• Question: why does stuff nearer you look like it's going faster?

    Asked by Kate and Peckasso :) to Chris, Josh, Rebecca, Rob, Susan on 22 Jun 2015.
    • Photo: Chris Armstrong

      Chris Armstrong answered on 22 Jun 2015:

      All based on perception, and frame of reference.

      If something is moving fast very close to us, its able to enter and leave our vision very quickly. But further away an object at the same speed has to travel a far greater distance in order to achieve the same result.

    • Photo: Susan Cartwright

      Susan Cartwright answered on 23 Jun 2015:

      Think about triangles.

      Suppose you are standing on a bridge over a motorway. About 10 m below you, cars are rushing by at 31 m/s (about 70 mph). This means that if we draw a triangle with its corners at you, the car at time t, and the car at time t+1 s, assuming that at t+0.5 s it was directly underneath you, then the angle of that triangle at your corner is about 114 degrees. This is a big angle – the car’s position is changing very quickly.

      Now you look up, and see an aeroplane. The plane is doing 240 m/s (about 535 mph, fairly typical of a commercial jet), but it is 10000 m up (again, fairly typical for a commercial jet). The triangle you make this time has an angle at you of only 1.4 degrees: even though the plane is actually moving much faster than the car, it does not move nearly as quickly across your field of view.

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