[jerrygg38 (OP)]

Ok so we can define gravitation as a system with no centrifugal force. Any others?

I don't think you get it.

The great theory of Newton on gravity is that what holds the planets in orbit is the force of gravity acting on them directing them towards, roughly, the sun.

Centrifugal force is the force supposedly directed outwards away from the center due to rotation. This is, in all cases, due to the equal and opposite reaction of being diverted towards a center from otherwise linear motion.

  The equal and opposite reaction may be true but what does it mean? Centrifugal force is equal and opposite to centripetal force is something we can memorize but it lacks meaning. What is the mechanism by which it is true? The basic understanding of physics is lacking. All we have are rules to remember. And I for one want to know why!

[hamdani yusuf]

Ok so we can define gravitation as a system with no centrifugal force. Any others?

I don't think you get it.

The great theory of Newton on gravity is that what holds the planets in orbit is the force of gravity acting on them directing them towards, roughly, the sun.

Centrifugal force is the force supposedly directed outwards away from the center due to rotation. This is, in all cases, due to the equal and opposite reaction of being diverted towards a center from otherwise linear motion.

  The equal and opposite reaction may be true but what does it mean? Centrifugal force is equal and opposite to centripetal force is something we can memorize but it lacks meaning. What is the mechanism by which it is true? The basic understanding of physics is lacking. All we have are rules to remember. And I for one want to know why!

Centrifugal force emerges when there are strength difference in centripetal forces working on parts of a system.
In a turning moving car, the road forces the wheels sideway which in turn forces other parts of the car which is then felt by the passengers. The passengers don't receive any force directly from the road.
In ISS, the earth forces each part almost equally, including every atoms of its passengers. That's why they don't feel the centrifugal force even though centripetal force done by the earth to them through gravity is comparable to the turning car.

[PmbPhy]

What is centrifugal force?

Simply put, centrifugal force is an inertial force. If you're at rest in a rotating frame of reference then objects which are moving with no acceleration in the inertial frame will accelerate in your frame.

You can read more about inertial forces on my website at:
http://www.newenglandphysics.org/physics_world/gr/inertial_force.htm

[jerrygg38 (OP)]

hamdani yusuf said:
In ISS, the earth forces each part almost equally, including every atoms of its passengers. That's why they don't feel the centrifugal force even though centripetal force done by the earth to them through gravity is comparable to the turning car.
You raise an interesting point. Why don't we feel the rotation of the Earth? You say that everything upon the earth has equal forces on it. In other words, you need differential forces to feel the centrifugal force.
Thus the Earth itself has a centrifugal force relative to the sun. It may be that our atmosphere acts a counterbalance to our centrifugal forces. If the Earth spun faster and faster each second, then perhaps we would notice this force.
   In the space station, they are moving fast but they do not experience being pushed against the outer side of the cabin. Thus again they are subject to the same force as the space station but they are inside the station. So they feel nothing. The space station as a whole feels the centrifugal force.
 

[jerrygg38 (OP)]

To all:
  It seems to me at the moment that centrifugal force is similar to the force that occurs when you try to rotate a gyroscope slightly perpendicular to its axis. It is beginning to seem to me that it is not a fancy space time force but a simple internal force that originates within the object itself. Any other ideas from the world of science?

[hamdani yusuf]

We don't feel earth rotation because it is too slow for our senses.

[alancalverd]

Why don't we feel the rotation of the Earth?

We do.

Because of a planet's rotation around its own axis, the [net] gravitational acceleration is less at the equator than at the poles. In the 17th century, following the invention of the pendulum clock, French scientists found that clocks sent to French Guiana, on the northern coast of South America, ran slower than their exact counterparts in Paris.

[jerrygg38 (OP)]

Why don't we feel the rotation of the Earth?

We do.

Because of a planet's rotation around its own axis, the [net] gravitational acceleration is less at the equator than at the poles. In the 17th century, following the invention of the pendulum clock, French scientists found that clocks sent to French Guiana, on the northern coast of South America, ran slower than their exact counterparts in Paris.

  The force is MV^2/R where the rotational velocity is around 1000 miles per hour and the distance to the center of the Earth is around 4000 miles. So I guess this is small.
  As far as the gravitational acceleration on different points of the Earth, the programmers of my 5 inch gun system took this into account as the various forces operating upon the Earth had to be accounted for to insure accuracy. I was the hardware designer but the physicists and programmers took so many things into account including air pressure.

[rmolnav]

SOME of you base your arguments on the idea that c. f. is not actually real.
Last year I defended the opposite, in more than one "subject", particularly in the one relative to the existence of 4 high tides a day, instead of just 2.
I did it gaving many examples. Now just a very simple one:
Imagine you are rotating a weight, with the help of your hand (and wrist) and a string. Somebody has already put this case.
Let us put a dynamometer between weight and string. It will show the centripetal f. that is producing the rotational movement (the dynamometer pulling the weight).
But the ACTION AND REACTION principle says that if that mentioned force exist,  the weight is also pulling the dynamometer with another opposite and equal force. That is a REAL force, and CENTRIFUGAL.
By the way, the same could be said in relation with the knot between the string and the dynamometer ... And this instrument functions with two opposite forces applied at its extremes. At the inner one it would be the centripetal force (the string pulls inwards the dynamometer ), and at the outer one the centripetal force (the weight pulls outwards the dynamometer)

[rmolnav]

#28 (continuation)
Sorry I erroneously said "4 high tides a day, instead of just 2". Logically it should be 2 instead of 1.
Perhaps I was thinking in the fact that, being tides produced mainly by Moon, but also by Sun, there are actually 2 high tide bulges due to Moon, and 2 due to Sun. But both tidal effects are seen added, and the result is just 2 high tides syncronized to Moon position. The Sun tide result is the oscillation in tidal coefficient, according to Sun/Moon relative position.

[hamdani yusuf]

Imagine a weight floating in space far away from anything else. Let us put a dynamometer between the weight and a string.
If the string is pulled the dynamometer will register a value, which is indicating that opposing forces are acting on its ends.
The question is, what force is acting on the dynamometer from the weight's side?

[rmolnav]

#30
The string pull would produce an acceleration of both dynamometer and weight. After some transient situation, if somehow the string pull keeps constant, the acceleration of the weight would continue. That means the dynamometer is pulling the weight, and due to action and reaction principle the weight would also be pulling the weight, with equal but opposite force.
By the way, the force shown by the dynamometer would be not only the mass of the weight times the acceleration ... The mass of the dynamometer times the acceleration should be added.

[rmolnav]

#24
Not bad idea. Those orce and torque are reactions to others that are trying to change movements that, due to the inertia of objects, without any force/torque would keep with a kind of constant movement.
In one case the movement "tries" to maintain its velocity vector (value and straight line of movement), and the gyroscope tries to keep constant its angular momentum vector (value of angular speed and direction, both of vector and perpendicular planes of movement of all parts of the gyroscope) 

[hamdani yusuf]

Newton's laws of motion are three physical laws that, together, laid the foundation for classical mechanics. They describe the relationship between a body and the forces acting upon it, and its motion in response to those forces. They have been expressed in several different ways, over nearly three centuries,[1] and can be summarised as follows.

First law: In an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a net force.[2][3]
Second law: In an inertial reference frame, the sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration a of the object: F = ma.
Third law: When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.

According to Newton's Law, something is called force if it can produce acceleration. If mass is considerably constant, force is what is needed to change an object's velocity.

In linear acceleration like my example above, the dynamometer reads a value because the weight has inertia which then produce reactional force. It doesn't accelerate the weight to the opposite direction of the pull on the string, i.e. if the pull is stopped, the weight won't reverse the acceleration.
The analogy is applicable for angular acceleration, which requires a centripetal force. The centrifugal force is merely reactional, due to the inertia of the weight. If the centripetal force is stopped, the weight won't accelerate away from the center of the rotation, but merely continue with the latest velocity.

[rmolnav]

#33
Thank you for putting it that clear. Just a short comment, mainly aimed to others.
You say:
"If the centripetal force is stopped, the weight won't accelerate away from the center of the rotation, but merely continue with the latest velocity".
Right, but that doesn´t mean, as others say, that centrifugal force doesn´t exist, that it is only kind of sensation due the "natural" tendency of the rotating object to follow the tangent ...
As long as the centripetal force "starts", the object otherwise moving in a straight line, suffers ONLY that force, and consequently a centripetal acceleration that makes it rotate. The centrifugal one is the reaction exerted ON THE STRING (or the dynamometer if installed) by the weight.
Should the string brake, logically both centripetal force and its reaction (centrifugal) suddenly go to null. The previously rotating objects follows the tangent (dynamometer included if braking point is more inside), and the string falls down due to its own weight. Weights of considered objects have not being considered, supposing that are rather negligible compared to other acting forces. It only would mean that the string would shape a short cone instead of a perfect circle, but this doesn´t change our arguments.   

[puppypower]

Is the centrifugal force active in all rotations, from electron to galaxy rotation?

[rmolnav]

#35
Yesterday I sent a reply, but it is not here! I don´t know why ...
Not being English my mother tong, it takes me long time to write them! Ill try to repeat it, perhaps rather shorter.
Newton mechanics finds problems at atomic scale (quantum physics should "theoretically" be applied), and at galaxies, where the supposed existence of black holes and dark matter makes the issue very difficult to grasp.
But similarly to the couple Earth/Moon, and Sun/Earth, all satellites rotating around planets, and all planets rotating around stars, don´t move following a straight line thanks to the gravitational pull between them.
When one of the celestial objects is very massive compared to the other, this is the one which is considered to be rotating, and the pull from the other is normally called centripetal. Its reaction, the small one pulling the much bigger, could arguably be called "centrifugal", because its sense is "outward".
What actually happens is that both objects rotate around and axis at their barycenter, usually less than a radio away from the bigger object center.
That is perceived as a wobbling of this last object.

[rmolnav]

#36 (continuation)
I said:
"... Its reaction, the small one pulling the much bigger, could arguably be called "centrifugal", because its sense is "outward".
We should keep in mind that use of the term "centrifugal" is not the unique possible one. When dealing with massive objects frequently, for the sake of simplification, their masses are considered to be at their centers of gravity. But they are the addition of huge amounts of particles, that don´t normally experience same forces, equal to the ones in the simplified case of all mass at gravity center.
That fact allows the existence of many, many other pairs of centripetal/centrifugal forces.
Perhaps it would be easier to understand what I mean reading now what I said last year in a post at the subject relative to the existence of two high tides a day instead of one:
"Imaging just a steel cylindrical bar hanging from one of its ends. If we made a horizontal cut, the lower part would fall down. Why it didn´t fall before? Because of internal tensile stresses: the upper side of the section was pulling the lower one, exactly with a force equal to the weight of lower part of the bar.
If we had made the cut a little lower, we could say the same. In this case the weight of lower part would be a little less: just the weight of the slice between the two cuts.
As the slice is not experiencing any acceleration, the sum of all forces applied to is null. The sum of internal stresses it suffers from contiguous material, plus its own weight, has to be null.
If we produced any upward acceleration to the hanging point, internal stresses would increase in such a way that the sum of weight of the slice plus stresses from contiguous material would give a net force that divided by slice mass would be equal to the acceleration"

[hamdani yusuf]

According to Newton, a force is required to make an object accelerating. A rotated object by a string is accelerating (towards the center of rotation), hence there must be non-zero force working here, which is centripetal force.
That's why many people don't consider centrifugal force as a real force, at least in Newtonian sense. Because if we include the centrifugal force to the equation of the system, total force would be zero which mean no acceleration, contrary to the observation.

[jeffreyH]

Acceleration is a strange beast with two components, direction and magnitude. An unchanging magnitude may well cancel centrifugal and centripetal forces. As in an idealised perfectly circular planetary orbit. Though not in an elliptical orbit.