Forces and Motion

Increasing and constant speeds

Classroom Activity for 5-11 Supporting Physics Teaching

What the Activity is for

Same speed: changing speed. Here we revisit the walk-throughs of falling, with a careful emphasis on noticing the changing speed.

What to Prepare

  • a dandelion seed, or downy feather
  • a frame for recording the speeds over the fall

What Happens During this Activity

Drop the Seed or Feather, and ask for a careful description of how it moves. Focus on the vertical movement – just the falling.

As before, split the motion into several stages.

  1. just as the feather or seed is released
  2. just after the feather or seed is released
  3. a long time after the feather or seed is released
  4. a very long time after the feather or seed is released

In this case would suggest that you avoid including the collision of the feather of the ground.

The idea behind choosing a feather or seed is that it very clearly speeds up and then drifts down at a more or less constant speed for the remainder of the fall. You could verify this, at least approximately, by making regular marks on a whiteboard past which the feather or seed falls. For the majority of the journey these will be evenly spaced, showing a constant speed.

As a summary of the discussion about the motion of this object, we suggest producing a large frame, with written descriptions of the speed and arrows to show the speed at each of the four stages.

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