# What is the length

1. Dec 24, 2011

### Snip3r

Consider a rod of length 1 m and I are in frame S. Now i move at a velocity considerable to velocity of light wrt S. I take the rod with me (with its length parallel to motion). Now when i measure the length of the rod what will it be?i think it will still be 1 m for me but just wanted to confirm

2. Dec 24, 2011

### Staff: Mentor

Yes, since the rod remains at rest with respect to you, you'll measure it to have its rest length of 1 m.

3. Dec 24, 2011

### Qzit

Hi Doc Al

If you shoot light out from the rod in a perpendicular direction to the space ship does it remain perpendicular when it hits the space ship? Does the distance matter?

4. Dec 24, 2011

### Staff: Mentor

As seen by observers in the spaceship, the light path is perpendicular to the rod and the ship.
What distance?

5. Dec 24, 2011

### Naty1

Doc Al...how did you ever interpret this??
Is the 'perpendicular' to the rod or the spaceship or both? What direction is the spaceship moving relative to the rod? Is it accelerating or moving with a constant velocity [fixed speed and direction]?

if the ship is moving at constant velocity parallel to the rod, right??

6. Dec 24, 2011

### HallsofIvy

Staff Emeritus
I can't speak for Doc Al, but I assumed that the "space ship" Qzit was referring to was the one on which the Snip3r was carrying the rod. Since they are all (Snip3r, the rod, and the spaceship) are all motionless with respect to each other, it really does not matter whether is arranged in the direction the space ship is moving.

7. Dec 24, 2011

### Naty1

8. Dec 24, 2011

### Naty1

HallsofIvy...oh good grief, no wonder...I did not think of that scenario....
Thank you!!!

That also answers my post #7....
and to all a good night!!

But that thread relates...a different perspective...so I'll leave it....

9. Dec 24, 2011

### Staff: Mentor

Exactly. (If Qzit wants to discuss a different scenario, let him define it.)

10. Dec 24, 2011

### HallsofIvy

Staff Emeritus
The discussion in that link doesn't seem to have anything to do with this topic. There, you are moving at high speed relative to a mirror and shining as light at it, here, you are measuring a stick you are carrying with you.

11. Dec 27, 2011

### Naty1

i agree... that's why I said a "different perspective" above ...maybe I should have said different frames of reference or different situation.