1. PHYSICISTS ASSEMBLE!!!!

this is a thread about all things physics.

Firstly this is a problem that has bothered me for a while but I cant seem to get a valid answer from anyone I ask.

Light moves in a straight line and at a constant speed except when it enters a medium which it then slows down (I believe most of us can agree on this),
now my question is how is it possible for it to revert back to its original entrance speed when exiting the medium with no external force or energy applied the light beam. this makes no sense to me, first I am taught a body will remain stationary or in the same velocity unless an external force is applied to it ( Newton's first law ) now they teach me this and expect me to point blank accept this. Now I bid you physicist of the internet to prove to me that this makes any sense.

2. I think you should create accounts here and here.

Asking people about physics here is akin to asking a smart and well read librarian about some random topic when instead you could just go ask experts. The brain power of many vs the brain power of few. Will they be INTPs? *shrugs*

3. It sounds like the answer would be in this thread but I'm not sure which post says it best.

4. Originally Posted by BarIII
It sounds like the answer would be in this thread but I'm not sure which post says it best.
Thanks a lot for the link but my question still goes answer, what I got from that thread was that Newton's laws are not perfect and to accept this phenomenon as it is.

5. After looking through the first page of these results I'm inclined to disregard Newton.

This thread may help.

Your question was asked here by ProbingOmega:

"...the photons resumed the speed of light +/- after exiting the medium...What is the engine that converts and directs energy into motion and direction for the photon?"

Maybe the reply by Adam Lilien will help.

6. Originally Posted by KingTurk
this is a thread about all things physics.

Firstly this is a problem that has bothered me for a while but I cant seem to get a valid answer from anyone I ask.

Light moves in a straight line and at a constant speed except when it enters a medium which it then slows down (I believe most of us can agree on this),
now my question is how is it possible for it to revert back to its original entrance speed when exiting the medium with no external force or energy applied the light beam. this makes no sense to me, first I am taught a body will remain stationary or in the same velocity unless an external force is applied to it ( Newton's first law ) now they teach me this and expect me to point blank accept this. Now I bid you physicist of the internet to prove to me that this makes any sense.
Light is not a body so Newton's laws of motion don't apply to it. Maxwell's equations describe the behaviour of electromagnetism.

Light is an electromagnetic wave. A time-varying electric field gives rise to a time-varying magnetic field, which gives rise to a time-varying electric field and so on. This is the way light propagates. Electric and magnetic fields travel outwards from the point where they are created but they have a speed of propagation. They don't fill space instantaneously. The speed of a light wave in a particular medium is really a function of the speed of the propagation of electric and magnetic fields in that material. A vacuum has the least resistance to the propagation of electric and magnetic fields but, even in a vacuum, electric and magnetic fields don't propagate instantaneously.

If you turned on an electromagnet to pick up a paperclip, there would be a very very very short delay (magnetic fields propagate very quickly) before the magnetic field reached the paperclip.

Light waves are just electric and magnetic fields spreading sequentially outwards. The speed at which this happens depends on the material. No extra energy has to be given to the wave to make it speed up.

To make an analogy, imagine a relay race that starts on concrete, moves to sand then finishes again on concrete. The runners will slow down when on the sand because they can't move as quickly on sand as they can on concrete but will speed up again when the move back to concrete. Each runner just runs his fastest for whatever material he is running on.

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