Science Form 3 Topic 7.1 Work, Energy and Power

Chapter 7
Energy & Power

Topic 7.1

Work, Energy & Power

Learning standard:
7.1.1 Define work and solve problems related to energy in the context

of daily life.

Work, W = the product of force, F, and
the displacement, s,
in the direction of the force, that is W = Fs

S.I. Unit for WORK : Joule (J)
[ 1 joule (J) of work done is when
a force of 1 newton (N) is used to move an object
over a distance of 1 metre (m) in the direction of the force,
that is 1 J = 1 Nm; 1 J = 1N x 1m ]

Work, W = Force (F) x Distance (s)
W=Fxs

Note:

*Direction can be: HORIZONTAL or VERTICAL
• 1000 Joule (J) = 1 kilojoule (kJ)
• 1 kg = 10 N





Is work done?

Is work done?









Topic 7.1

Work, Energy & Power

Learning standard:
7.1.2 Relate power with work and solve problems in the context of
daily life.

Energy and Power

ENERGY = the ability to do work
S.I. unit for energy : Joule (J)
[ 1 joule (J) of work done is when
a force of 1 newton (N) is used to move an object
over a distance of 1 metre (m) in the direction of the force,
that is 1 J = 1 Nm ]

Energy and Power

POWER = RATE of doing work

S.I. unit : watt (W)
[ 1 watt (W) of power used is
1 joule (J) of work is done in 1 second (s)]

Power, P = ,
,

P =




How work and power relates:







When doing a chin-up, a physics student lifts her 40 kg body
at a distance of 0.25 metres in 2 seconds. What is the power
delivered by the student’s biceps?

Step 1: Calculate the WORK done

W=Fxs

= (40 x 10)N x 0.25 m

= 400 N x 0.25 m

= 100 J

Step 2: Calculate POWER

P =


= 100
2

= 50 W