Can energy conservation be violated?

AI Thread Summary
The discussion centers on the concept of energy conservation, particularly in relation to the Doppler effect and photon energy. A participant argues that the energy of a photon increases when emitted from a moving train and reflected back, suggesting that this occurs without any work being done. However, others clarify that energy is conserved in this scenario, as the mirror experiences a transfer of energy and momentum when reflecting the light. The consensus is that energy cannot be created or violated, and the energy observed is consistent across different reference frames. Overall, the discussion reaffirms the principle of energy conservation in physics.
Ironman1998
Messages
1
Reaction score
0
I think energy can be created...i agree that energy is not conserved between different reference frames..but i can show you that energy measured in a single frame may wary... Does photon's energy increase when i emit it from a train which is moving at comparable speed and get it reflected back by a mirror on a platform so that i can catch it again in the train? According to doppler effect the frequency of the photon for an observer standing near the mirror is greater to an observer in the train.So to the observer near the mirror, energy of the photon is greater than the energy observed by an observer in train.Similarly when it gets reflected back and reaches the train its frequency is larger than the initial frequency when observed by an observer in train .So obviously energy of photon is increased without doing any work...please correct me if i am wrong somewhere
 
Physics news on Phys.org
Ironman1998 said:
I think energy can be created
No it can't.

Ironman1998 said:
So obviously energy of photon is increased without doing any work...please correct me if i am wrong somewhere
The light bounces off the mirror, and there is energy and momentum transfer there. In the frame of the train the mirror is moving towards the train and is slightly slowed by the reflection. Its kinetic energy is carried away by the light.

[Mentors' note: This post has been edited to remove a loose end from when it was moved from another thread]
 
Last edited by a moderator:
  • Like
Likes Dale
Ironman1998 said:
So obviously energy of photon is increased without doing any work...please correct me if i am wrong somewhere
As @Ibix mentioned, the mirror is the source of the additional energy. Recall that light exerts pressure on a surface. This pressure reduces the speed of the mirror and thereby transfers both energy and momentum to the light. Energy is conserved in this case.
 
Last edited:
Answer to the title question: No.

Follow-up: Do you really think that millions of scientists and engineers over the past hundred years could plausibly have all missed something so obvious?
 

Thread '1:1 versus 2:1 Mechanical Advantage debate'

The rope is tied into the person (the load of 200 pounds) and the rope goes up from the person to a fixed pulley and back down to his hands. He hauls the rope to suspend himself in the air. What is the mechanical advantage of the system? The person will indeed only have to lift half of his body weight (roughly 100 pounds) because he now lessened the load by that same amount. This APPEARS to be a 2:1 because he can hold himself with half the force, but my question is: is that mechanical...
View full post »

Thread 'Newton's first law?'

Some physics textbook writer told me that Newton's first law applies only on bodies that feel no interactions at all. He said that if a body is on rest or moves in constant velocity, there is no external force acting on it. But I have heard another form of the law that says the net force acting on a body must be zero. This means there is interactions involved after all. So which one is correct?
View full post »
Thread 'Beam on an inclined plane'

Thread 'Beam on an inclined plane'

Hello! I have a question regarding a beam on an inclined plane. I was considering a beam resting on two supports attached to an inclined plane. I was almost sure that the lower support must be more loaded. My imagination about this problem is shown in the picture below. Here is how I wrote the condition of equilibrium forces: $$ \begin{cases} F_{g\parallel}=F_{t1}+F_{t2}, \\ F_{g\perp}=F_{r1}+F_{r2} \end{cases}. $$ On the other hand...
View full post »

Similar threads

Conservation of energy in a CM system moving at constant velocity
Replies
2
Views
1K
Train Conservation of Energy Question
Replies
17
Views
3K
Can We Do Better Than Mechanical Energy Conservation?
Replies
9
Views
3K
Influence of vacuum in the Conservation of energy
Replies
39
Views
3K
Energy conservation and friction
Replies
4
Views
1K
I Photon in a mirrored box moving in direction of travel
Replies
26
Views
2K
Violation of conservation of energy?
Replies
2
Views
2K
What Happens to Momentum in Non-Conserved Scenarios?
Replies
22
Views
4K
Bicycles: Question about Energy Conservation
Replies
9
Views
1K
Confusion about conservation of energy vs. momentum
Replies
3
Views
2K

Hot Threads

Recent Insights

Back
Top