The physics behind unraveling the mystery of what happened to Malaysian Airlines flight MH370 is all around us. We hear it when an ambulance whizzes past, and we see it watching a swan paddle across a lake. It's called the Doppler effect after nineteenth century Austrian physicist Christian Doppler who came up with it in 1842.

The Doppler effect describes how a wave changes frequency relative to the position of an observer. A good example is how the sound of a siren seems to change as an ambulance passes by. When an ambulance is moving towards you with its siren blaring, it takes slightly less time for each successive sound wave to reach you than the previous wave. In this way, it's not the pitch of the siren that changes but how you hear it.

Applying the Doppler effect

British satellite communications company Inmarsat was able to monitor pings transmitted every hour automatically by MH370. By factoring the angle of elevation and the time the pings took to reach the satellite, Inmarsat established two arcs that the aircraft could have taken: one in the north, and the other in the south. This data was then applied to the Doppler Effect.

"We then took the data we had from the aircraft and plotted it against the two tracks, and it came out as following the southern track," said Jonathan Sinnatt, head of corporate communications at Inmarsat.