Forces and Motion

Relative motion and PoV

Classroom Activity for 14-16 Supporting Physics Teaching

What the Activity is for

Here students get to see a process from a second point of view, moving with respect to the first, and so get practice in putting themselves in another's shoes.

The ability to see the situation from several different points of view is essential to developing fluency in describing motion. It's also a very useful precursor to the approach developed in the Physics Narrative of episode 04, although we suggest that you avoid colliding the vehicles here, so avoiding an interaction.

What to Prepare

  • two small video cameras
  • two freely running vehicles
  • a screen to display clips, preferably side by side

What Happens During this Activity

We suggest restarting the relative motions to one line, rather than a plane, or higher dimensions: so run the vehicles either parallel or anti-parallel to one another. In either case there should be relative motion between the two. Mount one video camera on each vehicle pointing at right angles to the motion, so that it will see the other vehicle pass. Pay attention to the backgrounds of both cameras, so that there is something significant to be seen as they scan past. We suggest using a clap or other percussive noise to be captured by the running video cameras, as a means of synchronising the two recordings.

Before showing the clips it's worth asking the students to agree on what the clips will show, expecting them to translate from their point of view.

You might even exploit the Alice, Bob and Charlie routine in the Physics Narrative to discuss the three different points of view.

The experiment might be followed up by other clips from the moving object (there are many posted on the internet, or students may have some, as a result of the spread of sports-cams), and ask the students to describe the motion from a different point of view (note: a description does not have to be restricted to words).

appears in the relation F=ma a=dv/dt a=-(w^2)x
is used in analyses relating to Terminal Velocity
can be represented by Motion Graphs
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