Next: Kinetic Energy and the Up: Work and Energy Previous: Work and Energy

# Work

Definition: The work done by an agent exerting a constant force ( ) and causing a displacement ( ) equals the magnitude of the displacement, s, times the component of along the direction of . In Figure 5.1, the work done by is:
 W = s Fcos .

Note:

• If = 0 W = 0. (ie: no work is done when holding a heavy box, or pushing against a wall).
• W = 0 if (ie: no work is done by carrying a bucket of water horizontally).
• The sign of W depends on the direction of relative to : W > 0 when component of along is in the same direction as , and W < 0 when it is in the opposite direction. This sign is given automatically if we write as the angle between and and write W = Fscos .
• If acts along the direction of then W = Fs , since cos = cos 0 = 1.
• Work is a scalar.
• The SI units of work are Joules (J) (1 Joule = 1 Newton meter). In cgs units: 1 erg = 1 dyne cm.

Next: Kinetic Energy and the Up: Work and Energy Previous: Work and Energy