I am simply amazed at the lengths this person has gone to defend and justify his odd worldview. If only that energy had been spent trying to understand actual physics, and why physicists consider centrifugal force imaginary.

http://www.physicsnews1.com/question_5.html

I'm just astounded by this site and his writings. He has such a large body of written work up there, and a not-terrible google page ranking (which I just helped, ppt), and yet he appears to be very confused. This is why I tend not to trust sites that don't have a 'comments' section.

He appears to be completely confused as to what 'centrifugal force' is. This is a poor definition, but its short and I think sufficient for this:



The main point here, in the context of this guy's ramblings, is that this is an imaginary force acting on the rotating body (not on anything else), and that (within the rotating frame) it acts to balance the centripetal force.

Within the reference frame of the rotating body (say a rock tied to a string which you swing above your head), the rock neither moves inwards nor outwards, though there is a definite force inwards (applied by the string). In any static situation, if an inward force is applied and the rock doesn't move inward, there must be an outward force balancing it. In the rotating frame, the rock behaves as if all the forces were balanced. Thus there is an apparent force outward acting on the rock - a fictional force.

A key fact that he is missing in this 'analysis' is: the revolving body is being accelerated towards the center. Sure, it doesn't move towards the center, and its speed is constant, but its velocity is always changing (since the direction of movement is always changing). (Acceleration is a change in velocity, regardless of whether speed is changing.) This is completely unlike a static situation, where an inward force must be balanced by an outward force. Here, there is a net force (inward) and a net change in acceleration, and the 'outward' force acting on the rock does not exist.

In his criticism, he appears to confuse 'centrifugal force' - which is an imaginary force 'applied' (so to speak) to the rock - with the real force which the string applies to your hand. I think he is correct that the string applies a real outward force to the hand in opposition to the real inwards force applied to the rock; that just has nothing to do with the existence of an imaginary centrifugal force applied to the rock.

This is really interesting to me, I had no idea that there is so much debate on this topic online. The guy I linked to above still strikes me as completely confused, but there are far more intelligent and informed people who are debate whether 'centrifugal force is imaginary'

As far as I can tell, it reduces to two semantic issues:

1) Can we call it imaginary when its real within the rotating frame?

and

2) Can we call any force that acts in the centrifugal direction a centrifugal force?

Setting aside those semantic arguments, no sensible person seems to argue that the tendency of the object to pull against the string is NOT due to a real force within the non-rotating frame.


Here is a link to another 'centrifugal force is real' which is a bit more focused:

http://blogs.discovermagazine.com/badastronomy/2006/08/30/when-i-say-centrifugal-i-mean-centrifugal/


His point seems to be "centrifugal force is real enough within the rotating frame", and I agree, but its precisely because it only behaves that way within the rotating frame that we term it 'imaginary' (or pseudo or fictional).

A dozen or so tools chime in simply to 'agree', before people really start to discuss it. I liked this post:

Groan. You can fully mathematically define vectors and angular momentum in the time it takes to read his article.

However, just because the engine supplies the torque, the spinning wheels are not invisible.

They are kind of blurry.

Exactly! If he had spent that time listening to you explain vectors and angular momentum rather than writing his massive set of 'articles', the world may be a better place.

And I'm sorry if anyone had their life sucked out of them by following the link I posted...I was so itching to comment on his site (but unable) that I scratched that itch by commenting here.



(I think I may have missed something).

A thought experiment.

Compare two men inside a twelve foot diameter heavy equipment tire.

In case one the man runs along the inside of the tire matching speed exactly with the equipment running (rolling) down the road. Each time the man's foot hits the top of the inside bottom of the tire, the tire is touching the road so has zero net velocity at that point. The man's foot in contact with the tire provides his ability to run and keep pace with the vehicle. Of course the Top of the tire is going at twice the man's velocity for the vectors to all zero sum.

In case two the other man is simply laying in the bottom of the tire and if the forward speed is sufficient, the centrifugal force will keep him pinned to the inside of the tire as it spins.

To make this short, the running man is doing his own work and is an independent system although both examples are equal mass moving at equal velocity acting inside the system of the wheel.

The second man is doing no work so the dw/dt equation will collapse while leaving the F=MA equation intact.

Just like a piece of gravel on Earth being accelerated through space but held in place by gravity, the small rock does no work.

It is work that makes the forces "real".

However the motion and "appearance" of work blurs the difference.

The thought experiment with the two men inside the 12-foot diametre tire did not work out. It had some repeatability problems. The men died of asphyxiation before they reached a constant speed. The scientists were tried for second-degree murder, and they were hanged.

The running man works only because he is accelerating and decelerating his legs and feet, without which motion he could not stay on the bottom part of the tire. But his work is entirely due to the nature of a human's locomotion.

If you put a ball inside the tire, the ball will eventually roll along at the top surface of the bottom part of the tire which is in contact with the ground. The ball will never lift off, it will not exert work, because once its kinetic state comes to an equilibrium, that is, rolling around its horizontal axis at a constant rate, and moving ahead in the same direction and speed as the axel of the truck or the axis of the rotating tire in which it is in, then its motion will be maintained by the constantness of its velocity, which requires no work, according to one of Newton's laws, that is, 'a body at rest or moving at a steady pace in an unchanging direction will not require any work or energy to continue with its progress'.

I couldn't quite follow that.

Another way to look at it is simply by vector math. Centrifugal force is just the reaction of the angular acceleration of a body moving in a constant velocity with a non constant direction. The force needed to change the direction is what we call centrifugal force. The force is real but only because you are becoming part of another system. I doesn't exist separately. The man running in the tire is a separate system providing his own motion. The man laying in the tire and spinning around has become part of the tire, just like any other part. The both get to the same place at the same time but only one experiences "centrifugal forces".



In one context centrifugal forces are very real in that they are used do specific jobs. The change in angular momentum of a spinning glass vile is how blood is separated into plasma and how third world countries separate U-238 from U-235 to make atomic bombs.

Reactions are forces caused by other forces. To make a static example without the use of angular momentum, you could tie a rocket to the ground and measure the force on the ropes which kept the rocket from flying away. The tension on the ropes would exactly counter the thrust of the rocket (in vector math)... or the ropes would break. The reaction forces on the stakes holding the ropes to the ground would exact equal the forces on the ropes also but exist only as reactions. They have no ability to do work independently. If they move and are allowed to do work, the system expands until the laws of statics are fulfilled and the vectors sum to zero or to the force vector of acceleration. F=MA always rules.

The usual example of the vector math for centrifugal force is the carnival ride where you have a large ring holding up baskets supported by cables. As the ride rotates the baskets swing outward. If the angle of outward swing is 45 degrees then the vertical force vector (gravity) is equal to the horizontal force vector (centrifugal force). If the cable breaks the basket and it's unhappy occupants travel through space at whatever velocity they had at that moment with no change in angular momentum.

Gravity is not their friend.

Actually the math isn't that hard. Regardless if you consider the force imaginary or an actual angular acceleration, the units are those of acceleration such as feet/second squared.

Consider the moon with a period of 27.3 days. Assume the orbit is circular with a radius of 239,000 miles. The magnitude of the acceleration towards the Earth (centripetal acceleration)would be...

239,000 miles = 3.85 x 10**8 meters. T (period) is 27.3 days = 2.36 x 10**6 seconds.

v=2(pi)r/T = 1020 meters/sec

The centripetal acceleration is

A = v squared/r = 1020/3.85x10**8 = 0.00272meter/sec**2

I haven't yet invested the time to understand what you are saying, MetalWing, but I do want to chime in and (setting semantics aside) agree emphatically with this statement:



"That which is called centrifugal force" is a very real phenomena with very real consequences. Its just that its not really a true 'force' per se. This doesn't make the phenomena any less real, or important.

Please then, define "a true force."


My washing machine utilizes this to wring out my clothes.
Isn't this simply momentum traveling in a circle?

If we go back to the satellite example traveling in orbit. The only true force is the acceleration of gravity.

In your washing machine the only true force is your electric motor. The rest are force vectors and resultant forces that are extensions of the motor and help the motor do the work. The motor spins your clothes dry, not centripetal force.

Still, how would you actually define the meaning of "a true force."

Do you really understand gravity? If you do, then you are even ahead of scientists.

Lots of well known attributes of gravity.

Its how gravity fits into a pre-broken symmetry that is unknown, its how gravity interacts at the quantum level that is unknown.

Specifics, specifics.

I know that gravity is having a terrible effect on my breasts.

It's probably the centripetal effects!

The modifier 'true' is only being used to discriminate actual forces from apparent influences that appear to act like forces within limited points of view. Thats the only purpose of the word 'true' here - so be 'truy force' I really mean 'force'.

From wikipedia:



The rock-on-a-string-spun-in-a-circle does not have any outward influence causing it to accelerate outward, so it has no true force acting outward. It does have a true force acting inwards (by the string). If you are an ant riding the inside surface of that rock, you will feel like you are pressed against it because, as you correctly say...



...your momentum causes you to push against the rock, as the inward surface of the rock provides a real inward acting force which accelerates you. It doesn't change your speed, it changes the direction of your velocity.





I think my use of the word 'true' has caused confusion here, I hope my comments above have addressed this. We don't have to 'truly understand' gravity in order to differentiate between an influence which causes a real acceleration, and an influence which only appears to cause an acceleration within a limited viewpoint.



Exactly.