mjhjmtu

The other day, I found this puzzle laying on a floor:

This holds true. Why? $$w=2u$$

There was nothing else on it. It looked like an equation of some sort, although I had no clue about the $w$ and $u$ variables. It looks somehow related to physics, maybe a magical object that always has its weight be twice its speed? Can't be sure, and it looks like I have to prove it. Prove magic? Nah. Prove something so broad without any given assumptions? Meh.

I have been staring at this equation for hours, wondering what it may represent, but to no avail; nothing came up on my mind. Eventually, I quit, so I'm posting this here. Maybe folks can figure something out, I'm literally exhausted! I'll go get some rest now, and, in the meantime, you can freely express an answer if you've figured one out, just be sure to support it with a proof.

Possible solution:

Its not so much a physics or math formula as to do with letters. The formula is saying the letter w is 2 u's as is if you put 2 u's side by side you get a w. Its even in the naming u and double-u. Since there is the lateral thinking tag I think this could be the expected solution.

I am going to make one assumption: $w$ and $u$ are arbitrary and can be anything. As a result, this equation may be true because it is how the variables are defined.

$w$ is defined as being twice as much as $u$. That is why $w=2cdot u$.

After all, a definition of something is given to always be true. It's a self-satisfying rule.

The one major assumption here is that it is purely mathematical, as opposed to gabbo1092's more 'puzzling'-related answer.