# Thread: Relative motion between me and Earth

1. Earth is rotating at constant speed, and everything on it, including me, move along with earth at the same speed. Suppose, I 'jump' from the ground, then the PHYSICAL CONTACT between me and the earth vanishes....... so in such a case, I should not be carried away along with the earth's speed in its direction in the few seconds of time while I am 'flying' in air. So, the ground below my feet should move ahead of me in its speed............I mean to say that, there should be relative motion between me and the ground for the period when I jump from the ground. BUT, this does not happen, I can't find any relative motion between me and the ground. In the same way, If an Helicopter flies, raises to an altitude from the ground and maintains the same position, then the earth below should move relative to the Helicopter. But id does not happen. WHY? CAN ANYBODY EXPLAIN THIS AND CLEAR MY DOUBT?

2.

3. There'd have to be some force accelerating (slowing) the helicopter with respect to the Earth. Otherwise it'll continue speeding along as it was, before, on the ground.

4. You still have the momentum that only decays due to friction. Not your position is conserved, but your momentum. For the same reason, space ports are more efficient the more they are towards the equator. The velocity is the largest there, and the momentum that any body has is already part of the escape velocity needed to launch rockets into space.

5. Let's turn the problem around. If a meteor was heading straight towards you when it was twelve hours from impact, where would you be when the impact occurred?

The meteor does not have any of Earths rotational momentum.

Your space-time coordinates are co-rotating with the Earth which is why it takes an input of energy to move from one location to another.

6. Originally Posted by nagakannanka
Earth is rotating at constant speed, and everything on it, including me, move along with earth at the same speed. Suppose, I 'jump' from the ground, then the PHYSICAL CONTACT between me and the earth vanishes....... so in such a case, I should not be carried away along with the earth's speed in its direction in the few seconds of time while I am 'flying' in air. So, the ground below my feet should move ahead of me in its speed............I mean to say that, there should be relative motion between me and the ground for the period when I jump from the ground. BUT, this does not happen, I can't find any relative motion between me and the ground. In the same way, If an Helicopter flies, raises to an altitude from the ground and maintains the same position, then the earth below should move relative to the Helicopter. But id does not happen. WHY? CAN ANYBODY EXPLAIN THIS AND CLEAR MY DOUBT?
Try this little experiment. Take a ball and hold it in your hand, palm downward. Move your hand rapidly forward and then let go of the ball while your hand is still moving. Does the ball drop straight down out of your hand when you let go, or does it continue to travel forward?

The ball continues forward due to its inertia. Objects at rest tend to stay at rest and objects in motion tend to stay in motion. The ball was moving forward with your hand when you let go. It wants to keep moving forward even after it has left contact with your hand. The same thing happens when you jump. You were moving in the direction that the Earth turned before you jumped, and you will want to continue that movement after you leave the ground.

7. This can be explained with the train analogy as well:

If you are on a train moving at a constant velocity of 20m/s, then you are also moving at 20m/s- because if you weren't you would have slammed into the back of the train and out the back (if there's a window).

Anyway, if you jump while on this train then you will land back in the exact same position as when you jumped. This is because even as your feet leave the train floor, you will still be travelling at 20m/s due to inertia and conservation of momentum and motion.

This applies to Earth, our solar system and the Milky Way galaxy as well. In truth, everything on Earth is moving at millions of miles per hour through the cosmos...

8. your question was one of the questions that i never had an answer for when i studied relative motion - at school - ....
but i used to try some simple experiments such as jumping in the elevator ! but still the conclusions weren't so clear ...
X(x-y) answer is convincing , however one of the things that i experienced is to measure the time needed for a trip - by plane - when you travel east or west for the same distance ..
there is a significiant difference ...
for instance ... when i travel from dubai - uae- to beirut - lebanon - ( from east to west )
the trip tooks about 3 hours ...
but when i come back from beirut to dubai ( west to east ) it tooks like 3 hours and a half ... the difference is about 30 minutes ...
isn't that interfering with what you said - or to be more specific with what i anderstood from what you said ! -
btw if what i said is like totally irrelevant to the whole topic ... please clarify for me

9. Originally Posted by sara azzam
your question was one of the questions that i never had an answer for when i studied relative motion - at school - ....
but i used to try some simple experiments such as jumping in the elevator ! but still the conclusions weren't so clear ...
X(x-y) answer is convincing , however one of the things that i experienced is to measure the time needed for a trip - by plane - when you travel east or west for the same distance ..
there is a significiant difference ...
for instance ... when i travel from dubai - uae- to beirut - lebanon - ( from east to west )
the trip tooks about 3 hours ...
but when i come back from beirut to dubai ( west to east ) it tooks like 3 hours and a half ... the difference is about 30 minutes ...
isn't that interfering with what you said - or to be more specific with what i anderstood from what you said ! -
btw if what i said is like totally irrelevant to the whole topic ... please clarify for me

The time difference you noted in most likely due to flying with and against the jet stream. Jet streams are high altitude air currents.

10. The difference in flying time may be due to the wind direction, or perhaps a different kind of airplane, but that is a different question than the one that was asked.

The principle we are discussing is called Galilean invariance or Galilean relativity. Here is how Galileo said it.
http://en.wikipedia.org/wiki/Galileo's_ship
Shut yourself up with some friend in the main cabin below decks on some large ship, and have with you there some flies, butterflies, and other small flying animals. Have a large bowl of water with some fish in it; hang up a bottle that empties drop by drop into a wide vessel beneath it. With the ship standing still, observe carefully how the little animals fly with equal speed to all sides of the cabin. The fish swim indifferently in all directions; the drops fall into the vessel beneath; and, in throwing something to your friend, you need throw it no more strongly in one direction than another, the distances being equal; jumping with your feet together, you pass equal spaces in every direction. When you have observed all these things carefully (though doubtless when the ship is standing still everything must happen in this way), have the ship proceed with any speed you like, so long as the motion is uniform and not fluctuating this way and that. You will discover not the least change in all the effects named, nor could you tell from any of them whether the ship was moving or standing still. In jumping, you will pass on the floor the same spaces as before, nor will you make larger jumps toward the stern than toward the prow even though the ship is moving quite rapidly, despite the fact that during the time that you are in the air the floor under you will be going in a direction opposite to your jump. In throwing something to your companion, you will need no more force to get it to him whether he is in the direction of the bow or the stern, with yourself situated opposite. The droplets will fall as before into the vessel beneath without dropping toward the stern, although while the drops are in the air the ship runs many spans. The fish in their water will swim toward the front of their bowl with no more effort than toward the back, and will go with equal ease to bait placed anywhere around the edges of the bowl. Finally the butterflies and flies will continue their flights indifferently toward every side, nor will it ever happen that they are concentrated toward the stern, as if tired out from keeping up with the course of the ship, from which they will have been separated during long intervals by keeping themselves in the air. And if smoke is made by burning some incense, it will be seen going up in the form of a little cloud, remaining still and moving no more toward one side than the other. The cause of all these correspondences of effects is the fact that the ship's motion is common to all the things contained in it, and to the air also. That is why I said you should be below decks; for if this took place above in the open air, which would not follow the course of the ship, more or less noticeable differences would be seen in some of the effects noted.

11. the speed in both trips is constant ... weather conditions - winds or whatever - are constant too ... even if they weren't for a certain trip ... in every summer vacation i travel and i measure the time the two trips spend ... and i get the same results ...

12. Originally Posted by sara azzam
for instance ... when i travel from dubai - uae- to beirut - lebanon - ( from east to west )
the trip tooks about 3 hours ...
but when i come back from beirut to dubai ( west to east ) it tooks like 3 hours and a half ... the difference is about 30 minutes ...
According to these schedules the trip from Dubai to Beirut takes a little longer, which is the opposite of what you experienced. The difference is only 5 minutes.

12:45 pm Depart Dubai (DXB)
Arrive Beirut (BEY) 3:05 pm Wed 11-Aug
Duration: 3hr 20mn Middle East Airlines 427
Nonstop flight

7:30 am Depart Beirut (BEY)
Arrive Dubai (DXB) 11:45 am Wed 11-Aug
Duration: 3hr 15mn Middle East Airlines 426
Nonstop flight
http://www.expedia.com/pub/agent.dll...=08/18&&rdct=1

http://www.expedia.com/pub/agent.dll...=08/18&&rdct=1

13. I'm not sure on that one, but I would've said that it all depends upon the jet stream like 'Janus' stated- I think it was Janus?

14. thanks harold ... mmm i don't know ... thats weird !

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