, technological and environmental contexts.

This is evident when the learner:

• plans investigations;
• conducts investigations and collects data;
• evaluates data and communicates findings.

LO 2: Constructing Science Knowledge:

The learner will know and be able to interpret and apply scientific, technological and environmental knowledge.

This is evident when the learner:

• recalls meaningful information;
• categorises information;
• interprets information;

2.4 applies knowledge.

LO 3: Science, Society and the Environment

The learner will be able to demonstrate an understanding of the interrelationships between science and technology, society and the environment.

This is evident when the learner:

3.1 is able to show an appreciation of science as a human endeavour.

Memorandum

Activity

a) Class 3

b) Class 2

c) Class 3

d) Class 1

Activity

L.W. A study of levers is no longer required as part of the syllabus, but levers are referred to in this module to illustrate the transfer of energy from one body to another.

1. Reduce the force distance

2. a)

b)

Activity

Assess according to the learning outcomes and assessment standards indicated in the module.