Force
Forces and Motion

Bubbles

Classroom Activity for 5-11 Supporting Physics Teaching

What the Activity is for

Rising – the same physics as falling?

Here you are going to extend the description of motion that you have evolved for falling to things that rise. SO this is something of a reinforcement activity, showing how the ideas can be reused in a describing a new process.

What to Prepare

  • some cooling oil in a clear tall container
  • a means of introducing bottles to the bottom of the cooking oil
  • a Cartesian diver
  • small stones, that fall through the oil
  • a frame for recording the speeds over the fall or rise

What Happens During this Activity

Start by dropping the stones in the oil. Revisit the falling frames to record the changes in speed as the stone falls, again over the four stages:

  1. just as the stone is released
  2. just after the stone is released
  3. a long time after the stone is released
  4. just before the stone reaches the bottom

Make bubbles, and then ask for suggestions for completing the frames for the bubbles. We suggest the following four phases of such frames, as then the pattern will be directly comparable with the falling stones:

  1. just as the bubble is released
  2. just after the bubble is released
  3. a long time after the bubble is released
  4. just before the bubble reaches the top

Now complete the frames and compare the patterns. You should be able to flip one pattern to get another. The movement of rising bubbles are just the opposite of falling stones.

We'd suggest leaving the reason why this is the case as open at the moment – interesting, but not worth pursuing at the moment.

As an extension, you might consider using the Cartesian diver, which allows both rising and falling, and can therefore show both motions. You should avoid the temptation to explain how the Cartesian diver works – here it just provides a convenient process to study.

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