Time dilation

Beeker

Something I always wondered.
Acording to Einstein the faster you travel the slower your clock. Also the closer you are to a mass the slower your clock.
Considering this I always wondered about Astronauts. In orbit they travel at 17500mph, so their clocks run slower {by a very tiny amount I know} compared to ones on the ground, but they are also further away from a mass {The Earth} so their clocks run quicker compared to the ones on the ground.
My question therefore is which has the greatest effect? The slowing caused by their speed or the quickening caused by distance from the Earth? Do they cancel each other out?

AlmightyCushion

In this exact scenario the lack of gravity creates a bigger effect meaning that time for them runs that little bit quicker. They've tested it using stupidly accurate clocks.

Capt'n Midnight

AlmightyCushion wrote: »

In this exact scenario the lack of gravity creates a bigger effect meaning that time for them runs that little bit quicker. They've tested it using stupidly accurate clocks.

GPS satellites orbit in 12 hours at an altitude of 20,200Km

https://secure.wikimedia.org/wikipedia/en/wiki/Error_analysis_for_the_Global_Positioning_System

When combining the time dilation and gravitational frequency shift, the discrepancy is about 38 microseconds per day,
...
To compensate for the discrepancy, the frequency standard on board each satellite is given a rate offset prior to launch, making it run slightly slower than the desired frequency on Earth; specifically, at 10.22999999543 MHz instead of 10.23 MHz.

So the effect isn't huge.

don't forget that while we are at the bottom of a gravity well we also experience movement and variable gravity. You weigh less at the equator due to the rotation, but you will also find time runs slightly faster (though pendulum clocks swing slower )

Beeker

Thank you for that:)

mawk

bang goes the theory actually ran this experiment this season. they had dallas hop on a string of planes and fly a full lap of the world with a caesium clock or something similar after syncing it with another one. the altitude and the speed both had an affect.

they ran the calculations beforehand and resulted pretty dame close to the actual dt.