Hi,
This has been bugging me since i was very young… If one was to travel around the world, setting off say on monday about 12pm, with the sun directly above their head at all times, and each town they came to they asked what day and time it was. When they arrive back to their starting point and asked what day and time it was the answer would be tuesday 12pm…at what point did it become tuesday for the person travelling around the world? Surely, because they travelled with the sun directly above their head…it remained monday 12pm at all times…
and another thing…
If one was to dig a hole right through the earth, from one pole to the other… what would happen if they jumped into it? Would they eventually come to rest in the center or what?
I have a few more, but i think even Cecil will struggle with these two
Guess again. And welcome to the boards. Your question about the date changing is the clearest expression of why we need the International Date Line I’ve come across. I’m going to have to remember it.
Nuh-uh! If you go around the world fast enough, eventually you can make it stop rotating, and even start travelling backwards in time! Superman’s done it. And, to be completely honest, I trust Superman more than I trust Cecil.
I take it we’re ignoring the fact that you’d probably melt before you get to the centre
What would happen is that you’d oscillate aroound the centre of the Earh.
The reason for this is (here comes the maths!) that the gravitational force, which is what pulls you to the centre of the Earth is proportional to the mass of the Earth which is directely below you, and inversely proportional to how far you are from the centre of the Earth. So, as you hurtle towards the centre of the Earth, the force acting on you decreases, until you get to the centre, where there’s zero force acting on you. But, you’ve still got momentum, so you don’t stop. Instead you carry on through the centre of the Earth, slowing down, until Earth’s gravity stops you. But then, there’s a force acting on you trying to drag you down to the centre of the Earth again, so you go throough the entire thing all over again. Ignoring air resistance (stupid thing to do, but hey, it makes the maths easier!), you’ll carry on doing this ad infinitum…
Right and IIRC the period of your motion is approximately 90 minutes, which, not coincidentally, is the time it takes a geosynchronos satelite to do one orbit.
Um, no. Anything in low earth orbit, like the ISS or Hubble, takes about 90 minutes. To be geosynchonous, i.e., have a period of 24 hours, your orbit has to be 22,300 miles above the earth. If this orbit is above the equator, the satellite appears to stay in the same place and the orbit can be called geostationary.
Urp! Of course you are right. I cringe in shame. I can’t even spell. The period is the same as if it were in orbit at earth’s surface and there were no air resistance. And of course, the motion through the center also depends on that.
So if the IDL didn’t exist, you could get back at exactly the same moment you left. Which means the line costs me a day of my life. Bummer. Who went and put that thing there, anyway?
Peace,
mangeorge
