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Question

Asked by: Blaze
Subject: For those who still think spinning mass has no momentum.
Question: I get the impression (maybe incorrectly) that some people still think that spinning mass has no momentum. Here is a simple experiment that you can do to prove that spinning mass does indeed have momentum and it has the same momentum as non spinning mass. I have actually done a simple version of this experiment as a kid, and would say that most farm kids probably have as well.

Imagine a semi truck tire (20 or 22 inch solid rim) that detaches from a truck moving at 100 kilometers per hour. The tire and rim is probably somewhere between 50 and 100 pounds. If you have ever seen this happen it is truly a scary site. Imagine trying to stop this with your body. If spinning matter had no momentum then you wouldn’t have any problem stopping this tire suddenly and would feel little if any force. Please don’t actually try this. It will kill you.

Another way of doing this is to let a car tire with rim or a truck tire with the rim roll down a children’s playground slide. Rolling down the slide will get the tire up to a fairly good speed. Shortly after it leaves the slide and is rolling across the ground, try to stop it suddenly with your body. Again if spinning matter had no momentum then you wouldn’t have any problem stopping this tire suddenly and would feel little if any force but of course you will feel a significant amount of force. This experiment you will likely survive but don’t come complaining to me if you get hurt.

For those of you who say that a gyro is precessing and the tire isn’t, that is why the precessing gyro doesn’t have momentum, then try this. Roll a tire with the rim along the ground or pavement QUICKLY (especially with the type of rim where most of the metal is not in the center but rather is near the outside of the tire). You will find that this tire/rim combo will want to roll in a large circle because the center of mass is not in the center of the tire which means the tire/rim combo is “precessing” just like an overhung gyro but without the axle or pivot. Try to stop the “precessing” tire/rim combo suddenly. Again if spinning matter had no momentum then you wouldn’t have any problem stopping this tire suddenly and would feel little if any force and again you will feel a significant amount of force.

The experiment done as a kid was simply rolling a tire along the ground and trying to stop it suddenly. I learned really quickly that it takes significant force to stop mass, it makes no difference if it is spinning or not spinning.

regards,
Blaze
Date: 6 April 2014
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Answers (Ordered by Date)


Answer: Blaze - 06/04/2014 17:33:21
 "(especially with the type of rim where most of the metal is not in the center but rather is near the outside of the tire)"

should read
(especially with the type of rim where most of the metal is not in the centered between the sidewalls but rather is near or lined up with one of the sidewalls of the tire)

Blaze

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Answer: Sandy Kidd - 06/04/2014 21:00:24
 Hello all still interested;
To Blaze I have to say that the guys who are arguing with you were once upon a time like yourself and believed what you at present believe.
Now we are known as idiots because we have learned that there are alternatives to the establishment view but as for being idiots we at least are self-made men.
However each experiment you used as proof is debatable and can be interpreted in favour of the view from either side of the fence.
To my mind they are not conclusive enough to end the argument.

I do agree with most of your observations about the wheel and tyre
I really do not know why you thought any of us were claiming loss of angular momentum just because the item was spinning.
I have seen the result of a flywheel detaching itself from the front of my 1750 cc Maxi engine and am under no illusions on that front.
Unless the rotating disc wheel whatever is subjected to at least two other accelerations there will be no change in the angular momentum.

This is easily proved.
To lose angular momentum the disc whatever must be accelerated firstly around itself on a short shaft or similar, just like a car wheel, but it must also be accelerated in a circle at right angles to its rotation on that shaft, the non-disc end of the shaft being anchored at a fulcrum point such that the disc and shaft can be rotated around it.
This action causes the disc to accelerate upwards at right angles to the plane of disc and shaft rotation. This is often wrongly called precession.
This loss of angular momentum will not be seen until it has all gone at the point I call the “saturation point”, when the disc will be able to accelerate inwards and upwards due to the torque of the disc.
Depending on the rotation speed of the disc, angular momentum will be progressively shed up to a point where there is none left in the movement.
Of course juggling with the rotation speed of the disc and shaft can also cause changes in angular momentum.
If the disc and shaft are rotating clockwise when viewed from above the disc rotation must also be in a clockwise direction when viewed as the face of the disc passes you.
Health warning. Do not attempt this with a single gyro or flywheel system, as the lack of balance and forces involved could easily kill you.
Regards,
Sandy
PS
Please do not say I must be mistaken, as I have been doing this experiment on and off for the best part of 30 years.
I had a posting prepared for Momentus relating to the hidden attributes of flywheels in mechanically accelerated systems, seems like I should send it.


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Answer: Harry K. - 07/04/2014 14:22:03
 Hello Blaze,

I believe that you mean the existence of angular momentum in precession movement but not in spinning movement because I think there is nobody here in the forum who would deny the existence of angular momentum in spinning mass.

That there is stored angular momentum in precession movement, mainly in gravity driven gyroscopes is no novelty brought up by yourself. Long time before you joined this forum we discussed this issue although some contributors did not agreed wit that.
However, you have proved it by experiment und thus we (at least me) are thankful for your good job!

One hint, based on own experiences: you should not underrate any of the guys here in the forum! Each guy has its own way of thinking and thus it makes it very difficult to claim what is true and wrong.

For instance, I categorical refused Sandys claim about the existence of what he called a “saturation zone” over a long time. Now, after many hours of thinking over the edge of a plate (what is difficult for me), I’m convinced now that he could be right. I have new ideas about a possible cause of the effect of loosing angular momentum under certain conditions but I will first discuss these ideas directly with Sandy.

I’m afraid that movements and behavior of an accelerated gyro / flywheel system are much more complicated than you may imagine!

Anyway, I wish you much success with your own ideas!

Regards,
Harald


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Answer: Glenn Hawkins - 07/04/2014 15:13:39
 Good post, Harry.
I was thinking along the same lines about a saturation zone, but it is like opening up a can of worms isn't it? I have written about it a few times and then deleted the writing. I'm not ready.
Regards
Glenn

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Answer: Blaze - 08/04/2014 01:56:08
 Hi Harry and all. I did not mean or intend to underrate anyone on the forum, sorry if it came across that way.

Blaze

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Answer: Blaze - 13/04/2014 03:30:49
 Maybe everyone knows what I am about to write and at the risk of insulting everyone’s intelligence (not my intent), I will write it anyway.

So everyone agrees that spinning mass has momentum. Some of you picked up the point that I was trying to make was not about spinning mass moving in a straight line but rather that spinning mass moving in a circle still has full momentum, thus the last example of a tire and rim rolling quickly in a circle. I think we probably all agree that full momentum exists in this case.

So what keeps the tire/rim from falling on its side while rolling in a circle? (It is weighted to one of the sidewalls by the lopsided mass of the rim and thus wants to fall on its side). As you probably all know it is the balance between centrifugal force and gravity. Gravity is trying to make it fall on its side due to the lopsided weighting of the rim. Centrifugal force from rolling in a circle is balancing the pull of gravity and keeping the tire/rim up. In this scenario you don’t need anything (rope, rod, etc) between the post at the center point of the circle and the tire/rim to keep it rolling in a circle because the tire/rim is tilted to one side by the lopsided weight distribution of the rim.

If the tire/rim were rolling straight (not in a circle) then you would need a rope or rod or something attached to the tire/rim (balanced weighting of the rim mass in this scenario, not lopsided) and the post at the center of the circle if you want the tire/rim to actually roll in a circle. The tire/rim is still rolling on the ground in this scenario. Even though the tire/rim is perfectly upright (not tilted) it would experience centrifugal force because it has momentum as it is rolling along the ground and because it is being pulled into a circle by the rope or rod which is attached to the tire/rim and the post at the center of the circle. This scenario is in effect the same as if the tire/rim were tilted and rolling in a circle without any rope or rod attaching it to the center of the circle except that centripetal force replaces gravity.

Now take it one step further (and this is where I will lose some of you). Extend the length of the post upwards. Attach the rod to the top of the post and to the tire/rim. Allow the rod vertical and horizontal movement at the post. With the tire/rim spinning at the same speed as if it were rolling along the ground and the rod pivoting horizontally on the post at the same speed as when the tire was rolling in a circle in the previous scenario, we have the same thing as the previous scenario, except that the whole thing is now circling in the air (no longer rolling along the ground). That is one big gyro. Full momentum and full centrifugal force still exists because the spin rate of the tire/rim hasn’t changed and the horizontal rotation of the rod around the post (attached to the tire/rim) is still the same speed as when the tire/rim was rolling along the ground. If the tire/rim had momentum rolling in a circle, then it has momentum when precessing in a circle like in this last scenario.

Now, maybe everybody already knows this and I am just wasting time and ink, but I got the impression (maybe mistakenly) that some people don’t. I am not trying to get under anyone’s skin, just trying to make a point.

Regards,
Blaze


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Answer: Blaze - 13/04/2014 03:37:21
 "If the tire/rim had momentum rolling in a circle, then it has momentum when precessing in a circle like in this last scenario."

should be:

"If the tire/rim had momentum and centrifugal force rolling in a circle, then it has momentum and centrifugal force when precessing in a circle like in this last scenario.

Blaze

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