<p>I think it is referring to the speed and Lorentz factor $(\beta = v/c$ and $\gamma = [1-\beta^2]^{-1/2})$ of the gas as a whole. Within the gas, there could be particles moving with a variety of velocities.</p>

<p>So if you pick up a ball of gas at 10,000 K (ouch) and throw it at 100 m/s then the bulk speed is 100 m/s, but obviously the particles in the gas have their own individual velocities.</p>

CC BY-SA 3.0
2015-11-21T10:15:39.890Z
2015-11-21T10:15:39.890Z
ProfRob
<p>When we are talking about relativistic motions, say from a relativistic jet, what is meant by the term "bulk Lorentz factor", and the bulk speed, $\beta$?</p>

<special-relativity><high-energy-astrophysics>
What is the bulk Lorentz factor?
MichaelJRoberts
# What is the bulk Lorentz factor?

(Asked by: username_0 on 2015-10-16)

When we are talking about relativistic motions, say from a relativistic jet, what is meant by the term "bulk Lorentz factor", and the bulk speed, $\beta$?

**Tags:** special-relativity, high-energy-astrophysics

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## 1 answers

### Answer by username_1 on 2015-11-21. Score: 5 | Accepted answer

I think it is referring to the speed and Lorentz factor $(\beta = v/c$ and $\gamma = [1-\beta^2]^{-1/2})$ of the gas as a whole. Within the gas, there could be particles moving with a variety of velocities.

So if you pick up a ball of gas at 10,000 K (ouch) and throw it at 100 m/s then the bulk speed is 100 m/s, but obviously the particles in the gas have their own individual velocities.


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