Idea 1of 6Builds onThe net arrow
Nothing needs a push to keep going
The push stops. What keeps the crate sliding?
Today you'll discover
- what keeps a crate sliding after the push stops
- the only sideways arrow, and which way it points
- why motion needs no maintainer
Think firstThe hand lets go. The crate keeps sliding
The push has stopped, but the crate still slides. What keeps it going?
Decide first, then press Next. Look for an arrow that points the way the crate moves.
A box on a floor marked as moving to the right, with a dot at its centre. After a prediction, arrows appear: Earth's pull down, the floor's push up, and a drag to the left; no arrow points right. A heavier net arrow then appears beside the box pointing left. The last step asks what a puck on frictionless ice does.
See the whole ideathe big idea and the key word, in one place
The big idea
With no net force, an object keeps its velocity.
Easy to get wrongA push cannot be stored in an object and used up later. Once the hand lets go, there is no forward force. What you feel as 'the push wearing off' is the drag doing its job.
Key word
- first law
- Newton's first law: with zero net force, velocity stays constant, rest included
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?
- Explain what keeps a described object moving, and what slows it, using only real forces.