# Does the density of a stick change according to special theory of relativity? Provided the stick is moving at nearly the speed of light? [closed]

The equation in the image made me think of the density case in special theory of relativity !

• It would be helpful if you could actually write a question rather than just posting an equation. – ZeroTheHero Feb 7 '19 at 22:56

Sure it does. If the stick has a linear density $$\lambda=m/x$$ where x is the length, then if it's moving at velocity $$v$$ away from you, the length would appear to be:

$$x'=\frac{x}{\gamma}$$

where:

$$\gamma=\frac{1}{\sqrt{1-(v/c)^2}}$$

the, the density measured by the observer would be:

$$\lambda'=\lambda\gamma$$

And because $$\gamma>1$$, it would appear to be more dense.