# Homework Help: Massive particles are relativistic particles if their speed...

1. Mar 23, 2016

### amyy

1. The problem statement, all variables and given/known data
Massive particles are relativistic when their kinetic energy is comparable to or greater than the energy corresponding to their rest mass. (This condition implies that their speed is close to the speed of light.)
But what does the comparable mean? Is it that the particle whose speed is more than 0.1c must take the relativistic effect into account?

2. Relevant equations

3. The attempt at a solution

Thank you!

2. Mar 23, 2016

### Ray Vickson

3. Mar 24, 2016

### amyy

This is from the Wikipedia https://en.wikipedia.org/wiki/Relativistic_particle

You said it depends on accuracy, could you give me an example please? If the 36Ar18+ is accelerated up to some certain speed, we will consider relativistic momentum when we calculate the magnetic rigidity:$B\rho=p/q=mv\gamma/q.$

4. Mar 24, 2016

### Physics-Tutor

HI Amy, Ray is correct. All depends on the error you are willing to consider

It might be relevant to neglect the Rel. effect or not depending on what you are trying to achieve.

For example, you can calculate the fraction of the speed of light for which you have to take into account relativistic effects, given a certain experimental framework.

You can set the threshold of difference you need. Say, I consider 1% as being the threshold above which I will consider relativistic effects for KE. I can calculate by solving this:

With
and and

(where m is the rest mass).

The value you find for , allows you for instance to determine from what speed you need to be considering relativistic effects based on the threshold you chose from the error in your experimental data.

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5. Mar 27, 2016

### amyy

Physiscs-Tutor, hello
I see your point, thank you very much for explaining it to me

6. Mar 31, 2016

### ProfuselyQuarky

You can use the LaTeX editor, you know. Just thought I'd tell you in case you didn't know, and was getting annoyed with attaching images

$KE_{rel} =(\gamma-1)mc^2$
Code (Text):
KE_{rel} =(\gamma-1)mc^2

7. Mar 31, 2016

### Physics-Tutor

Thank you ProfuselyQuarky, I'll definitely check it out... :-) Could be a less painful than typing the equation in word, capturing pictures and posting them in my posts!

8. Mar 31, 2016

### ProfuselyQuarky

Totally! Give it a try!