Recent content by Caneholder123

I realize that. Can you help me with the setup of the problem?

Considering the approximations that the camera is far away from the bullet and that the bullet is right in front of the ruler, projection is just the length measured from the camera reference frame. And that length is \frac {l_0}{\gamma} because the motion is just in one direction.

No, m8. I don't get it. Doesn't the bullet move only move in x-direction in camera reference frame too, or I am not reading this properly? Sorry for being late with the reply, I was extremely busy last two days.

I didn't position the camera reference frame right. Thank you for the help.

1. A distant camera is taking an image of a bullet of proper length l_0 and velocity v. The bullet is moving on a straight line which is parallel to the ruler (a bit behind the bullet, when it is watched from the camera). An angle between the velocity vector and the line that connects the camera...

Thank you very much for the help!

This kind of thinking is new to me. I am not sure that I completely understand this, probably because I am stuck with kgs and Joules. Does this mean that we fix mass to some value, let's say 10 of something and then we define energy to be -20*m*(some unit speed squared)?

Starting from the equations of motion, show that the "vector of speed" of particle \vec V = (t', \vec r') (where the symbol ' is used for differentiation in respect to s) lies on the 4D sphere. Determine the center and radius of that sphere. s is defined with the following relation \frac...

t' is defined in the problem I have to solve as r, and that makes the units in that context OK, but V^2 still remains after calculation is done. John Baez writes about this in his http://blog , and he defines m=1, E=-1/2 and k=1, and that solves the problem. I am not familiar with this...

This is the link to the relevant paper. I have to show that vector (t', x', y', z') lies on the sphere. But for that to be, V^2 has to be 1 according to the equation in the introductory part of the section 2. That, by definition, means that E=-m/2. What does that mean, and why is this solution...