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Why is the earth not moving

  1. Jul 8, 2013 #1
    I found that earth rotates with a speed of 465.1 m/s.So if i take a jetpack and stand floating in air why can't i see the earth rotating below me??
     
    Last edited: Jul 8, 2013
  2. jcsd
  3. Jul 8, 2013 #2

    russ_watters

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    1. Acceleration (Newton's 1st Law).
    2. Wind.
     
  4. Jul 8, 2013 #3
    i have not understood what do you mean by acceleration.
     
  5. Jul 8, 2013 #4
    Because as you go up, you still have that rotationspeed with you. As you move up, there is only a change in vertical speed (up/down), not in horizontal speed (the rotation of the earth).

    It's like jumping in a train, the train doesn't 'move' beneath you.
     
  6. Jul 8, 2013 #5

    russ_watters

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    You start off moving along with the earth's surface. In order to gain a speed of 465 m/s with respect to the earth's surface, you have to accelerate.
     
  7. Jul 8, 2013 #6
    thats because you are also moving at the same rate, while walking through a ball up, does it fall back or in your hand again??

    But i did not understand what russ watters meant by acceleration ???!!!
     
  8. Jul 8, 2013 #7

    sophiecentaur

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    This could be confusing, I think. What you mean is that, at some stage, you (or the various bits of your body) had to have been accelerated to the same speed as the surface of the Earth (which, of course, also had to be accelerated), Bottom line is that both are travelling at the same speed (velocity, actually) when the jump occurs - so they will keep moving together, despite lack of actual contact.

    This was a problem that Newton etc. had to deal with when people said that the Earth couldn't be rotating or we'd all be blown off our feet by the (static) air we are travelling through. Reasonable idea but wrong!!
     
  9. Jul 8, 2013 #8

    D H

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    Newton's first law, which says that an external force is needed to change the velocity of some object. Without that external force, there is no acceleration, no change in velocity.

    Newton's first law goes against the grain of everyday common sense. Common sense tells us that a force is needed to keep an object moving. Suppose you are pushing some object across the floor. Stop pushing for one instance and the object comes to a stop. Our everyday world apparently is one of Aristotelian physics.

    Students need to notch up their way of looking at the world so that Newtonian mechanics becomes common sense thinking. The reason that that pushed object comes to a stop is not because objects have a natural tendency to be at rest, the Aristotelian POV. It's because of friction. It's an external force is responsible for the change in velocity. With no external forces, the natural tendency is to continue going along at a constant velocity. That's Newton's first law.
     
  10. Jul 8, 2013 #9
    I Do understand Newtons Laws well, but how do you connect acceleration as an answer to the above question.

    I believe here we are interested relative velocity, the notion of inertia is to impress the fact that we are moving with the same speed as the earth, so we cannot make out the difference. Where does acceleration feature here!!
     
  11. Jul 8, 2013 #10

    D H

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    No acceleration means no change in velocity, and vice versa.
     
  12. Jul 8, 2013 #11
    ok I get it, you meant No acceleration!!! :smile:
     
  13. Jul 8, 2013 #12
    got it

    thanks
     
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