If the variation in g between one's head and feet is to be less then 1/100 g, then, compared to one's height ,what should be the minimum radius of the space habitat?

Let the habitat radius be R and the person's height be H.

Assume that the "gravity" is established by rotating a cylindrical or wheel shaped space station, with radius R. The actual value of g will be deterimned by the rotation rate, w.
g = R w^2.

g(head)/g(feet) = 1.01
= R(head)/R(feet)
= (R + H)/R = 1 + (H/R)

H/R = 0.01
R = 100 H (or higher)

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To calculate the minimum radius of the space habitat required for the variation in gravitational acceleration (g) between one's head and feet to be less than 1/100 g, we need to use the concept of centripetal acceleration.

Centripetal acceleration (ac) is the acceleration experienced by an object moving in a circular path. In the case of a rotating space habitat, the centripetal acceleration is due to the rotation and can be equated to the gravitational acceleration (g).

The formula to calculate centripetal acceleration is given by:
ac = (v^2) / r

Where:
ac = Centripetal acceleration
v = Linear velocity of the object
r = Radius of the circular path

Since the variation in g between the head and feet should be less than 1/100 g (0.01 g), we can express it as:
Δg = g - g_head = g - g_feet < 0.01 g

Now, we can equate the centripetal acceleration (ac) to the difference in gravitational acceleration (Δg):
ac = Δg

Substituting the formula for centripetal acceleration, we get:
(v^2) / r = Δg

Assuming the linear velocity (v) is constant throughout the space habitat, we can ignore it for the purpose of this calculation.

Now, we rearrange the equation to solve for the minimum radius (r):
r = (v^2) / Δg

Since we want to find the minimum radius relative to one's height, we can replace the linear velocity (v) with the circumference of a circle (2πr) and the radius (r) with the height (h) of the person.

Therefore, the equation becomes:
h = (2πr^2) / Δg

Solving for the minimum radius (r), we rearrange the equation as follows:
r^2 = (Δg * h) / (2π)

Finally, taking the square root of both sides, we find:
r = √((Δg * h) / (2π))

Using this formula, we can calculate the minimum radius required for the space habitat given the height (h) and the desired variation in gravitational acceleration (Δg).