Work and EnergyWork and Energy

CCEA Physics page 9CCEA Physics page 9

Learning IntentionsLearning Intentions

By the end of the lesson we will be able By the end of the lesson we will be able to…to…

- Define the term Define the term ‘work done’‘work done’ using it using it correctly in the context of physicscorrectly in the context of physics

- Recall the Recall the equationequation for work done, for work done, including the unitsincluding the units

- Calculate work done in a number of Calculate work done in a number of simple experimentssimple experiments

I’VE BEEN WORKING ALL

FREAKIN’ DAY!!!

Some people work harder than others…

In Science the word ‘work’ has a very definite meaning…

Even Jack ‘I always stop the terrorists’ Bauer knows that energy and work are interrelated!!

By definitionBy definition

Work is defined as aWork is defined as a forceforce acting upon an acting upon an object to object to causecause a a displacementdisplacement

For example, a horse doing work by pulling a For example, a horse doing work by pulling a cart- the cart- the forceforce is provided by the horse and the is provided by the horse and the displacementdisplacement is the distance the cart moves is the distance the cart moves

Now your turn…Now your turn…

Draw on the Draw on the ForceForce and the and the DisplacementDisplacement for the three examples-for the three examples-

Is it an example of work?

Calculating WorkCalculating Work

The The equationequation for working out work (…see for working out work (…see what I did there?) is simply-what I did there?) is simply-

Work = Force x DisplacementWork = Force x Displacement

Wee note- The displacement needs to be in the same direction as the force

W W == FF xx dd

Word Equation

Dimensions

Units JoulesJoules == NewtonNewton xx metremetre

Using the equationUsing the equation

Example 1Example 1Take 1 kg weight = 10 newtonsTake 1 kg weight = 10 newtonsCalculate the work done when…Calculate the work done when…a)a) A mass of 5 kg is lifted 50 cm,A mass of 5 kg is lifted 50 cm,b)b) A mass of 300 g is lifted 150 cm.A mass of 300 g is lifted 150 cm.- a) Force = 5 x 10 = 50 Na) Force = 5 x 10 = 50 N- Distance = 0.5 mDistance = 0.5 m- Work Done = 50 x 0.5Work Done = 50 x 0.5

= 25 J = 25 J Try b) by yourselfTry b) by yourselfAns. Work Done = Ans. Work Done = 4. 5 J4. 5 J

Exercise 1Exercise 1

Complete the following questions by Complete the following questions by yourselfyourself

1.1. A lift of mass 250 kg carries a man of A lift of mass 250 kg carries a man of mass 76 kg. How much work is done by mass 76 kg. How much work is done by the wire rope which draws the lift through the wire rope which draws the lift through a height of 15 m?a height of 15 m?

2.2. A man walks up a hill of incline 30A man walks up a hill of incline 30º for º for 150 metres. If his weight is 750 N, how 150 metres. If his weight is 750 N, how much work has he done against gravity?much work has he done against gravity?

30

150150 sin 30 = 75 metres

48900 J or 48.9 kJ

56250 J or 56.25 kJ

The force in the equation is linked to the mass, how?

What is the total force in the question?

What is the ‘work done’ equation

Put the values of the force (in Newtons) and the distance (in metres) into the equation