# Interesting question

1. Sep 18, 2006

### unscientific

F=ma a = F/m Light's mass: 0 N = infinite acceleration?

2. Sep 18, 2006

### JesseM

Why is this on the relativity board? And if 0 N means "0 Newtons", ie F=0, this will mean a=0 for a finite mass, not a=infinity.

3. Sep 18, 2006

### DaveC426913

F=ma is Newtonian classical physics. Cannot apply to relativistic concepts.

4. Sep 24, 2006

### unscientific

light has 0 mass, and im talking about light being 0 mass here, jessem

5. Sep 24, 2006

### bernhard.rothenstein

light has zero rest mass!

6. Sep 24, 2006

### JesseM

But F=ma doesn't apply in relativity, although on this thread masudr mentioned that there is a similar equation relating the force 4-vector to the momentum 4-vector, $$f_{\mu} = \frac{d}{d\tau}p_{\mu}$$. Also, you said "0 N", I assumed the N was short for "Newtons", which is a unit of force, not mass.

Last edited: Sep 24, 2006
7. Sep 25, 2006

### actionintegral

This isn't even a physics question! Every sixth grader tries to divide by zero thinking the answer is infinity. This belongs in the homework section.

8. Sep 25, 2006

### JesseM

It is true in a sense in calculus, though--the limit of 1/N as N approaches zero is infinity.

9. Sep 28, 2006

### therapeuter

what i have heard is that photon, since it is already flying at the speed of light, cannot be slowed down. so it cannot be going slower than the speed of light and then accelerated to the speed of light. neither can it be accelerated from the speed of light beyond the speed of light. so F = ma has no application to light.

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