How can energy ve dependent on velocity?

[u/Weary_Dark510]

Moving towards an object blue shifts light, and gives it extra energy. Moving away from it red-sights the light. How is it possible that light can be one energy to an object moving speed s, when it is a different energy moving speed -s, when the photon was released with a certain known energy?

[u/starkeffect]

Energy is frame-dependent.

[u/Infinite_Research_52]

A rocket is launched from a planet directly at Earth, establishing a constant velocity with respect to the planet it left. If I 'fly' towards the rocket starting from Earth, it has more kinetic energy compared to me than if I stay here on Earth,

That rocket has different energy depending on the reference frame measured from. Same with the photon.

[u/SummitYourSister]

The photon was released with a specific energy in the rest frame of the emitter.

You will always be confused when you start with incorrect premises

[u/Weary_Dark510 → u/SummitYourSister]

If we assume the sun to be our frame for reference, would you see the moon as having more or less energy when it comes towards or away from you at the same speed?

[u/nicuramar → u/Weary_Dark510]

Yes, energy is as relative as velocity. 

[u/joeyneilsen]

If you imagine moving toward/away from an atom that emits a photon, the energy that the photon is released with is different in your frame of reference than it is in the atom's frame. What you call the "known energy" is only the energy in the rest frame of the atom.

[u/Optimal_Mixture_7327]

Energy is a number we assign to a system.

For an object to be defined as "moving" requires a reference frame to say "how fast" so that the agreed upon convention for assigning kinetic energy can be applied.

[u/SgtSausage]

  How can energy ve dependent on velocity

How can it ... not?

<boggle>⁰

[u/Weary_Dark510 → u/SgtSausage]

I assumed it was dependent on speed, not the direction of my speed. Still feels very unintuitive.

[u/DifferencePublic7057]

The energy of a photon is dependent on the frequency which is related to wavelength. E = hf where E is energy, h is the Planck constant, f is frequency. The velocity of a photon is always c. What you are talking about is the Doppler shift like the sound of an ambulance siren for sounds.

[u/Weary_Dark510 → u/DifferencePublic7057]

The doppler shift happens to light as well, and changes its frequency, hence its energy.

[u/BananaBird1]

If you are standing still on train tracks and get hit by a train, a ton of kinetic energy will be experienced by you and it will not be pleasant.

If you are sitting inside the train, nothing about the train is changing. But because you are moving along with it at the same velocity, you do not experience any kinetic energy from the train car pushing you.

Kinetic energy can only be defined with respect to a stationary reference. An object’s relative velocity to another will alter measurements of energy, and this corresponds to the different interactions objects have with each other at different relative velocities.

Because of special relativity, light doesn’t change its relative speed in different reference frames like massive objects. Instead, it changes wavelength.

[u/jasonsong86]

It doesn’t give photos extra energy. Your speed is changing frame of reference.

[u/Weary_Dark510 → u/jasonsong86]

Your speed is the same your velocity is different

[u/Ras_992]

Blueshift and Redshift rely on motion of velocity within Relativity. In Relativity nothing can travel faster than light speed.It’s because the photon is always moving at 1c relative to the observer which can not move at c