Physics · Rung 6 of 23

Motion

Three ways of moving and how to tell them apart without a stopwatch: at constant speed you cover the same distance every second; accelerating, more each second than the last; braking, less. Falling is the case that surprises people most, because a feather and a hammer fall the same when there is no air — and it is not a thought experiment: Dave Scott did it on the Moon in 1971 and it is on film. Here you predict where something will be, you do not calculate when.

Where this sits

Comes after
The graph
Opens up
The experiment, Acceleration

Exercises from this rung

Generated by the app, from easiest to hardest

  1. a raindrop halfway down

    • It moves at a constant speed
    • It is accelerating
    • It is slowing down
    • It is completely still

    Why It stops accelerating almost at once: the air resists as much as it weighs, and it falls at about 9 m/s.

    easier

  2. a suitcase on an airport belt

    • It moves at a constant speed
    • It is accelerating
    • It is slowing down
    • It is completely still

    Why It moves at the belt's speed, no more and no less, with nothing pushing it forward.

    in between

  3. a feather and a hammer dropped on the Moon

    • It is accelerating
    • It is slowing down
    • It moves at a constant speed
    • It is completely still

    Why They land together. With no air, mass does not change the fall: Dave Scott filmed it in 1971.

    harder