Chapter 13.1 – Work, Power, and Machines

work –

transfer of energy to an object by the application of a force that causes the object to move in the direction of the force

- found by multiplying the force by the distance over which the force is applied

Work = force x distance

W = F d

- units of joules (J)

- if an object does not move, no work is done, work = zero

Chapter 13.1 – Work, Power, and Machines

An apple weighing 1 N falls a distance of 1 m. How much work is done on the apple by the force of gravity?

A bicycle’s brakes apply 125 N of frictional force to the wheels as the bike moves 14.0 m. How much work do the brakes do?

Chapter 13.1 – Work, Power, and Machines

power –

rate at which work is one or energy is transformed

Power =

P =

- unit of power is watt (W)

Chapter 13.1 – Work, Power, and Machines

While rowing across a lake, John does 4000 J of work on the oars in 60.0 s. What is his power output?

Anna walks up the stairs on her way to class. She weighs 560 N and the stairs go up 3.25 m vertically. If Anna climbs the stairs in 12.6 s what is her power output?

Chapter 13.1 – Work, Power, and Machines

- machines help do work by changing the size of an input force, the direction of the force, or both

- they multiply the force

mechanical advantage (MA) –

how much a machine multiplies force or distance, ratio between the input force and output force, or ratio between input distance

and output distance

mechanical advantage =

- less force over a greater distance, same work

Chapter 13.1 – Work, Power, and Machines

What is the mechanical advantage of a ramp that is 6.0 m long and 1.5 m tall?

Alex pulls on the handle of a claw hammer with a force of 15 N. If the hammer has a mechanical advantage of 5, how much force is exerted on the nail in the claw?