Forces and Motion

Slow motion falling

Classroom Activity for 5-11 Supporting Physics Teaching

What the Activity is for

This is a compare and contrast activity. Compare the fall of the seeds that have evolved to fall slowly with those that have not. As we already have a description of motion for the slow falling seeds, you might reasonably expect the faster falling seeds to show the same pattern, even though our eyes are not up to the task (although a high-speed camera is).

What to Prepare

  • sycamore seeds
  • dandelion seeds
  • a dried pea or bean, as a seed that does not float
  • a frame for recording the speeds over the fall

What Happens During this Activity

Drop the dandelion seed, and summarise its motion over the four stages, drawing on the previous activity. We'd suggest here focusing on a description using arrows rather than words.

Drop the sycamore seed, and produce a summary of its motion. Its journey time is somewhat shorter, given that you have dropped it the same height, so the speeds will all be somewhat larger. You will need to develop the idea that the arrows will all be a bit longer through discussion, perhaps drawing on everyday journeys closer to home. the idea is essentially simple – that longer arrows lead to a shorter journey time: you cover more metres in each second.

Now might be the time to do a bit of predicting. Produce the bean seed and ask:

Teacher: We've got the patterns for the sycamore seeds and the dandelion seeds. What will the pattern look like for this been seed? In what ways will be different from the other two seeds?

You will need to run some discussion in order to develop the idea that the pattern is the same, but though there is some systematic variation across the seeds. Being able to line up all three completed frames will help you to establish the pattern, and to see the variation.

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