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Anonymous Poster

Forces of Nature

03/14/2007 11:13 PM

You are demonstarting different "forces of nature" to class of very interested students. You tie a string to a steel bucket handle (center top) and fill the bucket half full of water. You then start swinging the bucket around in a circle over your head....Hold your thoughts group this is not that obvious. A student ask you "what force will you need to GIVE up to cause the water to leave the bucket?

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#1

Re: Forces of Nature

03/15/2007 12:18 AM

i know the answer to this! It's at the tip of my tongue!!!!!!!!

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#2

Re: Forces of Nature

03/15/2007 7:19 AM

I don't know if I understanded well the question, but there are some options.

1. Pressurize the water from the bottom of the bucket, make it explode from inside it out. Force = pressure x area

2. Loose the string. The bucket flies, the water goes out. Force = string pull

3. Release the bottom of the bucket. The water goes out. Force = resulting from the water pressure under centripetal acceleration x area of the bottom of the bucket.

And finally, if the bucket is at rest and you'll turn it to make the water goes out, you're just making sure that there's nothing impeding the gravity of doing it's job.

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#3

Re: Forces of Nature

03/16/2007 2:09 AM

If you give up half the force holding back the bucket (controlled slip of the string) or give up all the force (release the string) most of the water will stay in the bucket until it is stopped by a collision.

The solution might be to have one of the students use his head (force of positive thinking) to stop the bucket and create the spill.

New bucket law : The speed of the bucket is directly proportional to the amount of pain.

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#4

Re: Forces of Nature

03/16/2007 3:53 AM

tenseness of the string divided by the average stickiness of the fingers equals the square of the altitude of the bucket, assuming the velocity of the water at rest is zero and that all the mute sweating observers are thirsty, OR (according to the recent work of Frownovitz et al.) as the velocity of the bucket nears the speed of light and the half full bucket of water "decides" to become half empty just as my turn to drink from it is next in line... the relativistic forces involved will trick the by now dehydrated and desperate observers into thinking their mouth is NOT now shifted over to a position just under the left ear when it actually is, and all the water thus spills out onto the ground.

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#5

Re: Forces of Nature

03/16/2007 4:52 AM

There are four fundamental forces in the universe, the strong nucleic force, the weak nucleic force, the electromagnetic force and gravity.

So the question is which one of these is the force that is opposing the centripetal acceleration caused by the rotation of the bucket.

My money is on the ELECTROMAGNETIC FORCE.

The reasoning behind this is, the string is made up of chemical compounds, that are, in turn, constructed from atoms. The atoms are bonded together in chemical reactions, which involve the movement of electrons, causing charge imbalances, between the atoms, and bonding them together. Since it is an electric charge, that is holding the molecules the string is made of, together, then the removal of the electro magnetic force would result in the failure of the string. If the string fails then the bucket would no longer be restrained.

So there you have it, take the electromagnetic force away and the string breaks. Mind you the bucket, handle and everything else, including you, breaks as well, so it would be a really messy and nasty experiment.

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#9
In reply to #5

Re: Forces of Nature

03/16/2007 8:11 AM

But, why would the water then (and at the same time) leave the bucket? If the sting broke, would not the water simply follow the bucket? Inside the bucket? Since the force keeping the water in the bucket is equally counteracted by gravity--the force imparted by the bucket's orbit about the hand is just sufficent to hold the water from falling--then would not gravity be the force required to keep the water in the bucket? Hence, lose gravity--lose the water?

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#10
In reply to #9

Re: Forces of Nature

03/16/2007 9:03 AM

"But, why would the water then (and at the same time) leave the bucket?"

Remember the bucket, handle string and everything else that has a chemical bond in it would cease to stay as is and would break down into it constituent atoms. That includes the water in the bucket turning into hydrogen and oxygen.

"Since the force keeping the water in the bucket is equally counteracted by gravity--the force imparted by the bucket's orbit about the hand is just sufficent to hold the water from falling--then would not gravity be the force required to keep the water in the bucket? Hence, lose gravity--lose the water?"

If you carried out the experiment in a zero gravity environment the water would stay in the bucket. There is a continuous force being applied to the bucket by the string, which is causing the bucket to continually change direction, forming the circular path. The bucket is in turn applying a force to the water, keeping the whole assembly contained. Yes the bucket and water would sail off into the never never, but only until it impacted something, at which time the water will spill. So in reality gravity has nothing to do with containing the water and if removed from the equation, would not upset the system. That leave the nucleic forces and electromagnetic force and sine we are not playing around with the nucleus of an atom that only leave the electromagnetic force.

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#27
In reply to #10

Re: Forces of Nature

03/19/2007 5:16 AM

Thank you for a fine, and concise explanation. Reconsidering, it occurs to me that I was taking a more restricted, a more minimalist point of view...mostly owing to what the OP puzzle seemed to be suggesting--to me at least--namely: that the bucket started out dangling from the string held on the earth's surface, from which it was to be swung upward ("overhead") and, thence, in an ever-repeating circle which was vertical with respect to (presumably) the earth's gravitational center. Given such a frame of reference as the puzzle's wording was suggesting to me--also one in which even the act of swinging a bucket in a specified direction could be accomplished with much less difficulty than (shall we say) trying to commence slinging a bucket in a circle in a frame of reference in which there is no direction--no up/overhead or down--and no convenient means by which the swinger himself (holding only the string) might impel the bucket--might get the bucket started moving circularly--without also impelling himself, it occurred to me that the solution wanting should involve a force necessary to contain water inside and at the bottom of the bucket at the outset; not the force necessary for the water, string, or bucket even to have form in which the centripetal and centrifugal phenomena could be given effect. Your view of the puzzle, on the other hand, seems to introduce a special case: one in which the direction, up, is with reference--somewhat arbitrarily it might seem--to the person holding the string--where up is defined by the orientation of the swinger's head; and in which more is involved than just maintaining or not maintaining the water in the bucket. And, if we could surmise that the electromagnetic force ceased to exist--and, further, that the water, the bucket, the string, and the swinger would all cease to exist in present form--how could we say then what became of the water with respect to the bucket? There being no way to observe it? Or to gather a report from the swinger? Allow me though to use the frame of reference you advanced, as a starting point--a take-off point--for further (hopefully...) elucidation of the experiment in the earthbound frame of reference.

Of course, we could say that loss of any of the forces (yours and mine in particular) might cause escape of the water--after all, if one considers carefully, all the forces had to be present for the swinging scenario to commence to begin with. Then the question might be: which (presence or absence of fundamental force) is the most obvious to the senses--so that we could say we had a conclusive, observable solution to the question. To me, it would seem more be the gravity force which, if lost, could be identified as the proximate cause of water escape--hence, before that (reversing the order of events), conversely of water retention. While it's true that disintegration brought about by electromagnetic force loss would (somehow) alter the association between water, bucket, tether, and person--since all would instantaneously cease in present form at the instant of em force loss--no intelligent observation could attain (could deduce back) as to the em force's part in keeping water in bucket as a prelude to its loss from the bucket when em force not longer existed....said another way, nothing so radical as disintegration would be minimally required to part water and bucket.

In another vein, it also seems a might unfair to ask (for the questioner to have asked) which force compels the water to stay in the bucket when the presence of any force--and of one force in particular, gravity--is said (in effect in your rebuttal) not to necessarily be involved, even during the time of bucket orbit leading up to the time of one force's loss, that missing force which is to be identified as necessary to hold the water in the bucket. For the "experiment" or lesson to be valid, it would seem that all the forces must be actual candidates. Or at least that was my reading of the lesson attempting to be taught.

(I will dispense with further treatment of the alternate scenario—the lariat-to-bullwhip scenario—mentioned above as time does not allow… and it speaks sufficiently for itself without elaboration.

Please accept apology for my not being more concise (and precise), as more pressing matters than water pressing in a bucket forced me to throw this together more quickly and in more of an on-the-fly fashion than might normally have been the case. Please comment on any reasoning flaws or counterpoints, as I always look forward to correcting the errors of my ways. Thank you.

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#33
In reply to #27

Re: Forces of Nature

03/19/2007 12:28 PM

"To me, it would seem more be the gravity force which, if lost, could be identified as the proximate cause of water escape--hence, before that (reversing the order of events), conversely of water retention."

I am sorry but I must disagree. If gravity ceased to exist then the result would be that both the bucket and person spinning the bucket, would both rotate around the center of gravity of the two. It's analogous the Moon orbiting the Earth. In reality the Moon and Earth orbit each other around the barycenter. It is the inertia of the person that is spinning the bucket that allows the bucket to move in a circular path and inertia or mass of an object is independent of gravity.

Mass and weight are two completely different things. The mass of an object is defined as its ability to resist a change in motion. The weight of an object is the force that is exerted by a given mass while being affected by gravity and is proportional to the gravity.

Remove the gravity and the weight of the person spinning the bucket becomes zero but their mass remains the same and the mass is what is important not the weight.

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#49
In reply to #33

Re: Forces of Nature

04/06/2007 10:11 AM

You just a whole new dimension for my brain to process. If the gravity disappeared I guess you would start rotating opposite the bucket of water. I would love to see this experiment performed in a vehicle as it was leaving the earths gravitational pull.

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#6

Re: Forces of Nature

03/16/2007 4:53 AM

"There's a hole in my bucket, Dear Liza, Dear Liza..."

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#20
In reply to #6

Re: Forces of Nature

03/16/2007 3:29 PM

"Then fix it, Dear Henry, Dear Henry..."

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#28
In reply to #20

Re: Forces of Nature

03/19/2007 9:26 AM

"With what shall I fix it, dear Liza, dear Liza?"

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#29
In reply to #28

Re: Forces of Nature

03/19/2007 12:02 PM

"With straw, Dear Henry, Dear Henry..."

If we keep this up, we shall undoubtedly drive the rest of the group crazy.

You wanna?

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#30
In reply to #29

Re: Forces of Nature

03/19/2007 12:15 PM

"But the straw is too long, Dear Liza, Dear Liza. The straw is too long, Dear Liza, too long."

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#32
In reply to #30

Re: Forces of Nature

03/19/2007 12:28 PM

"Then cut it, Dear Henry, Dear Henry, Dear Henry -

Then cut it, Dear Henry, Dear Henry, cut it."

(We need sound. This isn't nearly annoying enough without the music.)

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#34
In reply to #32

Re: Forces of Nature

03/19/2007 12:43 PM

"With what shall I cut it, Dear Liza, Dear Liza? With what shall I cut it, Dear Liza, cut it?"

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#35
In reply to #34

Re: Forces of Nature

03/19/2007 4:41 PM

"With the axe, dear Henry, dear Henry, dear Henry; with the axe, dear Henry, dear Henry, the axe."

(Henry seems a bit dim, eh?)

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#36
In reply to #35

Re: Forces of Nature

03/20/2007 4:22 AM

"The axe is too blunt, Dear Liza, Dear Liza. The axe is too blunt, Dear Liza. Too blunt."

(Keep going!)

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#37
In reply to #36

Re: Forces of Nature

03/20/2007 12:45 PM

"Then hone it, dear Henry!"

(Liza getting a bit exasperated here.)

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#38
In reply to #37

Re: Forces of Nature

03/20/2007 12:58 PM

"With what shall I hone it, Dear Liza, Dear Liza? With what shall I hone it, Dear Liza? With what?"

(Henry clearly isn't a mechanical engineer...)

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#39
In reply to #38

Re: Forces of Nature

03/20/2007 7:28 PM

"With the wheel, dear Henry..."

(Liza hangs tough, refuses to give up & do the job herself!)

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#40
In reply to #39

Re: Forces of Nature

03/22/2007 5:02 AM

"The wheel is too dry, Dear Liza, Dear Liza. The wheel is too dry, Dear Liza. Too dry."

(Henry isn't a chemical engineer either...)

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#41
In reply to #40

Re: Forces of Nature

03/23/2007 1:51 PM

"Then wet it, dear Henry, dear Henry, dear Henry..."

(Sharpened or not, she's getting ready to use that axe.)

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#42
In reply to #41

Re: Forces of Nature

03/24/2007 12:57 AM

With what shall I wet it dear Liza dear Liza, with what shall I wet it, dear Liza, with what?

(Henry isn't any good at sharpening thing either, or perhaps he is and is hoping that Liza doesn't have a clue what to do next)

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#43
In reply to #42

Re: Forces of Nature

03/24/2007 5:42 PM

"With water, dear Henry."

(And now to Don in the booth for commentary: "Liza's played a tremendous game so far. She's a tough, tough competitor, even under this unrelenting pressure. Notice she avoids the easy sarcasm here, and goes for the straight answer! But the strain has got to be taking its toll, and I can't help but wonder: Can she maintain her focus, or will she start to slip as we near the final moments of this match??")

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#44
In reply to #43

Re: Forces of Nature

03/26/2007 3:54 AM

"And how shall I fetch it, dear Liza, dear Liza? How shall I fetch it, dear Liza, fetch it?"

(Henry clearly isn't a logistics manager either...)

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#47
In reply to #44

Re: Forces of Nature

03/26/2007 10:58 AM

"With the bucket, dear Henry, dear Henry, dear Henry..."

(Ooh! Liza slips up at last! Will Henry spot his opportunity??)

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#48
In reply to #47

Re: Forces of Nature

03/26/2007 11:09 AM

(Yes)

"But there's a hole in my bucket....."

(Yippee: got there!)

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#31
In reply to #29

Re: Forces of Nature

03/19/2007 12:21 PM

Don't worry, AstroNut, most of us are crazy already.

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#7

Re: Forces of Nature

03/16/2007 6:11 AM

Inertia. This is caused by rotation of the bucket relative to distant matter in the Universe, which gives rise to the phenomenon of centrifugal force (Newton would have said relative to absolute space, but that view is not accepted nowadays). Because if there were nothing in the Universe except you and the bucket and string, centrifugal force would not exist, as there would be no concept of rotation; nothing to rotate relative to.

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#8
In reply to #7

Re: Forces of Nature

03/16/2007 6:52 AM

Hi Codemaster,

Inertia is not one of the fundamental forces of nature. Inertia is a property of matter and is its ability to resist a force, so it's not a force in itself.

The question states which force can you remove or give up that will cause the water to leave the bucket.

So which one, strong nucleic, weak nucleic, electromagnet or gravity is holding the water in the bucket?

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#11
In reply to #8

Re: Forces of Nature

03/16/2007 9:15 AM

Hi Masu, that's a good point, it's not among the 4 fundamental forces as you say. But it leaves me wondering what force does give rise to the tension in the string? I don't think it's any of the 4.

It's nothing to do with Earth's gravity, as the string tension would be the same if you were in inter-galactic space (tho you wouldn't have to spin it so fast to stop the water falling out). Einstein's Principle of Equivalence says gravity and inertial forces are indistinguishable (from inside a closed box) but I don't think that resolves it.

Incidentally my comment about empty Universe applies to linear acceleration as well as centrifugal force.

Going back a few years, if I remember right the source of inertia was a puzzle, perhaps there have been developments I'm not up with since then. One suggestion at the time was that inertia is due to other matter in the Universe, but varying inversely with distance R (not R-2 like gravity). Then for gravity, assuming large-scale constant density, the effect of matter in a shell of given thickness at distance R is independent of R, as the amount of matter in the shell, varying as R2, just balances the distance effect (also, a thought that just occurred is that at the centre of a shell the the force would cancel anyway). But for inertia (on assumption above) the effect increases with R, so distant matter has a greater effect. This would explain why inertia doesn't appear to vary with position. Another possibilty is that inertia might always act in the same direction, so it wouldn't cancel, even if it varied as R-2.

Anybody comment or bring me up to date?

Cheers..........Codey

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#12
In reply to #11

Re: Forces of Nature

03/16/2007 9:42 AM

Basically any force exerted by, so called, physical contact is an electromagnetic force as nothing really touches anything else. The charge in the electron cloud repels the cloud in the adjacent atom as it approaches so atoms don't actually ever come in contact with each other. The nucleus is a whole different matter though, but I understand that the weak nucleic and electromagnetic force have been shown to be the same thing. That brings it back to three fundamental forces, however, in normal life you will only ever come across gravity and the electromagnetic force.

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#13
In reply to #12

Re: Forces of Nature

03/16/2007 10:25 AM

Hello Masu, that's fine, but I'm not too sure it explains the origin of inertia.

Cheers......Codey

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#15
In reply to #13

Re: Forces of Nature

03/16/2007 10:46 AM

This is true and like you I am unsure it there is an understanding of what inertia is, except as a property of matter and a definition of it's mass.

Discussing it would mimic the "What is Space?" thread and since that led to the creation of the term cosmolograine, I am going to leave trying to figure it out alone for the moment.

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#14
In reply to #12

Re: Forces of Nature

03/16/2007 10:30 AM

Masu - another thing, this sounds like just the sort of subject FYZ, Jorrie and Roger Pink might be able to contribute to. Any idea how we can get them into the discussion?

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#17
In reply to #14

Re: Forces of Nature

03/16/2007 12:01 PM

Hi Masu and Codemaster:

I've been enjoying this discussion on inertia. A thought occurred to me--If we give up "String Theory, the problem "goes away"! OK, OK a stupid joke!

I do recall, however, a number of years ago, I used to subscribe to Scientific American and there was an article about this very subject. I need to research that again because it was not Einstein who broght this up, but Max Plank or Born or one of Einsteins's contempories...I don't recall exactly who. But the opinion of the article was as Masu stated " the pull of the distant matter". But, recently, I heard a discussion on some TV channel. It seems the consensus now is that inertia is an intrinsic property of matter that manifests itself whenever matter is accelerated...in the Physics sense,i.e., accelerated/decelerated or a change in direction.

I'm going to see if I can find that article and get back to you guys. Thanks

Hankt

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#26
In reply to #17

Re: Forces of Nature

03/19/2007 4:53 AM

Ernst Mach made some contributions, there's something called Mach's Principle, can't remember what it says but I'll check it out. The same guy that Mach no. for speed in terms of sound velocity is named after.

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#21
In reply to #14

Re: Forces of Nature

03/16/2007 5:30 PM

Codemaster: You asked, "Any idea how we can get them into the discussion?"

You can send private email messages to any CR4 member. Find a message from one of these guys, click on the name above the avatar, and extend a polite invitation to join the fray.

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#23
In reply to #21

Re: Forces of Nature

03/17/2007 11:43 AM

OK AstroNut, thanks, I'll try it...........Codey

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#16
In reply to #12

Re: Forces of Nature

03/16/2007 11:58 AM

I think you are on the right track but focusing on the wrong component. If we lose the electromagnetic force then perhaps the continuity of the bottom of the bucket goes away and the water will "spill" out.

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#18

Re: Forces of Nature

03/16/2007 12:03 PM

You will need to give up the centrifugal opposition force.

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#19

Re: Forces of Nature

03/16/2007 1:29 PM

friction

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#22

Re: Forces of Nature

03/16/2007 10:07 PM

One source of information is: Fundamentals of Physics; David Halliday, Robert Resnick; Wiley;1974. On page 49, there is a discussion on Uniform Circular Motion. Acceleration arises from a change in velocity. In uniform circular motion, where (here) a bucket is moving in a circle with constant speed, the velocity vector is constantly changing in direction, but not in magnitude.

On page 82 of the same source, there is a discussion of the Dynamics of Uniform Circular Motion. What we used to call Centrifical Force.

One way to remove the water without damaging the pail (no holes), no explosives, etc, would be to simply heat the pail (laser light, torch, ambient temperature, etc) and boil (or evaporate) the water out of the bucket.

As a chemist, I cringe at the use of "nucleic forces". We try to keep "nucleic" for DNA etc and nucleic acids. In nuclear forces, such as the strong nuclear force, the weak nuclear force, we try to relate the weak nuclear force to atomic radioactive decay, and the strong nuclear forces relegated to the inside of the atomic nucleus and nuclear particles. Sorry, I couldn't resist the comment!

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#24

Re: Forces of Nature

03/17/2007 10:44 PM

The kinetic force being applied to the bucket in what amounts to a mostly back and forth motion. Notice when you start to spin something on the end of a rope that for the first few revolutions you are spinning the object in a largely circular motion but after you get it moving at a certain velocity you can maintain the object motion with less of a y axis and more x axis movement of your arm. If you stop even one of these directions of movement for a few strokes, you will lose much water before you can recover the lost motion.

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#25

Re: Forces of Nature

03/19/2007 12:43 AM

centrifugal forcess

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#45
In reply to #25

Re: Forces of Nature

03/26/2007 7:44 AM

If centrifugal force is the official answer than I must disagree.

The centrifugal force is a fictitious force, for it to exist you need to ignore the constant strength but rotating force, that is applied to the bucket which is causing it to travel in a circular path.

Put bluntly there is no such thin as centrifugal force.

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#46
In reply to #45

Re: Forces of Nature

03/26/2007 10:57 AM

My dad, a physics teacher & textbook author, always said that it's properly called the centrifugal reaction.