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Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

Posted May 05, 2007 5:01 PM
Pathfinder Tags: challenge questions

The question as it appears in the 05/08 edition of Specs & Techs from GlobalSpec:

A physicist played a prank on his friend by placing a large spinning wheel inside a suitcase. He asked his friend to go to the next room and bring back the suitcase. His friend picked up the handle of the case in his left hand, unaware that the wheel was spinning inside in a counterclockwise motion, with the top of the wheel moving towards the front of the case. What happened to the case when his friend exited the room and made a left-hand turn?

(Update: May 15, 8:44 PM EST) And the Answer is...

The case pivoted top over bottom due to gyroscopic motion. The top of the case rotated sideways towards his friend's leg while the bottom of the case rotated upwards, away from him. Gyroscopic motion is fairly complicated, but can be explained by picturing the spinning wheel as a square ring with a heavy fluid flowing through it. As the friend turns left, the fluid flowing in a vertical (up or down) motion does not change direction. The fluid flowing horizontally, does change direction as the case is turned. A portion of the fluid that is flowing vertically (up or down) is forced to travel in a curve as the friend turns left. This exerts a force on the side of the case, forcing the bottom to lift away from the friend and the top to rotate towards him. The resulting motion of the rotating wheel is exactly the same as the fluid flowing through the square ring.

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#1

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/05/2007 9:47 PM

Motorcyclists will like this question. At any reasonable speed, when you turn the handlebars to the right, the bike banks to the left. In the motorcycle, two things cause this. The contact patch is steered out to the right, causing a torque around the cg of the bike, in turn causing the bike to bank to the left. Gyroscopic precession has the same effect: turning the front wheel to the right causes the front wheel to try to bank to the left.

So in this case (ho ho) if the top of the wheel is moving toward the front of the case, then the case will try to tilt to the right as the friend tries to turn to the left. At the same time, the case will try to resist any turning motion. It would come as quite a surprise.

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#2

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/06/2007 3:32 AM

Sound like the friend is going to fall over or break his wrist/trip over the case. It depends on the persons size, shape etc. The wheel will not want to change , but if you force it , somethings going to compensate.

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#3
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/06/2007 11:29 PM

I do believe that the bottom of the case will want to take a bite out of his ankle.

RichH

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#5
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 3:34 AM

I think Blink has it right; the tilt would be top to the right, bottom to the left, moving away from the guy's ankle!

-J

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#12
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 8:56 AM

You're right, Jorrie. I missed the "left hand" in my read. Had it been his right hand, it would have wantted to bite his ankle.

RichH

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#40
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 11:48 AM

Blink has it wrong. He never said the bottom flips up and away. Since he was unclear I consider it wrong. You clarified, and kindly but incorrectly gave him credit.

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#45
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 1:39 PM

I think that, if you read some of Jorrie's posts, you will see that he has an excellent grasp of the English language. My guess would be that when he read my words "the case will try to tilt to the right," he interpreted that to mean that the case would exhibit a tendency to rotate clockwise, when viewed from the rear. Certainly, to suggest that the case is "trying" to do anything is anthropomorphising. Nevertheless, I think I can be excused the loose language, both because of the nature of the challenge (which describes a practical joke), and also because the wording "will try" fits well, in a literary sense, with the wording "tries to turn left" as it describes the action of the friend. The fact that Jorrie was able to interpret the language as I'd intended seems to support my contention.

Whether, in fact, the friend succeeds in actually turning the case to to left is unknown. An extended arm, carrying something like a suitcase, has both very low torsional rigidity and low torsional muscle strength, so it is likely that the carrier will walk into the suitcase before the suitcase rotates significantly counter clockwise, as viewed from above. The suitcase will then tilt to the left (CCW as viewed from behind) if the carrier's knee or thigh hits it first. But we cannot know this. Perhaps the ankle hits first.

So to keep things simple, one can say that the case will tend to resist any turning motion (that is what I was saying when I wrote "try to resist any turning motion"). If one were writing to someone without any understanding of gyroscopes, then one would want to be more specific re the axes of motion resisted. One could also say that the case will tend to "tilt", if the resistance to the turning motion just mentioned is overcome. In so "tilting," it will tend to rotate about the center of gravity of the gyroscope. In the question's scenario, the case would move in toward the carrier's upper leg at the top and out away from the ankles at the bottom. (When carrying a suitcase, the arm has almost non-existent lateral stiffness, with the shoulder joint acting as a pivot of a pendulum that can swing easily both for-and-aft as well as side-to-side.)

So you would need more information before you could say, with any certainty, that 1. any significant rotation of the case (as viewed from above) occurs before the carrier walks into it, causing perturbations that become quite unpredictable, given the unknown human inputs ensuing, or 2. that if the case is successfully rotated (CCW as viewed from above) that the "bottom flips up and away." Rather, the bottom would slowly move out (and the top would slowly move in) at a rate depending on the carrier's leftward turn rate. "Flip" connotes a faster motion than would likely occur.

But I think all that misses the point of the question, which seems to be looking for a simple, rather than comprehensive, answer. Based on that, I would be loathe to suggest that Jorrie failed to interpret my answer correctly. He's no dummy.

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#50
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 2:09 PM

An extended arm, carrying something like a suitcase, has both very low torsional rigidity and low torsional muscle strength,

Hope you'll understand if I don't call you to shut off my water supply in an emergency Ken. . I think you are referring to what will happen if the carrier is walking in a relaxed manner.

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#54
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 3:11 PM

I think you are referring to what will happen if the carrier is walking in a relaxed manner.

Sort of. Although even after he stiffens up after becoming terrified by the strange suitcase, unless he bends his elbow, his torsional strength is pretty poor*. If you ski, you will find that you have far more leverage over the skis with your knees bent.

Definitely don't call me in an emergency to turn off your water. By the time I book a flight, your place could be flooded.

* I just did a little experiment, and walked around the room while carrying a computer case. I actually leave my arm almost entirely loose, and steer the case with knee nudges, if I am turning toward it.

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#85
In reply to #54

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/09/2007 9:59 PM

Hi Ken

When the friend is turning to the left the suitcase will try to stay in the original angle blocking the friendĀ“s way.

CIRO

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#86
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 12:14 AM

Hi Ciro,

I agree. If the friend stiffened his arm in an attempt to make the suitcase turn to the left, (and if he succeeded in doing that) then the suitcase would tend to swing out away from the ankles and in toward the knees.

Ken

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#87
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 1:59 AM

According to my sources , if you force-precess a gyro (such as this ) that can not tilt it will exhibit pull along it's axis !. Ref - Eric Blaithwaite , Royal Institute Christmas lecture demonstrations 1974. I have a still photo of the set-up which I will post if requested (no need for un-requested pixels). I make no suggestion that his interpretation is correct , since he also suggest in the same breath that the gyro will rise vertically. Odd ?

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#95
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 6:17 AM

I think you mean Eric Laithwaite? Great inspirer, but I treat detailed technical output with extreme caution.

Fyz

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#114
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 12:25 PM

Yes , I'm a blumsy speller. Anyway some people use thread to cheat.As the saying gos "Trust no one".

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#121
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 3:23 PM

Sorry about that - it was clumsily put . The only reason for my comment was in case anyone might wish to look up the said gentleman.

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#129
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/11/2007 12:46 AM

No problem . I've already hyperlinked him some place. My character is too much like my Squirrel picture !

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#7
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 5:01 AM

As the man turns the corner , he is forcing precession. This will result in the case rising or dropping vertically (depending on how you interpret the view on counter-clockwise). So it's either case in armpit or case is 'heavy'. I rest my case.

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#9
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 7:01 AM

Here are some toys to play with.

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#27
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 4:59 AM

That should read some toys . Have another

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#28
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 5:14 AM

You have a veritable treasure trove of information for us here - I just wonder how much more there is that you couldn't remember where it was stored last winter.

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#29
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 5:35 AM

...... Put it this way , I seem to loose more stuff than I remember ! Trying to find it is half the fun.

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#30
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 6:06 AM

It always surprises me that there are no bald squirrels, but maybe they're just more chilled than eagles.

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#38
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 10:42 AM

Bald Eagles aren't reallly bald. They just have a white feathered head that sets them apart visually from other eagles.

I did however observe albino squirrels around my home when I was a kid. Then of course, there are naked mole rats!

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#39
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 10:56 AM

The Sphinx aint got much har niether

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#31
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 6:39 AM

I preferred his old persona; at least you know where you are with Old Nick. That Squirrel Nutkins looks positivelt deranged!

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#32
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 7:07 AM

You'll note that my newly acquired ears are pointy - this may be a costume to deceive. There is only one Nutkin , thank you very much. "There can be only one" . And yes I am completely deranged. It takes years to dance like this you know. This is why I could handle the case in question.

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#34
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 9:54 AM

positivelt = positively svelte?

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#37
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 10:34 AM

triping error noticed as I hit submit...then had to take phone call so missed the 15 minute window to edit.

BTW - conservation of angular momentum like what he said!

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#41
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 12:38 PM

Pah ! It was a Freudian slip . Unless you had your longbow and I looked 'luxuriant'

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#48
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 2:02 PM

Rose - You said it was a "triping error"?

For me, a triping error is any recipe that actually involves tripe.

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#51
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 2:35 PM

I don't want to split hairs here (), but triping does not refer to any recipe in which tripe is involved, but only some. Rather, triping is the practice of threading strips of tripe through a piece of meat to make it less tender. You are probably familiar with the practice called "larding," which is used in French cooking to insert strings of fat into a piece of meat. Triping is just the opposite.

Tripe can also mean "nonsensical utterances". Therefore, one could say I have been triping in this post, provided one is not offended by the creation of verbs willy-nilly from nouns (a practice called verbifying).

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#60
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/09/2007 12:31 AM

No , you're both wrong. ER was holding a packed case , gazing out of the window , before turning to hit return with a serene but decisive farewell tap. The case was rigged so she couldn't leave. I had not foreseen the tripping.

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#64
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/09/2007 3:12 AM

That should have read TRYPING error. Hope all is clear now. My apologies for any confusion.

Tripe - that's the foul smelling cow's stomach we fed to our dog after she'd whelped.

ER leaves the room, having flattened Kris with the case for the attempted imprisonment, and trips lightly down the stairs, all ready for her day trip with the OAPs to the tripe factory.

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#71
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/09/2007 6:53 AM

It wasn't me , it was Blaine . The fiend.

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#35
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 10:13 AM

A very nice present! I note that nutation is discussed, a topic which would have to be of great interest to someone as squirrelly as you.

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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 9:49 PM

Very good Kris!

I liked the link, it sounds like the "they" here, have done a little plagiarizing as needed to find something to challange.

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#44
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 1:33 PM

Sorry, Kris, you better rest your case somewhere else. The man does not feel a vertical force, neither in his armpit nor pulling down. What he feels is a torque, which results in a rotation of the case. Since his is holding the handle at the top, the torque results in a force laterally (in the horizontal plane), not vertically, against his hand, while at the same time an equal and opposite force acts at the bottom of the case to rotate the bottom, assuming he holds the top firmly and it remains motionless.

Depending on your perspective or assumption of what is CW or CCW, it will either swing up against his leg or up and out, away from his body. Based on the direction of travel and the phrasing of the question, I believe it will swing up and out.

See my posting #13 below for more info.

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#47
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 1:58 PM

Yes , my use of 'heavy' was clumsy . I was (too) hastily alluding to which way the case was swinging about it's handle. The links I have given allow you to see this all quite clearly with suitcase and all.

As to the direction , I've already covered the ambiguity of CW/CCW

The man is forcing the case to turn about a vertical axis , not the other way round. He twists the case and it rises , but it will not weigh any more than it did when he picked it up.

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#63
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/09/2007 1:01 AM

For those who didn't follow the earlier link , look at this. The parameters are slightly different - you'll have to look at the original link to see why the question posed is a sort of mirror to the vid-clip.

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#4

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 1:13 AM

Nothing, this horizontal to the plane, if he were perpendicular you would say clockwise or counterclockwise, where if it would act like gyroscope.

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#6

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 4:24 AM

I'm with Grage Tesla in assessing the outcome, but I disagree with his conclusions. If the friend's motion is in the plane of the axis around which the gyroscope is turning, the direction and height of the case will turn with the bearer and gravity; and I think the vertical attitude of the case would remain the same as it was when the case was at rest, regardless of which direction the gyroscope spins.

But the puzzle gives us a clue when it mentions the top of the wheel, which seems to indicate that the gyroscope's initial attitude is a vertical position, so the friend is not in the plane of the gyroscopic axis. I think that in the given scenario the motion of his turn would be resisted by the case, again regardless of which direction it is spinning.

In a sense, the same thing is happening to the motorcycle, which has developed a sense of gyroscopic attitude as it speeds along, so that an attempt to change its direction at speed would result in a resistance that seems to be in the opposite direction, but in fact just wants to continue straight along in the same plane of travel, which is one good reason to slow down when one is making a turn in any vehicle.

Mark

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#57
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 3:58 PM

Mark, I think you are confusing the Newtonian concept of conservation of linear momentum with the gyroscopic effect brought on by conservation of angular momentum in your motorcycle example.

In the motorcycle example, you would experience both when making a turn. The mass of the motorcycle wants to continue in a straight line due to linear momentum. In a car, we call this effect body lean. With friction from the motorcycles tires resisting the original direction while turning left, the mass of the rider and the mass of the motorcycle would tend to lean to the right, experiencing a torque (force x distance from pivot point to the center of mass).

The force is the so-called "centrifugal force", which only applies in static equilibrium of the mass along its (constant) radius, like the tension in a weighted string that is swung around. Cut the string and the weight will not fly off along the radius, but along a tangent to its orbit. That is why we say it is a so "so-called" force.

Due to conservation of angular momentum, the motorcycle wheel acts just like our wheel in the suitcase, except in this case the "handle" is on the bottom, at the pavement (friction). Torque is the same, but instead of the bottom swinging up and left (it can't or else you have a skid), the wheel and its axle (axis of rotation) will tend to pitch the cycle and rider over to the right as well. That is why a motorcyclist will lean into the turn, allowing gravity to help him overcome these two force trying to flip him over to the right as he turns left. It is difficult to duplicate this maneuver in a car!

Except for the linear momentum, this is the same thing that happens when a balanced gyroscope toy set on its end seemingly defies gravity as it slowly gyrates around while held at only one end.

In the suitcase example, linear velocity is relatively low, so there will be negligible amount of linear momentum to overcome and it is what we expect anyway. The unexpected forces on the suitcase come from conservation of angular momentum and resulting torques.

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#8

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 5:58 AM

The bottom will go left away from the ankle. This can make checking into a swanky hotel fun when they grab your bags to take them to your room.

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#10

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 7:44 AM

I think that this problem has to do with spinning force...L..of the wheel-suitcase system..I will come up with a solution tommorow...

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#11

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 8:32 AM

I'm assuming he is facing the door when he lifts the suitcase and does not have to turn prior to exiting the room and that the "front" of the case is facing the door as well ....

the following will likely happen:

1) lifting the case and carrying the case should be uneventful....

2) but at the corner he'll wrench his wrist and

3) trip into the case as if it were a german shepard...

4) likely, he'll trip over the case and break some furniture...

5) he will be rushed to the hospital ....

6) and the police (and/or hotel security) will investigate ....

7) and the physicist will be in deep, hot water...

8) the friend will contact his lawyer....

9) the physist will contact his lawyer .....

10) .............!!!!!!! .............

at least that's the way I see things playing out......

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#75
In reply to #11

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/09/2007 7:18 AM

Yes, the police will investigate and will uncover an international ring of spinning wheel smugglers!

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#13

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 10:03 AM

"His friend picked up the handle of the case in his left hand,"

This tells us the relative position of the case to the friend, assuming the friend is facing the door of the room at the time he picks up the case. IF so, then the case will be on the friends left side.

"unaware that the wheel was spinning inside in a counterclockwise motion,"

This is ambiguous, because the wheel would appear to be turning CW when looking from one side, but CCW when looking from the other side.

"with the top of the wheel moving towards the front of the case."

Assuming that the "front of the case" means the leading edge, closest to the door, we now have a better idea of the relative position and spin of the wheel inside the case.

"What happened to the case when his friend exited the room and made a left-hand turn?"

Assuming the handle of the case is exactly in the middle of the top, centered front to back and side to side, the gyroscopic effect caused by the rotating mass of the wheel (assuming it is firmly attached to the inside of the case) due to conservation of angular momentum (Moment of Inertia x Angular Velocity) would cause a torque on the axis on which the wheel was spinning, which we must assume is at about the mid-point of the case from top to bottom. This torque would apply a force at the handle toward the body and a force at the bottom away from the body. Assuming the handle is mounted on a pivot, the friends hand/arm strength resists this force, but the bottom is free to swing out and up, resisted only by gravity.

The friend would be very surprised as the bottom of the case attempted to swing up and away from him. Normally, he would have expect it to simply resist being turned to the left due to conservation of linear momentum in proportion to how fast he was moving when he turned left and how quickly he attempted to turn the case. Now the case seems to have a mind of its own and wants to rotate CW (as seen from the rear).

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#14

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 12:05 PM

It would be nice to be given enough information to solve this little riddle.... For instance: is the suitcase laying flat (and therefore the wheel within it is in a horizontal position like that of a roulette wheel), or is the suitcase standing on it's side (and the wheel also on it's side (edge) , like that of a motorbike)? Normally a suitcase is carried by the handle with the broad sides parallel to the sides of the person doing the carrying. If that is the case, then the wheel is on edge and the effects would be dramatically different than if the suitcase were to be carried flat with the wheel spinning horizontally like a roulette wheel. With the suitcase on edge, the wheel would be spinning in a forward direction, and the left turning carrier would walk into it if not, quite possibly, trip over it in the attempt to make that left turn: the rotating wheel would resist the turn and instead attempt to continue with its forward momentum. If the suitcase were to be carried flat, then making the same left turn would attempt to cause the carrier to be spun around the axis of the wheel in the direction of the wheels' spin, being that the wheel and turn were in the same direction, but unless the mass of the wheel were greater than the mass of the carrier, the inertia of the one would out weigh the inertia of the other, and the most that a burly suitcase carrier may feel is a tug to the left (counterclockwise, as seen from above)...

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#180
In reply to #14

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/15/2007 8:03 PM

The simple rule of thumb here is that a sideways force applied at the rim of a spinning disc takes effect 90 degrees in the direction of rotation. As the disc is spinning on an axis, these forces are actually applied to the axis. For ease of explanation, a corresponding point on the rim of the disc is used.

Increasing gyroscopic inertia ( weight of the disc / rpm ) will increase the 'resistance' of the disc's axis to being moved offline. The force applied in turning the suitcase left would need to be great enough to overcome this inertia and cause the axis of the wheel inside to be moved, the 90 degree rule can then take effect.

To keep the original problem simple, turning the suitcase to the left will apply opposing forces to the rim of the spinning wheel. Turning the case to the left is effectively applying forces to push the front of the wheel left and the back of the wheel right. As those forces take effect 90 deg in the direction of rotation, the wheel will tilt sideways along its axis, with the handle moving towards the carrier and the bottom away from him.

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#181
In reply to #180

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/16/2007 4:47 AM

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#15

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 12:45 PM

Yeah, gyroscope; opposed to any change on the perpendicular axis. The suitcase won't turn when he does, making for some serious grins and laffs..

IMO- it wouldn't matter -the direction of rotation; cw or ccw. The effect would be the same.

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#16

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 2:42 PM

Some of you guys should read up on gyroscopes and precessing. The gyroscope does not just resist being rotated. It actually creates a torque in the plane perpendicular to the plane of spin as it is rotated. And, yes, there would be a difference between CW and CCW spin. The torque would be in the opposite direction if spin is reversed.

In this case (pardon the pun), if the wheel were spinning in a clockwise (CW) motion, as seem when looking at the man and the case from the man's left side (from down the hallway), with the top of the wheel moving away from the front of the case (see my posting above for other assumptions), then the torque generated by a left-hand turning of the case would cause the case to move its bottom toward the person and its top away. Since the person has control of the top by its handle and it cannot rotate CCW, as seen from the rear, the bottom of the case would lift up and hit his leg as he turned the case.

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#17
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 2:52 PM

oh yeah..forgot about that.

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#18

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 3:08 PM

Arthur Webster of Clark University played pranks like this. The excerpt below is from this site.

Indeed, physicists always enjoyed meeting Webster on his arrivals at railroad stations for Webster liked to play practical jokes of a scientific nature. Webster, with his expertise on the gyroscope, had constructed a portable, battery-powered gyroscope housed in a suitcase. As his train would come into the station he would start the gyroscope. Once the gyroscope was up to speed he would hand this suitcase to a porter with instructions to take good care of it. Webster would then walk briskly down the station platform, making abrupt turns as he went. The suitcase, however, would not follow these turns, shooting off into space with an alarmed porter hanging on desperately and with the assembled greeters responding with hilarity.

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#19
In reply to #18

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 3:15 PM

That's funny. We need more scientific practical jokes. Where I work they used to hook up capacitors backwards in the benches so that when power was applied...bang!

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#25
In reply to #18

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 12:15 AM

Ken , My post#9 has 2 links . Click on the word some and you will find an animation to tinker with.

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#20

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 3:17 PM

Unless of course he pricks his finger on the spindle, causing a deep sleep broken only by the kiss of a prince/princess...

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#21

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 3:18 PM

I wonder, do they still make those toy gyroscopes, the kind with the welded wire outer cage, with two bearings holding the heavier cast rotor? Usually the rotor was colored red or some other anodized finish, while the cage was usually silvery, chrome plate I think. The rotor had a black rubber wheel on one side of its axis that allowed you to "rev it up" by friction, usually along a table or counter edge.

The cage axis (parallel to the rotor axis) had a ball on one end and a V-groove on the other. The ball allowed you to place it on a raised point, preferable with a small dimple to hold it in place and the whole thing was balanced so that when the axis was horizontal the torque due to gravity was countered by the torque of precessing and it would "balance" at a right angle to its stand. That is, if you had spun it in the correct direction relative to which end was supported. Otherwise you had a flop, literally.

I am not sure what force made it rotate slowly around the supporting point. I suppose the concept works in reverse as well, since the torques were counterbalanced (gravity and precessing torques) and static in the vertical plane, then there would be a resultant torque in the horizontal plane, right?

The V-groove was handy for making it do tricks on a string, wire, or thin edge.

Man was that cool! Nowadays, if it doesn't BEEP, or light up, or make digital "music" and have a video display, I guess it would be "lame" for kids, right?

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#22
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 3:22 PM

I think Edmund Scientific still carries a few of the ole-fashioned ones.

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#24
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 5:44 PM

Hi STL Engineer,

Last time I checked (2-3 years ago), The Discovery Store carried these gyroscopes.

Regards,

John

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#26
In reply to #21

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 12:20 AM

How about these.

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#36
In reply to #21

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 10:29 AM

Hi STL,

I am not sure what force made it rotate slowly around the supporting point. I suppose the concept works in reverse as well, since the torques were counterbalanced (gravity and precessing torques) and static in the vertical plane, then there would be a resultant torque in the horizontal plane, right?

You'll probably like the simulator in Kris's post #27. There are links to papers with additional info. Have fun.

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#42
In reply to #36

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 12:49 PM

And look at #26 STL ! Get toys ! Get Toys ! Everybody get the toys out ! If you can't find one , make one ! Proof by experiment ! Now , Now ! Quickest ever agreed outcome of Question ever !

Darn. I forgot this was CR4. 'depends which way is clockwise , If the man exited into an elevator .......'

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#43
In reply to #42

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 1:02 PM

I like the rocket with the video camera built in. Yep, Get Toys!

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#79
In reply to #21

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/09/2007 8:06 AM

"I am not sure what force made it rotate slowly around the supporting point." I suspect you know full well that it was a torque set up by gravity (downwards at CofG) and the support (upwards at the resting point). I suspect you are simply trying to persuade someone to come up with a general explanation of gyroscopes within the thread - and I'm a sucker for that.

The cause of the effect is conservation and generation of angular momentum. If you had managed to rotate the axis around the axis of the applied torque, the wheel would now have angular momentum in a direction that is perpendicular both to it's original direction of rotation and to the direction of the torque; that is, you would have changed angular momentum about an axis without applying a torque. So the axis cannot rotate in the direction of your applied torque. At the same time, the torque you are applying has to change the angular momentum about its own axis; the only way that both requirements can be satisfied is by the axis of rotation turning about an axis that is perpendicular both to the applied torque and to the original axis of rotation.

BTW, this leads to a fun little paradox: the argument applies however slowly the object is rotating initially. So how come that in practice objects that are rotating very slowly appear simply to start rotating along the direction of the applied torque?

Enjoy

Fyz

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#23

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/07/2007 4:04 PM

Gyroscopes exhibit rigidity in space. The apparent torque would be precessed by 90 degrees from the real torque caused by turning the corner. If the Gyroscope is attached to the case so that relative movement of the case puts a torque on the gyroscope, the case would try to move left or right, depending on the direction of rotation.

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#33

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 7:24 AM

The tale was told by either Camus or de Maupassant (my memory fails me...) of this trick being played on a porter at a French railway station. The consequence was one dropped suitcase, and the immortal line "Le diable soit ete la dedans".

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#46

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 1:54 PM

My dad, a physics teacher, had a bicycle wheel with the tire filled with sand. The axle was connected to a handle on each side. A student would sit on a bar-stool, holding the wheel vertically with both hands, arms extended. Then Dad would spin up the wheel and ask the student to tip it right or left - and the student would spin on the stool! Great fun, lots of laughter, and none of the kids ever forgot that lesson.

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#49

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 2:03 PM

It is my understanding that a gyroscope can be moved along any plane through space on any axis, it's only when you try to rotate it then there is resistance. Otherwise, you could build an anti-gravity device. The briefcase can be picked up. swung side to side and front to back with no problem but the top, bottom and sides will remain at the same angle vector that that it started with.

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#52
In reply to #49

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 2:49 PM

True. And it can be rotated easily along the gyro's own axis of rotation. So swinging front to back is easy, with the top and bottom changing angle freely.

Otherwise, you could build an anti-gravity device.

Yikes! Don't give anyone ideas. Just when there is a lull in the perpetual motion machine threads, someone will claim to have created an anti-gravity machine based on a gyro, and will further claim that there are many replications being completed even as we speak!

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#53
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 3:10 PM

oOps--yeah I remember that happened on another thread not too long ago- don't want to repeat that

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#61
In reply to #52

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/09/2007 12:46 AM

Otherwise, you could build an anti-gravity device.

I have a picture of a young child appearing to lift a 23lb weight at arms length.

I wont post the pic because people may not believe without a full video. Mini-Hercules does appear to lift the weight ( and all BBC viewers will know this ).

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#55

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 3:21 PM

Unless I'm mistaken, the greater the mass of the wheel of the gyro the more resistance it can make against rotation; also the speed (?)Therefore if you put a 150 lb wheel in the suitcase spinning at 10,000 rpm, the person carrying it would probably break their neck trying to turn it around a corner

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#56
In reply to #55

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 3:53 PM

See what can be done with large flywheels, in this case, 1200 lbs, but turning at only 2000 -3000 rpm.

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#62
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/09/2007 12:52 AM

Very cool. It's now up there with 'spider car' on my Christmas wish list.

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#58

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/08/2007 7:08 PM

If the wheel is spinning he could never place the spinning wheel in the suitcase in the first place! So the first part is WRONG! My guess the wheel is spun in the suitcase with the suitcase in the correct orientation.

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#65

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/09/2007 3:37 AM

Due to the gyroscopic effect, the case will turn around an horizontal axis in such a way that the bottom of the case will press against his leg and the handle will pull his hand outward.

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#66

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/09/2007 4:16 AM

I'm not contributing to the answer for the problem with this reply but instead share an interesting thought which I've had since reading the replies.

Although I've known about the gyroscopic effect as described, I've never stopped to think how much it contributes to the large numbers of industrial accidents that take place with personel using 9 inch angle grinders.

9 inch angle grinders, especially when used [legally] with a cutting wheel -instead of a grinding wheel- for cutting purposes cause so many serious injuries to the operator that they are very nearly banned on every industrial site where I've worked. By very nearly banned I mean that there is strict enforecement that only specifically trained operators may use them.

I've never stopped to think that the artful manouvoring of a high speed spinning 9 inch stone/metallic disk is met with what probably seems like a totally random response from the disk, hence the accidental carving into one's own leg / body.

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#67
In reply to #66

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/09/2007 4:26 AM

Thank you Guest, that's a very good point, and one which I, and I guess many other here, wouldn't have considered. Perhaps we should patent a double disc-ed grinder in order to remove this effect? (Ooops! Idea's in the public domain, so no patent rights for anyone!)

Whilst my idea is slightly tongue-in-cheek, if only for cost reasons, what are people's thoughts on incorporating a contra-rotating disc in order to cancel out the gyroscopic effects? Would it work? <ER nudges Jorrie>

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#68
In reply to #67

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/09/2007 5:18 AM

Cheers for that English Rose.

I guess the counter disk would need to be a rotating counter weight of smaller diameter to the main cutting disk so as to not interfere with the cutting / grinding action.

So could a 2nd smaller diameter disk/weight, being thicker or constructed of heavier material as required, rotating in the opposite direction to the main cutting disk effectively counter the 'seeming random response' exhibited when manouvering the grinder.

If so, it would certainly be a very worthwhile investment for a manufacturer, the device would sell. Even experienced operators still have very serious accidents.

PS, quite some accidents are caused by the operator fighting the grinder's uncontrollable movements which can twist the cutting disk in the job, causing it to grab and then the whole grinder is thrown out of the job ... -if you get what I mean- into .. the operator.

The best available solution at the moment is that manufacturers have designed brakes into the grinder so that it stops immediately upon letting go of the trigger. This has not helped at all as the accidents happen before the operator himself realises.

Seriously, if it could work, it would sell even if it doubled the price of the grinder.

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#69
In reply to #68

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/09/2007 6:04 AM

Perhaps you and I should set about designing it and then sell the idea to the manufacturers.

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#73
In reply to #69

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/09/2007 6:59 AM

Maybe the false sense of security is not worth the money that could be invested in ballistic-nylon pants.

I know people who handle jagged material without gloves - they fair better than most who use gloves , because they're careful.

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#88
In reply to #69

Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 2:45 AM

Hi, Rose

Although I retired from engineering in 2000, due to the vagaries of the stock market I had to go back to work; but not too much, and at something I enjoy doing. So I really am a professional handyman.

Just now, I am installing a steel door into a brick opening in the side of a two-car garage. The steel door jambs are designed to wrap around an exterior door frame, and the brick face on the door opening is too wide to allow this to happen. So I must cut grooves in the brick to recess the door jambs 1/4 inch on either side. A standard masonary saw would be too awkward for this amount of precision, and heavy besides. So I shall be cutting the brick with a 4-inch grinder using a diamond cutting wheel to a depth of 1/4 inch and a width of 1/2 inch, and chiselling out the groove with a peumatic chisel.

To retain control of the cut, I had to design a shoe for the grinder similar to that used on a circular saw to limit depth, provide a holder for a rip fence to keep the grinder in a straight line, and be tiltable so that an angle cut may be made. I'm hoping that the shoe will provide enough stability to keep my workplace safe. I was informed by Bosch Tools that they used to make one of these, but no longer do. My design is simple and should fit any grinder. Pardon my sketches:

Seems to me such a device might, hopefully, add to the stability of a 9" blade being used for cutting, since the grinder is a two-handed tool and the base would provide the third point of control, with the rip fence guiding a straight cut.

Mark

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#90
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 4:48 AM

I just fitted a grinding disc to my circular saw for accurate cutting. The problem with depth is that the plate needs adjusted regularly, as the disc wears.

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#91
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 4:58 AM

Back to topic with a very serious question - does anybody know why the millemium wheel is falling over ?

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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 5:07 AM

It was built to modern standards: (what we think it may be subjected to) x6.

Any under-estimation can multiply to erode the safety factor of even one element, that all the rest rely on.

All it takes is a tiny amount of extra stretch in one cable to eventually upset the whole construction.

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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 5:45 AM

'Give me a place to stand and I....' , or maybe get two men and a rope .

Brilliance .

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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 6:00 AM

"planning permission for 5 years, but built to last longer"........................

I wonder how often they check the spoke tensions and balance?

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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 7:03 AM

Isn't the land leased ? Hey , Tony is formally saying 'I'm going' RIGHT NOW.

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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 8:59 AM

Are you saying that Tony Blair is resigning because he is afraid the Millenium Wheel will fall down on his watch?

ROFLOL!

That doesn't say much for the British Parliamentary System, the Labor Party, or Mr. Blair in particular. Whatever happened to that famous British "Stiff upper lip", and all that, tut, tut! Is this the same Britain that survived the Nazi blitz and the introduction of American-style football? I can hardly believe it.

Next time, bring in a few Scottish Engineers to do the job right! <grin>

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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 9:09 AM

Don't know that there's many engineers left here, but neither a majority of Labour politicians (for the first time in 50 years)

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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 9:17 AM

You are probably right. All the great Scottish Engineers probably emigrated to the US, Canada, or Australia!

However, there is at least one leading Labourite in Edinburgh (Portobello, to be more precise), my cousin's Husband, Lord Macaulay of Bragar!

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#101
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 9:25 AM

Funny how it was the Scots who were the engineers and the leading lights in creating the Empire (can you tell I used to live with a Scotsman?) but it's the English who get the blame for colonising...

I'll admit to Wales but nothing else!

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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 9:30 AM

Engineers provide solutions for the problems they see, but they have no control over how the products are used........MacAdam must be spinning in his grave with all the humps deliberately spoiling his product!

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#105
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 9:41 AM

Wasn't it someone from East Anglia that sent the Scots to "pacify" Ireland? (Perhaps the mistake was to fail to ensure that all these Scots were of a single religious persuasion?). But maybe fear of this made the Scots more ready to go and administer the furthest reaches of the empire. Is this thread spinning out of control?

Do I see a yellow rose with a long trumpet sharing space with a non-bulbous member of the onion family?

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#106
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 10:08 AM

"Do I see a yellow rose with a long trumpet sharing space with a non-bulbous member of the onion family?"

Non-sequitor. Are you referring to leeks and some sort of garden plant?

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#107
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 10:19 AM

Not necessarily non-sequitur - the rose is the symbol of England, the leek is the symbol of Wales. But a rose with a trumpet? I'm lost there.

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#113
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 11:45 AM

Sorry that one didn't travel. Since Lloyd George, the Welsh have also used the daffodil as one of their many national symbols - possibly because in welsh the word 'Ceninen' means leek, and 'Ceninen Pedr' means daffodil. It's also more attractive (both visually and as regards odour) for use as a buttonhole on St. David's day.

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#109
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 10:45 AM

>"Is this thread spinning out of control?"

Apparently.

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#110
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Re: Spinning Wheel, Spinning True: Newsletter Challenge (05/08/07)

05/10/2007 11:18 AM

How can that be? Shouldn't it's angular momentum be keeping it on track? But I suppose one could argue, that once the discussion has been twisted in the vertical axis, there will be an effect in a perpendicular axis -- meaning that the conversation could go anywhere.

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