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Newton's first law

  1. Dec 8, 2007 #1
    newton's first law states that a body in motion tends to stay in motion and that's why when you're driving a car and then suddenly stop you get pushed at the same speed you were traveling.
    the earth orbits the sun at 64,000 miles and the earth's rotation is 1000 miles per a hour.
    my question is that how come that when astrountes leave earth they don't get pushed away at a speed of 64,000 miles per a hour.
    and the second question is that if theoretically earth would stop rotating will the object's on earth's surface will get "pushed" at a velocity of 1k miles per a second?
  2. jcsd
  3. Dec 8, 2007 #2


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    Astronauts do move at 64,000mph, but since the Earth is moving with them at 64,000mph, there is no difference. I mean, they would HAVE to move that fast in that direction to keep up.

    If Earth suddenly stopped, I'm pretty sure there would be something major going on which would change everything, but if it just happened to, everything on one side would be launched into space, everthing on the other would be squished into the ground. If it stopped rotating, everything would go outwards/upwards the same way rotating a bucket filled with water and suddenly stopping would, taking into account the effects of gravity.
  4. Dec 8, 2007 #3
    "The Shuttle travels about 5 miles per second give or take, which is 26,000 feet per second."

    the shuttle actully goes much slower.
    5X3600 = 18,000 mph.

    and about the earth rotation , say you're driving at a speed of 100{->} mph with the earth rotation then if you suddenly come to a stop you will fly at at a speed of 1100 mph { relative to space } , but then again if you go at 100{<-} againts the earth rotation , and then come to a stop aren't you suppose to get pushed at a velocity of 900 mph <- ?
  5. Dec 8, 2007 #4

    Doc Al

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    I don't know what you mean by "pushed at the same speed", but it doesn't work that way. If you're driving along and you suddenly stop the car (by arranging for the ground to push on the tires) you tend to keep going because you are not being pushed. It requires a force to change your motion, that's why you strap yourself in--so the seatbelt can exert a force on you to change your speed so you don't go flying through the windshield. So you're not being pushed forward, it just seems that way because the car is being pushed back.

    If you're on the equator, then your speed with respect to the center of the earth is roughly about 1000 mph. If you're driving along at 100 mph in the direction that the earth rotates (towards the east), your speed would be 1100 mph with respect to the earth's center.

    If, by some magic, the earth just suddenly stopped rotating you'd keep going at your speed of 1100 mph until gravity, friction, and collisions began exerting their forces on you and slowed you down.
    Last edited: Dec 8, 2007
  6. Dec 9, 2007 #5
    No, actually it's the opposite way around, gravity would just become a little stronger at the equator. The difference is not really noticeable (about 1% or something). We wouldn't notice any other effect.

    opps, we'd only have one day per year. That would be the only really noticeable difference for us.

    If Earth stopped orbiting the Sun we'd all fall into the Sun, that's all. There would be no more Christmases, New Years, or summer holidays...
  7. Dec 9, 2007 #6


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    The space shuttle doesn't have brakes! In a car, you get thrown forward (in the car's reference frame) because the car stops. When an astronaut leaves earth, they aren't stopping with respect to the earth's motion around the sun - that would require a lot of power from their engines.
    Stop with respect to what? The only thing your car's brakes and wheels can apply a force on is the ground, so they can only stop with respect to the ground. To stop with respect to an arbitrary outside reference frame would require some other means of applying a force (such as a rocket engine).
    Last edited: Dec 9, 2007
  8. Dec 9, 2007 #7


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    DST was actually talking about the immediate effect of if the earth *suddenly* stopped rotating and we didn't. We'd still be moving forward at 1000 miles per hour.
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