3.2 Work

Natural sciences

Grade 9

Energy, forces and machines

Module 20

Work

Activity:

Calculating work/effort (performance)

[lo 2.3; lo 2.4]

We have established that objects can be moved around by applying FORCES. The application of force means that WORK is performed. WORK is the scientific term used to refer to this application of force.

We say that 1 Joule of work is required to move the force of 1 Newton over a distance of 1 metre!

• Remember that effort actually indicates the use of energy. A Joule therefore indicates the amount of energy that is required to move 1N over a distance of 1 metre.

Questions:

1. How much effort do you apply when you:

a) drag a 10-N brick over a distance of 3 metres?

b) drag a brick with a mass of 2,5 kg over a distance of 5 m?

2. The energy value of a bar of chocolate is 300 kJ. How many 2,5-kg bricks will you be able to drag for a distance of 5 metres with this amount of energy?

3. How far will the energy provided by another bar of chocolate enable you to drag one such brick?

You have made use of the formula :

W = F × s

W : Work F : Force s : Distance

• WFsThe placement of the letters in the triangle will help you to remember how to use the formula. Your educator will explain this to you.

• Now calculate how much energy will be required to move yourself over a distance of 10 metres.

Your educator will provide you with further exercises dealing with movement/acceleration.

Assessment of CALCULATION OF ENERGY USAGE (EFFORT)

[LO 2.3; LO 2.4]

Assessment

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:

• interprets information;

2.4 applies knowledge.

Memorandum

Work/effort

Activity

Questions:

1. a) F × s = 10N × 3m = 30 Joule

b) F × s = (2,5 × 10) × 5 = 125J

2. 300 kJ = 300 000J divided by 125J = 2 400 bricks

3. 300 000J divided by 25N = 12 000 m = 12 km

• Energy required to move a learner over a distance of 10 m:

Learner's mass = A

W (energy) = F (force) × s (distance) = (A X 10) × 10m