- #1

- 3

- 0

On the above one minute physics video, the guy explained E=mc

^{2}using the idea of Doppler effect, but that doesn't seem right to me, can anyone help?

Thanks very much!!!

- Thread starter leolee5633
- Start date

- #1

- 3

- 0

On the above one minute physics video, the guy explained E=mc

Thanks very much!!!

- #2

mfb

Mentor

- 34,978

- 11,164

- #3

- 3

- 0

Thank you, but is that guy correct in calculating the Doppler energy gain to be (1+v^2/2c^2) not (1-v^2/2c^2)?

Also he is using classical kinetic energy to derive the formula, is that appropriate?

- #4

mfb

Mentor

- 34,978

- 11,164

That is a bit sloppy, he should integrate over all emitted photons / space directions.but is that guy correct in calculating the Doppler energy gain to be (1+v^2/2c^2) not (1-v^2/2c^2)?

That is another problem - you can derive that the classical formula does not work, but it is problematic to derive a new formula, based on the (wrong) old one. The result happens to fit, but that could be just by chance.Also he is using classical kinetic energy to derive the formula, is that appropriate?

- #5

- 3

- 0

I see, thank you very much for you help.That is a bit sloppy, he should integrate over all emitted photons / space directions.

That is another problem - you can derive that the classical formula does not work, but it is problematic to derive a new formula, based on the (wrong) old one. The result happens to fit, but that could be just by chance.

- Last Post

- Replies
- 10

- Views
- 2K

- Replies
- 11

- Views
- 2K

- Replies
- 5

- Views
- 498

- Replies
- 392

- Views
- 26K

- Last Post

- Replies
- 5

- Views
- 3K

- Replies
- 2

- Views
- 2K

- Replies
- 3

- Views
- 1K

- Replies
- 8

- Views
- 2K

- Replies
- 17

- Views
- 3K

- Last Post

- Replies
- 4

- Views
- 2K