Density of the block will increase as d = m/v
so as mass increases with increasing velocity and length is lorentz contracted
thus both factor will lead to increase in density

I can’t find any better way to represent space and time in one frame…. Spacetime diagram is cool

Well If the base ball is moving with constant velocity, then we can use this method else it will be a tedious calculation

Day and Night, Foucault pendulum

yes teaching does help, as Richard Feynman said it if you want to be expert in something, teach it.

The distinction between the past, present and future is only a stubbornly persistent illusion. As said by Albert Einstein.

What speed do we need to attain if we really want to feel the motion of earth?