http://www.ck12.org Chapter 4. Motion and Forces
4.36 Work
- Define work.
- Relate work to force and distance.
The teens in the picture on the left are having fun playing basketball. The teen in the picture on the right is working
hard studying for an exam. It’s obvious who is doing work—or is it? Would it surprise you to learn that the teens
who are working are the ones who are having fun playing basketball, while the teen who is studying isn’t doing any
work at all? The reason why has to do with how work is defined in physics.
Defining Work
Work is defined differently in physics than in everyday language. In physics,workmeans the use of force to move
an object. The teens who are playing basketball in the picture above are using force to move their bodies and the
basketball, so they are doing work. The teen who is studying isn’t moving anything, so she isn’t doing work. Not all
force that is used to move an object does work. For work to be done, the force must be applied in the same direction
that the object moves. If a force is applied in a different direction than the object moves, no work is done. The
Figure4.70 illustrates this point.
FIGURE 4.70
Q: If the box the man is carrying is very heavy, does he do any work as he walks across the room with it?