Why Does Light Move? Exploring Its Properties

[sophiecentaur]

Momentum, yes. But KE? How would you detect it?

 

[Subductionzon]

Is there a way to measure the kinetic energy of a photon using relativity? I know you could try to measure it with Newtonian mechanics but I am pretty sure that the answer would be wrong.

 

[Drakkith]

Is there a way to measure the kinetic energy of a photon using relativity? I know you could try to measure it with Newtonian mechanics but I am pretty sure that the answer would be wrong.

Not really. Per the definition from wiki:

The kinetic energy of an object is the energy which it possesses due to its motion.[1] It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. The same amount of work is done by the body in decelerating from its current speed to a state of rest.

A photon requires no energy to accelerate up to c, it simply moves at c always. Furthermore, a photon could never be decelerated either. In addition to that, a photon always moves at c regardless of who is observing it, which means that it's kinetic energy could not be based upon it's motion, as it moves at the same velocity in all frames yet it's energy differs.

 

[truesearch]

I have received an 'infraction' as a result of my posts following post *10.
Therefore, as much as I would like to contribute to this discussion I fel that I must keep quiet.

 

[Drakkith]

I have received an 'infraction' as a result of my posts following post *10.
Therefore, as much as I would like to contribute to this discussion I fel that I must keep quiet.

Well, as long as you don't do whatever the infraction was telling you not to do you should be fine!
And don't worry too much. An infraction is like a "notification" that just tells you that you've done something you maybe shouldn't have. It's not a warning and it doesn't count against your points on the forum. It's just there to let people know they've strayed a little too far from the main road before they get too far off and start to get warnings and such.

 

[truesearch]

what I did was to repeat what a 'science advisor' did... I quoted his/her quote.
I am interested in physics not other peoples quotes.
Say no more about it... let's concentrate on physics

 

[sophiecentaur]

Is there a way to measure the kinetic energy of a photon using relativity? I know you could try to measure it with Newtonian mechanics but I am pretty sure that the answer would be wrong.

You could 'infer' a value for KE, perhaps, but not measure it. In any case, the energy of a photon is just its energy and of an type that is specific to photons. Why should it be related to half m vsquared? (If it doesn't have a mass) People make the same mistake about the momentum of a photon and try to relate it to an mv definition.

 

[Leland]

My bad, momentum is a much better word.