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Author Topic: If I run at 10km per hour inside a plane traveling at 800km an hour what speed am I moving at?  (Read 2070 times)

Offline thedoc

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Chris Grieshaber asked the Naked Scientists:
If I run at 10km per hour inside a plane traveling at 800km an hour what speed am I moving at?

What do you think?
« Last Edit: 06/01/2015 19:30:01 by _system »


Offline evan_au

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In Physics, you always need to measure speed relative to some "Frame of Reference".

There is no "Perfect" frame of reference, so all of the following answers are equally correct:
  • as seen by someone standing on the ground, you are traveling at 810 kph across the sky.
  • as seen by to someone sitting on the plane, you are traveling at 10 kph down the aisle.
  • as seen by the mobile phone in your pocket, you are effectively stationary.
  • as seen by someone standing on Pluto, you are traveling at 100000 kph around the Sun.

The idea that there is no "right" answer was a bit of a shock to some people when Einstein introduced his theory of relativity.

Offline Bill S

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Of course, one should use the relativistic velocity addition formula to answer your question, but at the low speeds (compared to the speed of light) you mention, the difference would be negligible.

Offline CliffordK

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Can I just say that 800 kph has one significant figure....  (although it is one of those ambiguous numbers).

So, you're still traveling 800 kph  :)

Offline jeffreyH

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It all depends upon the forces acting on the plane. In a severely time dilated field both the runner and the plane would appear to be traveling faster than would be apparent to a distant observer. Simply because while the object has a specific velocity as viewed remotely time for the passengers has slowed so the relationship between perceived distance traveled over time taken has changed.

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