Idea 3of 7Builds onThe squeeze sets the price
It holds, then it slides
A gentle push; the box stays put. Any drag?
Today you'll discover
- whether a box that has not moved is being dragged
- what happens the moment it breaks loose
- two names for one drag, before and during
Think firstYou push a heavy box gently. It does not move
You push gently and the box stays put. Is there a drag on it?
Decide first, then press Next. Watch the drag arrow grow, then settle.
A box on a floor with a dot at its centre and a small push arrow to the right. After a prediction, a drag arrow to the left appears and grows with the push, then settles at a slightly smaller steady length once the box is marked as sliding. The two drags are named. The last step removes the push mid-slide and asks what the drag does.
See the whole ideathe big idea and the key word, in one place
The big idea
Static friction holds to a limit; kinetic friction drags steadily.
Compare themStatic: matches the push, any size up to its limit, no sliding. Kinetic: one steady size, against the slide. The static limit is usually the bigger of the two.
Key words
- static friction
- the friction that stops two surfaces starting to slide; it matches the applied force up to a maximum, Ff ≤ μs FN
- kinetic friction
- the friction while surfaces slide: a steady Ff = μk FN, usually smaller than the static maximum
About this modelArrows are forces, not motion: a box can move with no arrow pointing its way.
Arrows are forces, not motion: a box can move with no arrow pointing its way.
Ready to use it?
- Say which friction acts on a described object, and what it matches or equals.