Centrifugal force acts on a fixed object that is being rotated on an axis. It is the force that drives the object away from the axis or center of rotation. In science, it is described as a fictitious force, one that is not naturally present.
Experiencing centrifugal force
One of the most brilliant examples of how centrifugal force is created and what effect it has can be found on carnival rides in amusement parks. They operate under different trade names, but the most common one is the Gravitron. It is a circular drum rotating around an axis.
The thrill seekers, aka passengers, enter the drum and are distributed evenly into individual compartments where they stand with their backs to the outside wall of the drum, facing the center axis. Once all the passengers are in place, the entry door is closed and the operator starts the thrill ride.
Once rotation commences, it reaches its maximum rotational speed in less than half a minute, creating up to 4 G of centrifugal force on the riders, pinning them to the wall. At about 25 rotations per minute, the Gravitron reaches its maximum speed, and to the occupants it will seem like the bottom has fallen out. As the drum is raised, the centrifugal force holds the passengers firmly against the wall.
According to Newton's Third Law:
"Actioni contrariam semper et aqualem esse reactionem: sive corporum duorum actiones in se mutuo semper esse aquales et in partes contrarias dirigi."
"To every action there is always an equal and opposite reaction: or the forces of two bodies on each other are always equal and are directed in opposite directions."
This is something learned in early natural science classes. One of the consequences of this law is that a very large person exerts a very large force on the outer wall of the Gravitron, whereas a lightweight person's force is less. The force is directly proportional to the person's weight.
Another way to observe centrifugal force would be to take a bucket of water and attach it to a similar device as the Gravitron: As it accelerates, the contents of the bucket are held in place by the centrifugal force, and one may spin the bucket in any direction including upside down, without spilling a drop, provided that is has a high enough rate of rotation.
Essentially centrifugal forces take over when the force applied exceeds 1 G, which is the standard used for the force of gravity. 1 G equals the earth's gravity, or the amount of force necessary to lift any given object off the ground.
Centrifugal force and artificial gravity
In human physiology, gravity is very important to maintain bone mass. Newton and his contemporaries could have never envisioned that centrifugal force might eventually be used to create artificial gravity in spacecraft orbiting the earth or reaching deep space. It would maintain a semblance of normalcy for the occupants of a device reaching for frontiers unknown to humankind. It will be of relative importance, when future explorers head for other planets, that they be able to move about normally.
Observations were made early on in space flight showing that extended exposure to weightlessness could lead to loss of muscle and bone mass. While the muscles will regenerate, it is thought that the effects on the human skeleton are permanent and irreversible.
By applying a slow rotation to a spacecraft, artificial gravity can be induced, as Newton's Third Law is equally valid in zero gravity as it is here on earth.