Work, Power and Energy

When a force moves an object, energy is transferred and work is done.

Work done is the amount of energy transferred when a force is applied to an object to make it move.

Although work and energy are both measured in Joules (J), work done is not a type of energy - it's a type of energy transfer.

Work done is calculated by multiplying the force (F) that's applied to an object by the distance (s) that the object moves in the direction of the force.

WORK DONE = FORCE X DISTANCE

Power is the rate at which work is done -- it's the work done per second. It's measured in Watts. One watt means one joule of energy is transferred per second.

Work done is the energy transferred, therefore:

POWER = WORK DONE / TIME TAKEN

or:

POWER = (FORCE X DISTANCE) / TIME TAKEN

Have a go at these:

1) Sara is stacking bookshelves. Each book weighs 2N and she puts them on the top shelf, 2m above the floor. How much work does Sara do by putting one book on the top shelf?

2) Sara puts 35 books individually from the floor onto the bookshelf. It takes her 12 minutes. What is her power?

3) A body builder lifts a weight of 1500N a distance of 0.5m. What is the work done in lifting it 5 times?

(answers on the next card)

1) 2N x 2m = 4 J

2) 4 x 35 = 140
140 / 12 = 11.7

3) 1500 x 0.5 = 750 J
750 x 5 = 3750 J