<p>First a conceptual thing: There's no 'taking out' the reference frame. Only changing it.<br>
Next: Velocity $\dot x$ is the change of position $x$, thus this is a coordinate-dependent quantity.  </p>

<p>Then mass is a bit more complicated, as there are two concepts of mass: <strong>Inertial</strong> mass and <strong>gravitational</strong> mass.<br>
Inertial mass is the proportionality constant between an acting force $\vec F$ on a body and it's change of velocity $\ddot x$, thus we get Newton's 2nd law that states $\vec F = m \ddot x$. Thus inertial mass is coordinate-independent by construction. Similar for the gravitational mass.<br>
Then experiments show that inertial and gravitational mass are equal, also there are <a href="https://en.wikipedia.org/wiki/Equivalence_principle" rel="nofollow noreferrer">theoretical reasons to believe this.</a> Thus we can show that mass in total is coordinate independent.</p>

CC BY-SA 3.0
2017-01-03T16:38:58.960Z
2017-01-03T16:38:58.960Z
AtmosphericPrisonEscape
<p>Would inertia not grow if we took out the reference frame?</p>

CC BY-SA 3.0
2017-01-03T16:40:49.970Z
I'm voting to close this question as off-topic because it is about physics, not astronomy. I'd recommend moving it to [Physics Stack Exchange](http://physics.stackexchange.com/), if you can clarify what you mean by "took out the reference frame".
HDE 226868
CC BY-SA 3.0
2017-01-03T17:14:59.593Z
reference frame, here https://www.youtube.com/watch?v=YVx5oraPWXk&t=2s
s1w_
<mass><velocity>
If velocity is relative, why mass (inertia) is increasing absolutely?
s1w_
# If velocity is relative, why mass (inertia) is increasing absolutely?

(Asked by: username_0 on 2017-01-03)

Would inertia not grow if we took out the reference frame?

**Tags:** mass, velocity

> **Comments:**
> **username_1**: I'm voting to close this question as off-topic because it is about physics, not astronomy. I'd recommend moving it to [Physics Stack Exchange](http://physics.stackexchange.com/), if you can clarify what you mean by "took out the reference frame".  
> **username_0**: reference frame, here https://www.youtube.com/watch?v=YVx5oraPWXk&t=2s  

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## 1 answers

### Answer by username_2 on 2017-01-03. Score: 1 | Accepted answer

First a conceptual thing: There's no 'taking out' the reference frame. Only changing it.  
Next: Velocity $\dot x$ is the change of position $x$, thus this is a coordinate-dependent quantity.

Then mass is a bit more complicated, as there are two concepts of mass: **Inertial** mass and **gravitational** mass.  
Inertial mass is the proportionality constant between an acting force $\vec F$ on a body and it's change of velocity $\ddot x$, thus we get Newton's 2nd law that states $\vec F = m \ddot x$. Thus inertial mass is coordinate-independent by construction. Similar for the gravitational mass.  
Then experiments show that inertial and gravitational mass are equal, also there are [theoretical reasons to believe this.](https://en.wikipedia.org/wiki/Equivalence_principle) Thus we can show that mass in total is coordinate independent.


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