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Consider my example below. Example: 1. A man standing on grass(point) on earth surface. 2. He jumped. 3. And returned back, and he could find the same grass(point) under his foots. Right?

If earth is spinning, when he is on air (on jump) and return back to the earth surface, the grass(point) should be moved right or left side based on rotating direction of earth Right. But it did not happen on real scenario.

Newton told that as "Gravity". and the definition would be the force that attracts a body towards the centre of the earth, or towards any other physical body having mass.

But from my example the man attaching with a earth surface by some force due to not only of earth's massive body, but also for it's spinning.

Because If gravity only about to mass means the man return back to earth surface is OK, but how could he feel like settle down on same place on earth surface that he stood before he jumps.

I am really curious about the answer.

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  • $\begingroup$ Essentially a duplicate of physics.stackexchange.com/q/48287/2451 , physics.stackexchange.com/q/80090/2451 , physics.stackexchange.com/q/137191/2451 , physics.stackexchange.com/q/1193/2451 and links therein. $\endgroup$
    – Qmechanic ♦
    Commented Aug 4, 2015 at 18:13
  • $\begingroup$ Suppose you are traveling on a bus at 30 mph, and you are standing up. Now you jump straight up. Where do you land? The man on the grass is also on a bus, that is traveling 1000 mph to the east. In fact he is traveling 70,000 mph to get around the sun in 1 year. In fact he is traveling 5 times that around the center of the galaxy. Who knows how fast the galaxy is traveling, relative to others? $\endgroup$
    – Mike Dunlavey
    Commented Aug 4, 2015 at 18:20
  • $\begingroup$ @Mike Dunlavey I cannot get your point clearly. Could you please read the comments I added with the Jahan claes and tell me if I am wrong about my intuition. Thanks. And as it give some additional info, it is not a duplicate question. $\endgroup$
    – Saravanan
    Commented Aug 5, 2015 at 5:09
  • $\begingroup$ @Saravanan: 1) You are courageous to try to write this much English when it is not your first language. 2) Still, I am having difficulty understanding your intuition. I understand a person doing a vertical jump and landing in the same place relative to a moving earth. You seem to see a difficulty with this, and I do not. $\endgroup$
    – Mike Dunlavey
    Commented Aug 5, 2015 at 12:20
  • $\begingroup$ @Mike Dunlavey: Did you read comments attached with Jahan's answer below. In conclusion, From your comments also I can only understand that there is a force(caused by earth spin) only attaching objects with earth. Since we are attach with earth we are also spinning (travelling) in earth speed. So only he could come back to his previous state. Right? So here I cannot see any definition of gravity(obj in higher mass pulls mass in lower). The man came down because he attracted or pulled force caused by earth spin. Is it correct? $\endgroup$
    – Saravanan
    Commented Aug 5, 2015 at 13:27

1 Answer 1

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What you have to realize is, both the man and the ground beneath him are travelling at the same speed. What that means is, yes, the ground underneath the man is travelling east very quickly, but the man is also travelling east just as quickly.

The gravitational force causes the man to come back down, but it has nothing to do with making sure he stays over the same point on the earth's surface. He will ALREADY stay over the same patch of earth, due to his speed eastward.

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  • $\begingroup$ Folks please understand my question clearly and erase the existing definition about gravity prior to answer it. To return back to the same place (on grass here) there are two consideration 1. Mass 2. The man always attaching with the spinning earth with force due to spinning. even the man is in air he is attached still with that force..and he will be ditached when he travel crossing the limit of the force due to spinning. Everything seems to be perfect here without gravity.. I cannot agree the definition of gravity here. $\endgroup$
    – Saravanan
    Commented Aug 4, 2015 at 19:38
  • $\begingroup$ @Saravanan I think the important thing to understand is that gravity has nothing to do with pulling the man eastward. Perhaps a simpler example: if you're on a fast-moving train and jump, you'll land in the same place you jumped from. Gravity doesn't make you "stay with the train" at the same spot you jumped from. It's just that you already had the same velocity as the train when you jumped! Thus, nothing needs to give you velocity in order to stay in the exact same spot. $\endgroup$
    – Jahan Claes
    Commented Aug 4, 2015 at 19:51
  • $\begingroup$ For me it seems gravity is not at all be a force. Why?Which makes me to think like this. 1. we should not stand near to running train. ok. Now you yourself assume that train track as circle. people stand near to moving train at platforms. What would happen now? people standing in circular platform will feel like they are attracted by train, in this case Right? Now assume train moving circular path is EARTH and people around that is standing in SPACE. Example in my question same as like this, Right. $\endgroup$
    – Saravanan
    Commented Aug 5, 2015 at 4:48
  • $\begingroup$ The man is on air(while he jumps)is still attaching with a spinning earth.Since he is a movable object he could jump.Even he is able to jump, he is sill within a force that is similar like distance between running train and people in platform.That force caused by spinning earth, but when he crossed that boundary of that force,he will feel earth is spinning but he is in rest that is similar like people stand far to the running train.So conclusion is we are attached with the earth not only relative of MASS but also relative to the earth spinning.As def for gravity failed here,its not a force $\endgroup$
    – Saravanan
    Commented Aug 5, 2015 at 5:05
  • $\begingroup$ Here is a link that added value for my intuition. Einstein also felt difficult while relating his relativity theory to the newtoniam gravity and felt that there is no force as GRAVITY actually. According to Einstein E=mc^2, we need energy E to move object with mass m to a light speed c(velocity limited to light speed here). Newton also state that F=ma, we need force F to move object with mass m to some acceleration a. Both left some points here which is important here.I will continue this scenario with next comment. $\endgroup$
    – Saravanan
    Commented Aug 5, 2015 at 10:00

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