Chapter 12

Work, Power, & Machines

I. What is work?

A. Work – when force causes a change in an objects position.

1. Change must be in the direction force is applied.

Does this guy do work?

Yes b/c the car changed position

II. Measuring WorkA. The unit for work is the Joule (J).

A Joule is equal to lifting an apple 1 meter (about 3 feet off the ground.

An apple weighs about 4 ounces

Work = Force x Distance

Joules (J) = Newtons (N) x Meters (m)

Problem:An apple weighing 1 Newton falls a distance of 1 meter. How much work is done by the force of gravity?

GIVEN:F = 1 Nd = 1 mW = ?

WORK:W = F x dW = (1 N)(1 m)W = 1 J

F

W

d

Problem:While rowing in a race, John uses his arms to exert a force of 165 N per stroke while pulling the oar 0.8 m. How much work does he do in one stroke?

GIVEN:F = 165 Nd = 0.8 mW = ?

WORK:W = F x dW = (165 N)(0.8 m)W = 132 J

F

W

d

Assignment:

Make your paper look like this:

Work, Power, & MachinesABCDEFGH

Z