energy producing experiments

[greendoor]

I mean a simple out-of-balance wheel does not self rotate. In my youth I spent some time with a manual tyre balancing machine, hammering lead weights onto wheels to make them balance. I can assure you that an out-of-balance wheel does not self rotate, but it displays all the characteristics of the Atwood principle Pequaide has given us.

[nicbordeaux]

The only vid I found was this one http://s171.photobucket.com/albums/u290 ... roject.flv

But I did find a whole load of writing identical to what's up here and in other threads at a load of other places.

[pequaide]

The wheel is rotated (by hand) counterclockwise and the orange bag of BBs is released at about 5 o'clock. The longest throw is 32.5 m. A string goes all the way around the circumference of the wheel. The string has the BBs on one end and the other end is looped over the Allen wrench. All the motion can be transferred to the BB bag and the wheel can be stopped dead.


I believer that wheels like this one will prove that the Law of Conservation of Momentum will work for wheel trebuchets.

[nicbordeaux]

Nice one peq, but if you dump the driver mass in a more or less "haphazard fashion", you'll never work out the actual force given to the wheel and what the input/output ratios are. Still, agreed, if you dump mass, the flywheel mass will be free of the weight needed to get back to 12, and will produce some big throws, and it will be a straight demo of gravity moved flywheel transferring to flung mass.

What places are you aiming to take out ? Just pm me and maybe Fletcher, could be we have property in those places and might want to, you know, sell.

Edit: Hey pequiade, you have just ruined my coffee break, there I was having a fag and some good arbica, and an idea occurred to me : to get you drive weight constant and dumped, how about this : you have a second thin rim bolted to the one spooling the tether, and on this you tether a driver weight. If released from 12, it drives until it grounds. Then as it needn't be fixed in any way which is detrimental to performance, it is released. The weight applied is always constant from release point to 6.

[pequaide]

Let’s see: if the longest down range throw is 32.5 m then the bag a BBs must be going about 15 meters up. To go that high it must be moving about 20 m/sec (a little extra for air resistance). That 66g bag of BBs would have to have 1.32 units of momentum to achieve this height.

If a 2670g (I will guess about 2334g rotational inertia) rim mass wheel was wrapped with a string and a 66g mass was allowed to accelerate it as in an Atwood’s machine, it would have a velocity of 2.84 m/sec at the end of a 15 meter drop. That would be a momentum of 6.81, and we only need 1.32.

Yes; the haphazard release has to be avoided. A mechanical release also allows you to be absent from the vicinity of the release. What if the wheel has a mass twenty times as great and is moving 12 times as fast. Even now I can not visually pick up the motion of the bag until it is out about 15 meters. Of course I am concentrating on staying out of the way.

[pequaide]

I hope you don’t feel like I violated scientific etiquette but the 66 gram bag of BBs actually had a mass of 73.8 g. In the lab at home I don’t use an accurate scale; I have to take things to work to weigh them accurately.

At home I tied a 66 g mass on one end of a 1.47 m metal tube, on the other end I added BBs to a cloth bag until the tube balanced at the center. I can remember wanting to make this bag a little heavier than 66 gram so I balanced it about a cm off the center mark, which gave the 66 gram end a 2 cm longer lever arm. The actual mass of the bag was determined (with the use of a certified scale) when I got to work today. I knew that the bag had a mass of at least 66 grams so I hope you don’t think I was trying to deceive you. I like doing these experiments with unknowns, that way I record the data as is, because I don’t really know what data I am looking for. Then I weigh things later.

The 73.8 grams results are even better than 66 grams. I am throwing 73.8 grams 32.5 meters. This is 1/30 (73.8 /2400) the total mass instead of 1/36 (66/2400). This gives us a higher acceleration for the (envisioned) 15 meter Atwood’s (9.81/30). In fact you can reduce the assumed rise to 10 meters and still have way more velocity (after the 73.8 g accelerated the wheel 10 meters) than would be necessary to repeat the throw. This would be 2.55 m/sec for 6.12 units of momentum and you only need 1.42 units of momentum (for a rise of 20 meters) to repeat the experiment.
I am very comfortable believing that the BB bags rise over 10 meters. I have BB bags stuck in tree branches at about 13 meters; one of the bags was still rising when it hit the tree. It ricocheted around a little bit, fell back, and stuck in the branches.

[Fletcher]

Pequaide .. in case I missed it - how are you physically releasing the BB bag ? i.e. separating it from the string ? - & how is this timed for 5 o'cl to give the best trajectory for height & distance [32.5 m's horizontal distance achieved] - anybody trying to replicate something similar would probably like to know your release method.

Nick .. IINM a one-way clutch or ratchet would solve your drive apparatus problem i.e. a simple ratchet & pawl system between the two rims you suggest - the drive weight is hand positioned to 12 o'cl & drives downwards accelerating the secondary system - it is physically stopped at 6 o'cl & the mesh gears or pawls no longer engage [one-way bike hubs come to mind] - the BB bag also lends its OOB to aid the drive mechanism before release - you can now directly calculate how much Pe was lost & converted to Ke & empirically measure the acceleration of the BB bag upon release [or work backwards from height achieved] - if the BB bag is flung higher vertically than the Pe lost by a drive weight of similar mass [easy enough to adjust for Joules if dissimilar masses] then you have a winner & confirmation of pequiades theory - if the acceleration is insufficient then something is wrong with the arrangement or theory.

P.S. I'm in no way sceptical of the distances achieved by pequaides experiments but I too would like to know the input Joules by hand spinning to vertical height achieved Pe Joules of the BB bag for comparison sake.

[pequaide]

A balanced wheel accelerates according to F = ma, if the resulting momentum is not held by the BBs then Newtonian physics is false. I believe that Newtonian physics is true and that the BBs must have all the momentum.

I release the BBs by hand. I just keep doing it until I get them out there as far as they will go. I had two throws at 32 meters and one at 32.5 meters. I had a bunch between 27 and 30. The strangest ones are when the bag lands 10 or 15 meters out and I never saw the BBs in flight. I am thinking the bag is lost forever: and there it is; laying on the mowed part of the throw. At 27 meters you have foot high grass, you pretty much have to see it land.

[pequaide]

A balanced wheel accelerates according to F = ma, if the resulting momentum is not held by the BBs then Newtonian physics is false. I believe that Newtonian physics is true and that the BBs must have all the momentum.

I release the BBs by hand. I just keep doing it until I get them out there as far as they will go. I had two throws at 32 meters and one at 32.5 meters. I had a bunch between 27 and 30. The strangest ones are when the bag lands 10 or 15 meters out and I never saw the BBs in flight. I am thinking the bag is lost forever: and there it is; laying on the mowed part of the throw. At 27 meters you have foot high grass, you pretty much have to see it land.

[Fletcher]

I got it the first time ;7)

http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

Here is a link & page about trajectories from Hyper Physics web site for those interested.

Use the index far right to find trajectories [alphabetic] - have a read as it is generally very interesting with a bit of math by way of explanation.

Vertical height achieved rather than range is the most conclusive evidence as it can be directly translated to Pe & Ke gain or loss.

[nicbordeaux]

Nick .. IINM a one-way clutch or ratchet would solve your drive apparatus problem i.e. a simple ratchet & pawl system between the two rims you suggest - the drive weight is hand positioned to 12 o'cl & drives downwards accelerating the secondary system - it is physically stopped at 6 o'cl & the mesh gears or pawls no longer engage [one-way bike hubs come to mind] - the BB bag also lends its OOB to aid the drive mechanism before release - you can now directly calculate how much Pe was lost & converted to Ke & empirically measure the acceleration of the BB bag upon release [or work backwards from height achieved] - if the BB bag is flung higher vertically than the Pe lost by a drive weight of similar mass [easy enough to adjust for Joules if dissimilar masses] then you have a winner & confirmation of pequiades theory - if the acceleration is insufficient then something is wrong with the arrangement or theory.

Absolutely correct and nice thinking, a bike freewheel would suit nicely (repeatable behavior), but a good quality modern one (mayybe file the pawls down a bit), the old stuff tends to drag a bit too much. I'll leave that build/experiment to peq , not in the weight bunging game any more: just gave it a fling for fun :) Plus we now live less than 50 yards from a 12th century Abbey, I start throwing bowling balls at that, it's death row and they charge family for the bullet.

[pequaide]

Sorry about the double post, I thought it had not posted.

Let’s see: the 18 inch wheel throws a 66 gram bag 40 meters, the tether length is diameter times pi. The 16 inch wheel throws a 73.8 gram bag 32.5 meters and the tether length is diameter * pi. The bigger wheel also has a greater mass, which throws a lighter bag. Now we know that distance is the square of velocity, so we could probably calculate the velocity change.

But I got some gears in for the geared wheel, I think I will work on that.

Thanks for the ballistics I will take a look.

[pequaide]

My calculations show that the 66 gram bag is moving 11% faster (for the 40 m throw) than the 73.8 g bag (for the 32.5 m throw). The 66 grams is also 12% lighter. Maybe the rotational inertia of the two wheels is closer than I thought. The bigger wheel is a little above chest high which makes it harder to spin, and the 16 in. wheel is just right.



The square root of 40 / square root of 32.5 = 1.1094



73.8 g / 66 g = 1.118



This looks like Newtonian physics to me, the two momenta are almost identical. .066 kg *1.1094 = .07322 to 1 *.073.8 = .0738



The proximity of these numbers is probably a bit due to chance, but you can’t consistently get close unless you are sniffing down the right rabbit trail.

[greendoor]

Pequaide - you know that i'm a big fan of your work, but I have some problems with this experiment, which i'm sure will fuel the skeptics disapproval.

You say that a balanced flywheel is accelerated according to F = MA, i.e. A = F/M but the wheel you are describing is unbalanced, is it not? And does this make a difference anyway?

The use of manual energy input is going to confuse the issue no end, and the manual release will be looked upon skeptically. How high can you simply throw your bag of bb's with a single arm throw? Probably fairly high - our arms can generate some impressive peak energy when required.

I believe I understand what you are doing here ... you are spinning up the wheel and using it to store substantial energy. You can take your time to overcome the inertia of the wheel mass - and that means that the energy stored up in the wheel can be much higher than the energy of a short arm throw. So what we have here (to a skeptic) is simply a demonstration of a lot of human muscle energy being stored up over time and then applied to quickly throw a mass. The numbers are pretty much unknown, and this really is confusing your audience who are mostly skeptics.

I'm interested in your comment that the wheel can apply all it's momentum to the bag and come to a complete stop ... I find this hard to believe. If your wheel does indeed come to a complete stop, I suspect you are applying sufficient opposing force when you 'release' the bag ... it would be most interesting to see a video of what you do in slow motion.

This concept of a flywheel-based trebuchet is very interesting, but here is my problem with the concept: very obviously a flywheel can store energy. I know you prefer to consider this in terms of momentum, and afaik these are just two ways of crunching the same original numbers for mass and velocity. Albeit somewhat confusing because of the distinction made between angular and linear velocity. But we can at least agree that the flywheel has a fixed mass, and is rotating at a specific speed. The concentration of the mass means that the issue of Radius of Gyration is an important factor here to consider. I believe that if we know the Radius of Gyration, we can convert this amount of angular momentum into an equivalent amount of linear momentum.

For your energy-creating idea to have any merit, it is important that the flywheel can somehow deliver all (or most of ) it's momentum to the launched mass. Now I have a basic problem with this .... we know that IF we can impart momentum from a heavy mass to a light mass, the light mass accelerates faster and acquires a faster velocity. As soon as the lighter mass starts to move faster than the heavy mass - physical contact ceases, and therefore the impulse - the transfer of momentum - ceases. This is the reason that in Newton's Cradle with unequal mass, the heavy mass NEVER can impart all it's momentum to the lighter mass. The heavier mass just keeps on moving forward, at a slightly lower velocity depending on how much momentum was transfered in the brief amount of time that physical contact was available.

To transfer ALL the momentum from a heavy mass to a light mass will require something that maintains physical contact - such as a tether. By abandoning a tether in this experiment, i'm not sure what you are doing.

Does the wheel really stop? And if so, do you know why? This I believe to be the important part, and I'm not seeing how this could work. Maybe i'm just thick.

[greendoor]

Oops - I think I am thick. And fairly tired (it's way past my bedtime here). You DO have a tether. I can't really picture how this thing works, but maybe you are somehow using the tether to maintain the impulse while the bag accelerates? Do you allow the string to break? Or what? I'm just not getting it ...

EDIT: Does the string just slip off the allen key when it reaches the end?

The more I think about it, I think i'm starting to get it ... or if not, you've raised some very interesting thoughts for me to follow ...

Thanks :)