- #1
PleaseSpeakSlowly
- 7
- 1
Hi everyone. Please be gentle with me, I am not a physicist! I am a layperson with an interest in learning more, and I’m reading a book called ‘How to Teach Relativity to Your Dog’ by Chad Orzel. It’s supposed to be physics for dummies, but it’s clearly not dumbed down enough for me because there’s something I’m really struggling with!
In the section about converting between different frames of reference, the author explains that the coordinates for measuring position are x for east-west direction, y for north-south, z for up-down and t for time. He then gives coordinates for three measurements made from two different frames of reference, Emmy’s and Nero’s:
Emmy:
(t = -1s; x = -10m; y = -10m; z = 0m)
(t = 0; x = 0m; y = -10m; z = 0m)
(t = +1s; x = +10m; y = -10m; z = 0m)
Nero:
(t = -1s; x = +10m; y = +10m; z = 0m)
(t = 0; x = 0m; y = +10m; z = 0m)
(t = +1s; x = -10m; y = +10m; z = 0m)
He goes on to say:
“If you play around with these numbers a little, you can come up with a simple recipe for converting between Nero’s measurements and Emmy’s: you simply take the east-west coordinate measured by Nero, and subtract his speed (10 m/s) multiplied by the time. A little more fiddling around will show you that getting from Emmy’s measurement to Nero’s involves just the reverse: you take the east-west coordinate measured by Emmy, and add to it Nero’s speed multiplied by the time. In this way, you can take any measurement made by Nero and convert it into a measurement that will make sense to Emmy, and vice versa.”
No matter how much I try, I can’t get from one frame of reference to the other by following these directions. I’m clearly missing something very obvious! Could anyone shed some light?
In the section about converting between different frames of reference, the author explains that the coordinates for measuring position are x for east-west direction, y for north-south, z for up-down and t for time. He then gives coordinates for three measurements made from two different frames of reference, Emmy’s and Nero’s:
Emmy:
(t = -1s; x = -10m; y = -10m; z = 0m)
(t = 0; x = 0m; y = -10m; z = 0m)
(t = +1s; x = +10m; y = -10m; z = 0m)
Nero:
(t = -1s; x = +10m; y = +10m; z = 0m)
(t = 0; x = 0m; y = +10m; z = 0m)
(t = +1s; x = -10m; y = +10m; z = 0m)
He goes on to say:
“If you play around with these numbers a little, you can come up with a simple recipe for converting between Nero’s measurements and Emmy’s: you simply take the east-west coordinate measured by Nero, and subtract his speed (10 m/s) multiplied by the time. A little more fiddling around will show you that getting from Emmy’s measurement to Nero’s involves just the reverse: you take the east-west coordinate measured by Emmy, and add to it Nero’s speed multiplied by the time. In this way, you can take any measurement made by Nero and convert it into a measurement that will make sense to Emmy, and vice versa.”
No matter how much I try, I can’t get from one frame of reference to the other by following these directions. I’m clearly missing something very obvious! Could anyone shed some light?