# Does light ever accelerate?

• B

## Main Question or Discussion Point

I know that light is always at constant speed but does it ever accelerate when changing direction, if you put light through lots of different densities it curves into the Brachistochrone curve, would that be an instance of light acceleration.

• ISamson

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mfb
Mentor
I know that light is always at constant speed
In vacuum.
but does it ever accelerate when changing direction, if you put light through lots of different densities it curves into the Brachistochrone curve, would that be an instance of light acceleration.
I guess you can call that acceleration, yes.

You can get a speed that changes continuously if you send it through a variable medium, e.g. through the atmosphere vertically (as the speed of light at sea level pressure is lower than the speed of light higher up).

Dale
Mentor
I know that light is always at constant speed but does it ever accelerate when changing direction, if you put light through lots of different densities it curves into the Brachistochrone curve, would that be an instance of light acceleration.
In a rotating reference frame light does accelerate in a vacuum

Orodruin
Staff Emeritus
Homework Helper
Gold Member
In a rotating reference frame light does accelerate in a vacuum
Coordinate acceleration ... You might as well say it does not have constant speed.

• Dale
Dale
Mentor
Coordinate acceleration ... You might as well say it does not have constant speed.
Yes

CWatters
Homework Helper
Gold Member
I know that light is always at constant speed but does it ever accelerate when changing direction, if you put light through lots of different densities it curves into the Brachistochrone curve, would that be an instance of light acceleration.
I recall someone posted a homework question that went something like...

A beam of light is bent by a prism mounted on sensitive weighing scales. Calculate the apparent change in weight when the light is turned on/off.

sophiecentaur