1. Chapter 5
Work and Energy

2. 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

3. 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

4. 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