Chapter 5Work and Energy

Work• Equal to the magnitude of the force

times the magnitude of the displacement (W = Fd)

• Done only when the components of a force are parallel to the displacement (Figure 5-2)

• Work is not done unless the object is moved

Net Work• Net work = net force x displacement x

cosine of angle between them–Cosine 0 degrees = 1–Cosine 90 degrees = 0

• Units are force times length (N x M), or joules

• Three push-ups require about 1000 J

Work (cont.)

• Scalar • Can be positive or negative (figure 5-3)–Dependent upon force exerted

• If net work is positive, the object speeds up

• If net work is negative, the object slows down