# Centrifugal force in Rendezvous with Rama

• itchybrain
In summary, the book "Rendezvous with Rama" by Arthur C Clarke features a large cylinder rotating at high speeds. Inside the cylinder, there is no gravitational pull along the long axis, but there is a pull felt along the inside shell. This is due to the passengers' inertia against the rotating shell, simulating a centrifugal force. The atmosphere of Rama also rotates with the cylinder, causing variations in the perceived gravitational force depending on altitude and speed. If the atmosphere were evacuated, there would be no pull felt when traveling perpendicular to the axis, but there would be a constant force required to maintain altitude when traveling from the side towards the central axis. The force exerted on a biking astronaut is caused by the curved path they
itchybrain
SPOILER ALERT: This question will refer to, and may have spoilers, regarding Arthur C Clarke's Rendezvous with Rama. Read below at your own peril.

BTW the book is totally worth reading.

In the book, the astronauts basically encounter an immensely large cylinder, rotating along its long axis at high speeds. Once inside, they describe how along the long axis ("center of the cylinder") there is no sense of gravitational pull, but along the inside shell of the cylinder, a pull is felt.

I believe I understand the concept here. Any force that will "pull" someone "down" (or into the ground) can be compared to a gravitational force. In this particular case, Rama does not distort spacetime and does not create gravitational forces, but the passenger's inertia against the rotation shell simulates gravitation (centrifugal force, though some object to this term).

Now, Rama has an atmosphere. In another part of the book, one of the astronauts "bikes" with a flying bike from one axis to another, and experiences gravitational force of different intensity, depending on the height of the flying trajectory (perpendicular distance from the rotating shell, alternatively the perpendicular distance from the axis). If traveling along the axis, no pull whatsoever is felt.

What is exerting the force on this biking astronaut? Is it Rama's atmosphere? The astronaut, when flying/biking, does not have any contact with the spinning shell.

In other terms, if Rama's atmosphere was evacuated, and one decided to push themselves from one end-axis to the other, would they fell a pull as well if they deviated from the main central axis?

dkotschessaa
I realize you read this in a book, but it is a real physics question, so I'm moving it to "classical physics".

We do also get this question occasionally, but typically referencing climbing a ladder "up" toward the central axis. The answer is the same though, either way (and yes, it is in Greg's link):

First, it is important to understand what the atmosphere is doing. It is rotating with the cylinder and since the cylinder is fairly small, the mass of the air doesn't impact its pressure much (pressure is constant everywhere). So as you go "up", you continue rotating with the atmosphere, but at a decreasing linear speed and therefore against a decreasing "gravitational" force. Traveling along the axis is easy and fun this way, but you must be careful when traveling perpendicular to the axis because your motion will substantially impact the "gravitational" force you feel. Specifically, when you fly along the axis, the lift you require/gravity you feel depends only on your altitude, not your speed. But when you fly perpendicular to the axis, the lift you require/gravity you feel also depends on your speed.

 Oops: I didn't actually answer the question. I described what is felt, but not what causes it. What causes the felt force is the curved path the person must take to maintain his course. It may not look like it to him, but he's actually flying in circles.

The last question is harder and depends on exactly how he achieves the course. If he starts from the side and lifts "up" toward the central axis, he will need a constant force to maintain his altitude because he's still rotating with the cylinder (flying with a circle). But if he starts from the central axis, he's just rotating in place and will not require any forces to maintain linear motion toward the other end of the cylinder once he starts moving.

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dkotschessaa
itchybrain said:
What is exerting the force on this biking astronaut?
What force exactly, and how is that force measured?

itchybrain said:
Is it Rama's atmosphere?
If the flying bikes use aerodynamic surfaces, propellers etc. then there will be forces by the air on the bike.

itchybrain said:
In other terms, if Rama's atmosphere was evacuated, and one decided to push themselves from one end-axis to the other, would they fell a pull as well if they deviated from the main central axis?
No, when in free fall you don’t feel any pull. This is also true for gravity caused by a mass. But your trajectory can still look accelerated from the rotating frame.

Look up "proper acceleration" (feeling a force) vs. "coordinate acceleration" (changing velocity in some frame of reference).

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I know this is a two year old thread, but I wanted to thank the contributors. I am reading this book and had the exact same questions.

russ_watters

## 1. What is centrifugal force in "Rendezvous with Rama"?

Centrifugal force is a fictitious force that appears in the book "Rendezvous with Rama" by Arthur C. Clarke. It is the outward force experienced by objects in a rotating frame of reference, such as a rotating space station.

## 2. How does centrifugal force play a role in the book's plot?

In "Rendezvous with Rama", the centrifugal force created by the rotation of the mysterious cylindrical object, Rama, is used to simulate gravity for the human explorers inside. This allows them to move around and conduct their research as if they were on a planet with gravity.

## 3. Is centrifugal force a real force or just a concept?

Centrifugal force is a concept, not a real force. It is a result of an object's inertia, or tendency to resist changes in its motion, in a rotating frame of reference. In reality, it is the centripetal force, or the force that keeps objects in circular motion, that is responsible for the outward "force" experienced as centrifugal force.

## 4. Can centrifugal force be used for space travel like in the book?

While centrifugal force can simulate gravity in a rotating space station, it cannot be used for space travel. In order to maintain the same level of artificial gravity, the space station would need to rotate constantly, making it difficult to navigate and control. It is more practical to use other means of propulsion for space travel.

## 5. Are there any real-life examples of centrifugal force in use?

Yes, there are several real-life examples of centrifugal force in use. Some examples include centrifuges used in laboratories to separate substances by density, amusement park rides that spin around a central axis, and the circular motion of planets and moons around larger celestial bodies.

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