Idea 3of 6Builds onPaying with a pushWhich way
Only along the push
Carry a heavy box across a room. Work on it?
Today you'll discover
- what carrying sideways buys, strictly
- the part of a force that counts
- a push that takes energy away
Think firstA box carried across a room, level
You carry a heavy box across a room at a steady height. Work on the box?
Decide first, then press Next. Watch the force's shadow on the direction of motion.
A crate on a floor with a force arrow pointing straight up and a displacement arrow along the floor. After a prediction, the right angle between them is marked, then the force's shadow on the motion is shown as nothing. The force then tilts to sixty degrees and a shadow appears, with the work printed. The last step turns the force against the motion.
See the whole ideathe big idea and the key word, in one place
The big idea
Only the part of the force along the motion works.
Compare themLifting a box 1 m up: work, its height energy grows. Carrying it 10 m across: no work on it, strictly, though your arms disagree.
About this modelOnly the part of the force along the motion does work: W = F Δd cos θ.
Only the part of the force along the motion does work: W = F Δd cos θ.
Ready to use it?
- Say whether a described force does positive, negative or zero work, and why.