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Doubt in Inertial frame of reference

  1. Aug 30, 2013 #1
    Newton's laws of motions are not applicable in Non-inertial frames of reference which means only mutually accelerated frames of references, My question is how can we apply Newton's laws of motions for practical experiments such as simple pendulum, motion of a ball, etc. conducted in near surface of earth

    I referred a book it says that orbital acceleration of the Earth is insignificant and the effect of the Earth’s rotation is normally a small correction, the earth may be assumed to be inertial frame.
    I know there is a reason we are assuming earth may be inertial frame, have some idea that it should be something regarding rotation of frame of reference, but i am unable to reason it precisely, Help me
  2. jcsd
  3. Aug 30, 2013 #2


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    Newtons laws can be applied in arbitrarily accelerating/rotating frames as long as you take into account the pseudo forces.
  4. Aug 30, 2013 #3


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    The surface of the Earth is indeed in an accelerating frame of reference, like when you are in a car speeding up. You feel a force pushing you back in your seat which is not due to anything pushing you in the car. It is because the car is accelerating and you are along for the ride. If you want to make Newton's laws work, you account for this by adding an extra force, a pseudo force into Newton's second law.

    On the Earth, this acceleration is barely noticeable on small scales, but you can see it for yourself with a Foucault Pendulum.
    On larger scales, it's a huge driving force in the weather, and why hurricanes spin in opposite directions in the northern and southern hemispheres (it's NOT enough of a force to cause toilets do drain in opposite directions; that's just the shape of the bowl and plumbing).
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