# Presumed mass content of photon as gravitational source

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1. Feb 10, 2016

### DaTario

Hello,

I have read some of the posts which discuss the meaning and mistakes involving the equation:
$m_0 = \frac{h f }{c^2}.$

My question has to do with gravitation. I would like to know if it is correct to associate to a photon with frequency f, crossing a region near a mass M, a gravitational influence based on the "photon's mass content" above described (even if the concept of rest mass is not applicable).

Best wishes,

DaTario

2. Feb 10, 2016

### Staff: Mentor

That doesn't work. The effect is more similar to an object with twice the mass, but you still have non-negligible effects from the fast motion that doesn't allow to apply Newton's formula for example.

3. Feb 10, 2016

### DaTario

But near the surface of the earth, for example, being a region where we can approximate de gravitational force on a mass m to mg, and which implies that all bodies will fall with the same acceleration g, the photon will also behave like this, isn´t it?
I recall an interesting exercise proposed by Paul Hewitt in Physics Teacher magazine, in which he asks for a comparison between the fall of a ball and a beam of laser light, both bouncing back and forth in perfectly reflecive walls.

4. Feb 12, 2016

### DaTario

Just for the sake of good references, in the previous post (#3) I attached an illustration by Paul Hewitt, relative to the very problem I cited.