Idea 2of 7Builds onThe drag against the slideThe touching test
The squeeze sets the price
Slide the crate twice as fast. More drag?
Today you'll discover
- whether sliding faster makes the drag bigger
- what the drag does depend on
- the number that rates two surfaces
Think firstSlide the crate twice as fast
The same crate slides twice as fast across the same floor. The drag?
Predict first, then drag the sliders. Watch what the drag does when the mass changes.
A box on a floor with four force arrows from its centre, the leftward drag highlighted. After a prediction the upward normal arrow is labelled, then the friction bench opens with sliders for mass and coefficient and readouts for the normal force and the friction. The last step moves the same crate onto ice.
See the whole ideathe big idea and the key word, in one place
The big idea
Friction is a fixed share of how hard the surfaces press.
Easy to get wrongFaster sliding does not drag harder. Friction depends on the normal force and the pair of surfaces. The identical readings at two speeds are not a coincidence.
Key word
- coefficient of friction
- μ, a number with no units that rates a pair of surfaces: Ff = μ FN
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?
- Price the friction on a described crate from its mass and the coefficient.