Question

How fast would the Earth have to rotate so that it would neutralize gravity?

Asked by: Brad Nelson

 Answer

In order to neutralise the acceleration due to gravity the centripetal acceleration needs to be equal to the acceleration due to gravity:

Centripetal acceleration = 9.81 m/s2

The centripetal acceleration is, a:

a=r x w2

Where r is the Earth’s radius (in our case the radius at the equator), and w is the angular velocity.

Let a = 9.81 m/s2 and r = 6.4 x 106 m

9.81 = 6.4 x 106 x w2

Therefore w = 0.00124 rad/s

This is how fast the Earth would need to rotate to get centripetal acceleration at the equator equal to 9.81 m/s2.

So if we use this value in this equation:

w = 2/T

Where w is the same as before, the numerator is constant, and T is the time for rotation or the period.

If we put our value of omega (angular velocity) into the equation we find that T = 5074.99 seconds or 1.409 hours. This means that the Earth would need to rotate with a period of 1 hour 24 minutes. This means it would need to rotate approx. 20 times faster than it does now!

Answered by: Dan Summons, Physics Undergrad Student, UOS, Souhampton

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