Work
The energy a force transfers when it moves something. Work is force times distance moved along the force, W = F d cos theta.
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Analogy
Pushing a car: no movement, no work, however tired you feel.
Example
W = F d cos 60W = 50 x 10 x 0.5W = 250 J
In practice
A 50 N pull at 60 degrees over 10 m does 250 J of work.
Practice
Flashcards
- What is one joule?The work done by a 1 N force over 1 m, equal to 1 kg m^2/s^2.
Questions people ask
Can a force do zero work?
Yes. If the object does not move, or if the force is at right angles to the motion, no work is done. A waiter carrying a tray at constant height does no work on the tray with the upward support force, because it is perpendicular to the motion.
Can work be negative?
Yes. When a force points against the motion, it takes energy away from the object. Friction on a sliding box does negative work, which slows the box, and that work equals minus F times d. Negative work reduces kinetic energy, while positive work increases it.