Chapter 5: Work, Power, and Energy

Chapter 5-1 (p. 168-171)

Physics

There are two types of work

1. Everyday sense

“I work at McDonald’s.”

“It is hard work to think this much.”

There are two types of work.2. Scientific sense

Work – a force that causes a change in motion (force across a distance)

Example – pushing a car or riding a bike

Calculating Work

- Work = force applied across a distance

W = F•d•(cos θ)

W = work measured in Joules

F = force measured in Newtons

d = displacement measured in meters

θ = angle between force and displacement

- if θ = 0 then cos θ = 1

- if θ = 90 then cos θ = 0

Units of work- Work is measured in Joules (J)

1 Joule = 1 Newton x 1 meter

1 J = work of lifting an apple from your

waist to the top of your head

- The SI units for work are named for James Prescott Joule (1818-1889), a British physicist who did much research in the area of energy

Positive or Negative Work

- Since work is dependent on displacement, and displacement is directional, therefore work is directional.

Positive or Negative Work

• Work can be a positive or negative depending on the direction of applied force in relation to displacement of the object.