# Rotation Problem: Earth lengths/Apparent Weights

• a Vortex
In summary, a friendly Brazilian with a mass of 150 kg rotates in a circle around the center of the Earth once per day with a radius of 6.40 x 10^6 m. The normal force experienced by the Brazilian is 1.4649 x 10^3. The question is how long a day would have to be for the Brazilian's apparent weight to be 1.46 x 10^3 N, and the answer is about 6.16 x 10^4 sec or 17.1 hours. The weight is equal to the normal force.
a Vortex

## Homework Statement

A friendly Brazilian has a mass of 150 kg. Being in Brazil, he rotates in a circle around the center of the Earth once per day, The radius of this circle (which is essentially the radius of the Earth) is 6.40 x 10^6 m.

I have found that the normal force is 1.4649 x 10^3.

## Homework Equations

ac = v2/r , centripetal acceleration
$\Sigma$F=ma
v = (2$\pi$r)/T , T is period of one revolution

## The Attempt at a Solution

I only got to mg - Fn = mac
I know what the apparent weight is but I'm not sure about the normal force. If I can find this, then I can then find ac, v, and then T to find about the length of day.

What is the question?

ehild

Sorry forgive me. The question is: How long would a day have to be for the Brazilian's apparent weight to be 1.46 x 10^3 N?

Btw, the answer should be about 6.16 x 10^4 sec or 17.1 hours.

The weight is equal to the force the man presses a horizontal support - scales, ground, chair ... So its is the same as the normal force.

ehild

Your calculations so far are correct. The normal force, Fn, is the force that the ground exerts on the person to balance out the force of gravity, mg. In this case, the centripetal force (mac) is also acting on the person, causing them to rotate around the Earth. Therefore, the normal force must also equal the sum of the person's weight (mg) and the centripetal force (mac).

To find the length of a day, you can use the equation T = 2πr/v, where T is the period of one revolution, r is the radius of the circle (in this case, the radius of the Earth), and v is the velocity. Since the person is rotating once per day, the period is 24 hours or 86400 seconds. You can use this value for T and solve for v, which will give you the velocity at which the person is rotating around the Earth.

Once you have the velocity, you can use the equation ac = v^2/r to find the centripetal acceleration. This will also give you the value for the normal force, which you have already calculated. From there, you can continue with your calculations to find the length of a day.

It is important to note that this calculation is assuming that the person is rotating on the surface of the Earth, which is not exactly true. The Earth's rotation is not a perfect circle and the person's rotation would also be affected by the Earth's tilt and other factors. However, this calculation provides a good estimate for the length of a day on Earth.

## 1. What is the rotation problem?

The rotation problem refers to the phenomenon where objects at the equator experience a different weight than those at the poles due to the Earth's rotation. This is because the centrifugal force caused by the rotation of the Earth is greater at the equator than at the poles.

## 2. How does the Earth's rotation affect the length of a day?

The Earth's rotation is responsible for the length of a day. It takes the Earth approximately 24 hours to complete one rotation on its axis, which is what determines the length of a day. However, the Earth's rotation is gradually slowing down, causing days to become slightly longer over time.

## 3. What is the Coriolis effect and how does it relate to the rotation problem?

The Coriolis effect is the deflection of objects or fluids moving on the Earth's surface due to its rotation. This effect plays a role in the rotation problem as it contributes to the differences in apparent weights and lengths experienced at different latitudes on Earth.

## 4. How does the rotation problem impact travel and navigation?

The rotation problem has minimal impact on ground travel and navigation as it only causes slight variations in weight and length. However, it is a crucial consideration for air and sea travel as it affects the movement of aircraft and water currents.

## 5. Can the rotation problem be solved?

The rotation problem is a natural phenomenon caused by the Earth's rotation and cannot be "solved" per se. However, it is well understood by scientists and its effects can be accounted for in various fields such as physics, geography, and meteorology.

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