Measuring Energy Part 1Newtons, Joules, Watts

Energy Use in Canada• Canadian households used 1,425 petajoules of

energy in 2011 (StatsCan)• 1 petajoule is approximately the amount of

energy needed to run the TTC subway for one year

Newton (N)• SI unit of FORCE– Force is a push or pull against an object

• 1 Newton is the amount of force needed to accelerate a mass of 1 kg by 1 meter/s2

N = kg x m/s2

A newton will move 1 kg of weight• one meter in the first second, • 2m in the second second• 3m in the third second

Newton (N)

Time 1 Second 2 Seconds 3 Seconds

1 KG

1 KG 1 KG

1 KG1 KG

1 KG

Joule (J)• SI unit of energy and work – Energy is the ability to do work– Work is the energy transferred when a force moves an object

• 1 joule is the work done/energy transferred when 1 newton of force moves an object 1m.

J = N x m (N=newton, m=meter)

One joule equals the energy needed to lift an apple from the floor to the tabletop, about 1m.

Watt (W)

• The SI unit of power– Power is the rate at which work is done

• One watt is equal to 1 joule of energy produced per second

W = J/s(j=joule, s=sec)

Watt hours (Wh)• Light bulbs are rated according to the power they

use• this is measured in Watt hours (Wh).

Since there are 3600 (60 x 60) seconds in an hour

one watt hour = 3 600 joules of energy

• A 20 watt lightbulb uses 20 watts of power in an hour. – A 20 watt bulb uses 3 600 X 20 = 72 000 joules of energy

Kilowatts (KW)

• 1000 Watts is a kilowatt (KW)

• A kilowatt hour (KWh) is equal to 1000 watt hours (Wh)

One KWh = 1000 watt hours

1000 watt hours = 1000 x 3 600 = 3 600 000 joules