@Fletcher,
This sim is irrelevant. The correct sim (however, not using the flawed WM2D) must be based on the totality of all the torques created in the wheel at hand.
energy producing experiments
Moderator: scott
re: energy producing experiments
You miss the point again omnibus - it can be changed at will i.e. the 100 kg blue weights made to zero, then compared to the free fall example to test velocity's, mv & Ke - this is also under optimal conditions - this can be compared to the math predictions - additionally whilst it took half an hour to build a simplified sim one of the builders could probably knock up similar real world tests in a day or two.
The sim torque can be tested by applying a dampened spring element to the contraptions & comparing the compression/extension - this is effectively the same as a prony brake that could also be applied to any real builds to measure torque at any angle.
If there were to be a big difference in outputs between sim & real build then the investigation would need to proceed further by adding in simulated real world losses, or finding another explanation for the difference - it might be that the sim is flawed or it could be that pequiade & greendoor were correct all along.
The sim torque can be tested by applying a dampened spring element to the contraptions & comparing the compression/extension - this is effectively the same as a prony brake that could also be applied to any real builds to measure torque at any angle.
If there were to be a big difference in outputs between sim & real build then the investigation would need to proceed further by adding in simulated real world losses, or finding another explanation for the difference - it might be that the sim is flawed or it could be that pequiade & greendoor were correct all along.
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Wubbly
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re: energy producing experiments
Pequaid and Greendoor, I have to admit that I may have been wrong with my momentum analysis ...
I spent several hours searching through a physics book and I found an Atwoods example.
In this example the Atwoods machine has two masses (m1 and m2) and a pully (with radius R and moment of inertia I).
It asks to find the acceleration of the masses, and the Angular Acceleration of the pully.
During the solution, it needs to calculate angular momentum of the pully to solve the problem, so you have to believe in angular momentum.
The physics book defines angular momentum "L" as the vector cross product of the position vector r and the linear momentum p.
A previous example in the physics book solves the angular momentum of a particle, relative to the origin, and moving on a line parallel to the x axis.
The atwoods example uses the solution to this and adds to it.
In the Atwoods example it took the absolute value of V1, the absolute value of V2, and said that was V.
(I don't understand how you can "push" on a string, but in the example, it looks like the upward velocity of M1 is adding to the angular momentum of the pully,
and the downward velocity of M2 is adding to the angular momentum of the pully.)
It then wrote the equation for the angular momentum of the pulley as:
L = (M1 * V * R) + (M2 * V * R) + Iw
It then said V = R * w
w = V / R
and eliminating w out of the equation
L = (M1 * V * R) + (M2 * V * R) + I * V / R
and simplified
L = (M1 + M2) * V * R + ( I * V / R)
This was an intermediate step in the example, and it then went on to solve what the problem was asking.
... If the pully is massless, "I" would be zero, and we are left with something very similar to what you guys were saying all along.
L = (M1 + M2) * V * R
But this equation has R, (the radius of the pully), in it, and it is Angular momentum.
If you set R = 1m, then the equation becomes what you guys have been saying, except it's angular momentum.
The example totally blew my mind, but there it was in a physics text book.
If the angular momentum of the pully can be translated back into linear momentum, then perhaps my momentum analysis was a little too simple minded.
I spent several hours searching through a physics book and I found an Atwoods example.
In this example the Atwoods machine has two masses (m1 and m2) and a pully (with radius R and moment of inertia I).
It asks to find the acceleration of the masses, and the Angular Acceleration of the pully.
During the solution, it needs to calculate angular momentum of the pully to solve the problem, so you have to believe in angular momentum.
The physics book defines angular momentum "L" as the vector cross product of the position vector r and the linear momentum p.
A previous example in the physics book solves the angular momentum of a particle, relative to the origin, and moving on a line parallel to the x axis.
The atwoods example uses the solution to this and adds to it.
In the Atwoods example it took the absolute value of V1, the absolute value of V2, and said that was V.
(I don't understand how you can "push" on a string, but in the example, it looks like the upward velocity of M1 is adding to the angular momentum of the pully,
and the downward velocity of M2 is adding to the angular momentum of the pully.)
It then wrote the equation for the angular momentum of the pulley as:
L = (M1 * V * R) + (M2 * V * R) + Iw
It then said V = R * w
w = V / R
and eliminating w out of the equation
L = (M1 * V * R) + (M2 * V * R) + I * V / R
and simplified
L = (M1 + M2) * V * R + ( I * V / R)
This was an intermediate step in the example, and it then went on to solve what the problem was asking.
... If the pully is massless, "I" would be zero, and we are left with something very similar to what you guys were saying all along.
L = (M1 + M2) * V * R
But this equation has R, (the radius of the pully), in it, and it is Angular momentum.
If you set R = 1m, then the equation becomes what you guys have been saying, except it's angular momentum.
The example totally blew my mind, but there it was in a physics text book.
If the angular momentum of the pully can be translated back into linear momentum, then perhaps my momentum analysis was a little too simple minded.
re: energy producing experiments
Because without the tension on the string from both masses the pulley won't turn.I don't understand how you can "push" on a string, but in the example, it looks like the upward velocity of M1 is adding to the angular momentum of the pully,
and the downward velocity of M2 is adding to the angular momentum of the pully
meChANical Man.
--------------------
"All things move according to the whims of the great magnet"; Hunter S. Thompson.
--------------------
"All things move according to the whims of the great magnet"; Hunter S. Thompson.
re: energy producing experiments
Greendoor quotes:
A - we use heavy balanced weights to accumulate momentum by virtue of a small overbalance weight.
B - the accumulated momentum is relatively slow (compared to freefall) but massive (compared to the small overbalance weight). This momentum needs to be transfered to the small overbalance weight. If this can be done successfully with minimal losses, the result should be a large increase in velocity (because Momentum is conserved).
I propose a similar experiment to prove/disprove this theory - which I shall call "Pequaide A".
Set up a very large balanced see-saw. Have 1000 kg masses on each end. Let's imagine the see-saw can fall, say, 2 meters. Lie with your head underneath one of the 1000 kg weights. It's as light as a feather, because it is perfectly balanced by the opposite 1000 kg weight.
OK so far?
Now - for the experiment control, let's take a box of Cornflakes. Let's drop the box of Cornflakes from 2 meters, right onto your face. I think most of us are tough enough to withstand a full frontal assault from a box of Cornflakes dropped flatside onto our face.
OK?
Now - place your face underneath the 1000 kg mass at one end of the see-saw. Raise the see-saw so this mass is now 2 meters above your face. Place the box of cornflakes on this see-saw.
You will see the 1000 kg weight slowly - very slowly - start to accelerate. It gets faster and faster - you can see it accelerating ...
Do you pull you face away, and run away like a chicken?
Or do you let the 1000 kg weight smack you in the face?
Remember - it's fully balanced, and effectively weightless ...
But it has momentum - a lot of momentum by my calculations ...
Who do you trust? Michael, Broli & Fletcher? Would you leave your face underneath it?
Personally - I wouldn't. I value my head too much.
Pequaide.:
Note that Greendoor calls this see-saw thought experiment “Pequaide A� meaning step A: of the previous statement. This means that if your face survives step A we have step B waiting for you. Do you still have your pocket book out?
Step A: I just grabbed a box of Kellog’s corn flakes: It has a mass of 18 ounces, .510 kg.
Dropped two meter in freefall the box of corn flakes will have (d = ½ v²/a) and (Ke = ½ mv²) 10 joules of energy.
The 2000 kg see-saw with the corn flakes on one end will have an acceleration of .510/2000.510 * 9.81 = .0025 m/sec/sec. at the end of a two meter drop it will have a velocity of .1000 m/sec, which will give it 10.00 joules of energy.
Now a soft box of corn flakes seem friendlier to the face than a board, but let us be fair 10 joules is 10 joules. Let’s be even fairer and change the corn flakes into a .510 kg steel sphere. Now: neither one of us wants to get hit with either one. But let’s revise the two previous paragraphs.
Dropped two meter in freefall the .510 kg steel sphere will have (d = ½ v²/a) and (Ke = ½ mv²) 10 joules of energy, 6.264 m/sec velocity and 3.194 units of momentum.
The 2000 kg see-saw with the .510 kg steel sphere on one end will have an acceleration of .510/2000.510 * 9.81 = .0025 m/sec/sec. At the end of a two meter drop it will have a velocity of .1000 m/sec, which will give it 10.00 joules of energy, and 200.051 units of momentum.
So now we go to step B: we transfer all the momentum of the see-saw into the .510 kg sphere. For the sphere to comply with Newton’s Three Laws of Motion it will have to be moving 393.15 m/sec. Oh: and the energy is the square of the velocity, at 39,414.56 joules.
You don’t mind if we add step B; do you Michael?
Kepler’s angular momentum conservation works in space with gravity on, not in the lab with gravity off. See previous posts.
A - we use heavy balanced weights to accumulate momentum by virtue of a small overbalance weight.
B - the accumulated momentum is relatively slow (compared to freefall) but massive (compared to the small overbalance weight). This momentum needs to be transfered to the small overbalance weight. If this can be done successfully with minimal losses, the result should be a large increase in velocity (because Momentum is conserved).
I propose a similar experiment to prove/disprove this theory - which I shall call "Pequaide A".
Set up a very large balanced see-saw. Have 1000 kg masses on each end. Let's imagine the see-saw can fall, say, 2 meters. Lie with your head underneath one of the 1000 kg weights. It's as light as a feather, because it is perfectly balanced by the opposite 1000 kg weight.
OK so far?
Now - for the experiment control, let's take a box of Cornflakes. Let's drop the box of Cornflakes from 2 meters, right onto your face. I think most of us are tough enough to withstand a full frontal assault from a box of Cornflakes dropped flatside onto our face.
OK?
Now - place your face underneath the 1000 kg mass at one end of the see-saw. Raise the see-saw so this mass is now 2 meters above your face. Place the box of cornflakes on this see-saw.
You will see the 1000 kg weight slowly - very slowly - start to accelerate. It gets faster and faster - you can see it accelerating ...
Do you pull you face away, and run away like a chicken?
Or do you let the 1000 kg weight smack you in the face?
Remember - it's fully balanced, and effectively weightless ...
But it has momentum - a lot of momentum by my calculations ...
Who do you trust? Michael, Broli & Fletcher? Would you leave your face underneath it?
Personally - I wouldn't. I value my head too much.
Pequaide.:
Note that Greendoor calls this see-saw thought experiment “Pequaide A� meaning step A: of the previous statement. This means that if your face survives step A we have step B waiting for you. Do you still have your pocket book out?
Step A: I just grabbed a box of Kellog’s corn flakes: It has a mass of 18 ounces, .510 kg.
Dropped two meter in freefall the box of corn flakes will have (d = ½ v²/a) and (Ke = ½ mv²) 10 joules of energy.
The 2000 kg see-saw with the corn flakes on one end will have an acceleration of .510/2000.510 * 9.81 = .0025 m/sec/sec. at the end of a two meter drop it will have a velocity of .1000 m/sec, which will give it 10.00 joules of energy.
Now a soft box of corn flakes seem friendlier to the face than a board, but let us be fair 10 joules is 10 joules. Let’s be even fairer and change the corn flakes into a .510 kg steel sphere. Now: neither one of us wants to get hit with either one. But let’s revise the two previous paragraphs.
Dropped two meter in freefall the .510 kg steel sphere will have (d = ½ v²/a) and (Ke = ½ mv²) 10 joules of energy, 6.264 m/sec velocity and 3.194 units of momentum.
The 2000 kg see-saw with the .510 kg steel sphere on one end will have an acceleration of .510/2000.510 * 9.81 = .0025 m/sec/sec. At the end of a two meter drop it will have a velocity of .1000 m/sec, which will give it 10.00 joules of energy, and 200.051 units of momentum.
So now we go to step B: we transfer all the momentum of the see-saw into the .510 kg sphere. For the sphere to comply with Newton’s Three Laws of Motion it will have to be moving 393.15 m/sec. Oh: and the energy is the square of the velocity, at 39,414.56 joules.
You don’t mind if we add step B; do you Michael?
Kepler’s angular momentum conservation works in space with gravity on, not in the lab with gravity off. See previous posts.
re: energy producing experiments
The components of the cylinder and spheres machine, or a disk and pucks on a frictionless plane, do not have gravitational pulls between them like the Sun and a comet. Kepler’s angular momentum works for comets it does not work in the lab.
re: energy producing experiments
Thanks for your patience and academic diligence Pequaide.
I appreciate the points about the relevance of angular momentum. It's very easy to assume that just because a component is rotating that we have to use angular momentum calculations. Because we are mainly interested in the Horizontal displacement, the Vertical displacement isn't our main concern. As Fletcher pointed out - a mass falling down a curved path seems to acquire the same velocity (hence energy) anyway - it just takes a little more time than straight down.
The pulley-type Atwood machine isn't the best for a practical machine. Mainly for the reason Wubbly pointed out: a string can only be tensioned one way. (@Michael - I accept your point - decreasing tension is still tension, but we really want to decelerate the whole system to zero, and grab all the momentum possible out of both masses. A string is no good for this.)
I suggested the see-saw example more for the visual mind picture. A pivoted beam such as Fletcher has drawn would be another solution.
These machines are sort of halfway between linear and rotary. It shouldn't worry us too much whether we use angular momentum calculations, or linear kinetic motion equations. For practical purposes, simple linear equations should be in the ballpark. Close enough for rock-n-roll.
Just think that a revolving mass will take off on a linear tangent with just the same momentum that it had prior to disconnecting - so in real physical terms, it's not a black & white situation. Common sense indicates that there isn't such a huge difference between linear & rotary motion that the equations are going to be miles off. There's not much difference between a straight line & a really big circle anyway.
Sorry if this upsets anyone - i'm just trying to address this black & white mentality that angular momentum calculations MUST be used for rotating or semi-rotating systems. The universe will not implode if we use the simple linear equations as an approximation. That's all these laws are anyway - reasonable approximations of much more complex particle systems.
I appreciate the points about the relevance of angular momentum. It's very easy to assume that just because a component is rotating that we have to use angular momentum calculations. Because we are mainly interested in the Horizontal displacement, the Vertical displacement isn't our main concern. As Fletcher pointed out - a mass falling down a curved path seems to acquire the same velocity (hence energy) anyway - it just takes a little more time than straight down.
The pulley-type Atwood machine isn't the best for a practical machine. Mainly for the reason Wubbly pointed out: a string can only be tensioned one way. (@Michael - I accept your point - decreasing tension is still tension, but we really want to decelerate the whole system to zero, and grab all the momentum possible out of both masses. A string is no good for this.)
I suggested the see-saw example more for the visual mind picture. A pivoted beam such as Fletcher has drawn would be another solution.
These machines are sort of halfway between linear and rotary. It shouldn't worry us too much whether we use angular momentum calculations, or linear kinetic motion equations. For practical purposes, simple linear equations should be in the ballpark. Close enough for rock-n-roll.
Just think that a revolving mass will take off on a linear tangent with just the same momentum that it had prior to disconnecting - so in real physical terms, it's not a black & white situation. Common sense indicates that there isn't such a huge difference between linear & rotary motion that the equations are going to be miles off. There's not much difference between a straight line & a really big circle anyway.
Sorry if this upsets anyone - i'm just trying to address this black & white mentality that angular momentum calculations MUST be used for rotating or semi-rotating systems. The universe will not implode if we use the simple linear equations as an approximation. That's all these laws are anyway - reasonable approximations of much more complex particle systems.
Anything not related to elephants is irrelephant.
re: energy producing experiments
@Wubbly’s is giving an example of how a discussion should be conducted and what scientific arguments really look like. @pequaide and @greendoor will benefit greatly if they read more carefully what @Wubbly is writing and what he’s trying to tell them rather than continue to splash their confusion further in lengthy postings. In addition to the good arguments he's presenting, @Wubbly has also accepted an approach to put himself in the shoes of a confused novice and bring down the problem and its analysis to the rudimentary level some people here are up to. Obviously, @Wobbly isn’t just an expert in this field but is also a good pedagogue.
re: energy producing experiments
@pequaide and @greendoor,
Focus on this:
Focus on this:
@Wubbly is giving you a chance to show his momentum analysis was a little simple minded. Show how the angular momentum of the pulley can be translated back into linear momentum.If the angular momentum of the pully can be translated back into linear momentum, then perhaps my momentum analysis was a little too simple minded.
re: energy producing experiments
My cornflake Gedankenexperiment was a little hasty and probably not lethal. FWIW - these are my rough numbers:
0.5 kg Cornflake box dropped 2 meters:
Final Velocity = 6.26 m/s
Time = 0.64 s
Final Momentum = 3.13 kg*m/s
0.5 kg Cornflake box dropped 2 meters used to accelerate a see-saw balancing 2 x 1000 kg:
F = MA <=> A = F/M
A = 9.81/2001 = 0.0049 m/s/s
V^2 = 2AD
V^2 = 2*0.0049*2 = 0.0196
Final Velocity = 0.14 m/s
Time = 28.57 s
Final Momentum = 280.14 kg*m/s
Notice that I don't bother doing the energy calculations, because I have been trying to make the case that 0.5MV^2 is a mathematical tool that is useful for comparing certain things against freefalling objects. But note that it cannot be an actual representation of the physical reality of motion. Because no object can move at V^2. It's an accounting game - and it is biased strongly to favour velocity over mass. Is that fair for all cases of motion?????
Seems to me that we have developed an exponential-scaled ruler, and attempt to measure everything with this, and maybe it isn't always the best tool for the job??
So please - for one moment - forget about energy. Maybe the energy calculations will show that the energy numbers are the same.
Can I stop for one moment to mention the elephant in the room?
Look at the Momentum difference. 3.13 kg*m/s vs 280.14 kg*m/s.
Is this really a trivial difference we can simply discard? Think about Newtons Cradle - and the Conservation of Momentum.
I would be happy to be hit on the head with a box of cornflakes, dropped 2 metres in 0.64 seconds, acquiring momentum of 3.13 kg*m/s.
I would definately not be happy to insert my head between a rock and a hard place if that rock was the combined momentum of two 1000 kg masses, that have been continually accelerating for 28.57 seconds, and have acquired momentum of 280.14 kg*m/s.
That is a difference in Momentum of approx 89 times! Of course the velocity is much slower (approx 44 times slower). But when it comes to head crushing ability - is speed an advantage?
Maybe i've crunched these numbers wrong - i'm in a bit of a hurry. Please feel free to check everything for yourself.
The issue - as I see it. We've been brainwashed to value Energy over Momentum. Does this match real world?? The "thump" that I see as my heavy masses pound into the ground is suggesting that momentum increase is palpable. I need more work, and I really should STFU until i've done the builds. But then, maybe I wouldn't want to share.
I just want to let you know that despite the bullshit - I have given this serious thought, and I sometimes wonder if my critics have given any thought at all before dismissing what i'm trying to say.
For what it's worth. Full credit to Pequaide for giving us this gift.
@ Pequaide - it's no wonder your ideas have not been as enthusiastically received as they should be. Most people have stumbled over the very first hurdle. I'm still trying to prove "Pequaide A" - we haven't even started on "Pequaide B" yet ...
0.5 kg Cornflake box dropped 2 meters:
Final Velocity = 6.26 m/s
Time = 0.64 s
Final Momentum = 3.13 kg*m/s
0.5 kg Cornflake box dropped 2 meters used to accelerate a see-saw balancing 2 x 1000 kg:
F = MA <=> A = F/M
A = 9.81/2001 = 0.0049 m/s/s
V^2 = 2AD
V^2 = 2*0.0049*2 = 0.0196
Final Velocity = 0.14 m/s
Time = 28.57 s
Final Momentum = 280.14 kg*m/s
Notice that I don't bother doing the energy calculations, because I have been trying to make the case that 0.5MV^2 is a mathematical tool that is useful for comparing certain things against freefalling objects. But note that it cannot be an actual representation of the physical reality of motion. Because no object can move at V^2. It's an accounting game - and it is biased strongly to favour velocity over mass. Is that fair for all cases of motion?????
Seems to me that we have developed an exponential-scaled ruler, and attempt to measure everything with this, and maybe it isn't always the best tool for the job??
So please - for one moment - forget about energy. Maybe the energy calculations will show that the energy numbers are the same.
Can I stop for one moment to mention the elephant in the room?
Look at the Momentum difference. 3.13 kg*m/s vs 280.14 kg*m/s.
Is this really a trivial difference we can simply discard? Think about Newtons Cradle - and the Conservation of Momentum.
I would be happy to be hit on the head with a box of cornflakes, dropped 2 metres in 0.64 seconds, acquiring momentum of 3.13 kg*m/s.
I would definately not be happy to insert my head between a rock and a hard place if that rock was the combined momentum of two 1000 kg masses, that have been continually accelerating for 28.57 seconds, and have acquired momentum of 280.14 kg*m/s.
That is a difference in Momentum of approx 89 times! Of course the velocity is much slower (approx 44 times slower). But when it comes to head crushing ability - is speed an advantage?
Maybe i've crunched these numbers wrong - i'm in a bit of a hurry. Please feel free to check everything for yourself.
The issue - as I see it. We've been brainwashed to value Energy over Momentum. Does this match real world?? The "thump" that I see as my heavy masses pound into the ground is suggesting that momentum increase is palpable. I need more work, and I really should STFU until i've done the builds. But then, maybe I wouldn't want to share.
I just want to let you know that despite the bullshit - I have given this serious thought, and I sometimes wonder if my critics have given any thought at all before dismissing what i'm trying to say.
For what it's worth. Full credit to Pequaide for giving us this gift.
@ Pequaide - it's no wonder your ideas have not been as enthusiastically received as they should be. Most people have stumbled over the very first hurdle. I'm still trying to prove "Pequaide A" - we haven't even started on "Pequaide B" yet ...
Anything not related to elephants is irrelephant.
Re: re: energy producing experiments
Wubbly is cool. If you read what i'm saying, I am listening to him and addressing his concerns. Maybe not to your satisfaction - but I don't know what would satisfy you. I think you are here to disrupt and derail and spread disinformation. How much are they paying you?Omnibus wrote:@Wubbly’s is giving an example of how a discussion should be conducted and what scientific arguments really look like. @pequaide and @greendoor will benefit greatly if they read more carefully what @Wubbly is writing and what he’s trying to tell them rather than continue to splash their confusion further in lengthy postings. In addition to the good arguments he's presenting, @Wubbly has also accepted an approach to put himself in the shoes of a confused novice and bring down the problem and its analysis to the rudimentary level some people here are up to. Obviously, @Wobbly isn’t just an expert in this field but is also a good pedagogue.
I don't know what you are afraid of. Real world experiments will confirm or destroy this theory we are discussing. Nothing else.
Anything not related to elephants is irrelephant.
re: energy producing experiments
Wubbly: construct an Atwood’s string with 51 kg on one side and 50 kg on the other side. Now place the string and masses on two different size pulleys (both have very little mass and are frictionless). Does the Atwood’s behave differently because the one pulley has a radius of .10 meters and the other has a radius of .25 meters?
You probably will not find this experiment in the literature, but you will find the experiment in my lab. Take my word for it, pulley diameter has nothing to do with an Atwood’s. I have several Atwood’s with different radii and they all behave alike, F = ma.
You probably will not find this experiment in the literature, but you will find the experiment in my lab. Take my word for it, pulley diameter has nothing to do with an Atwood’s. I have several Atwood’s with different radii and they all behave alike, F = ma.
re: energy producing experiments
@greendoor,
Read carefully what @Wubbly writes and make an effort to understand it. Your ramblings on other issues are beside the point.
Read carefully what @Wubbly writes and make an effort to understand it. Your ramblings on other issues are beside the point.
Re: re: energy producing experiments
This sim is indeed interesting. Besides the delay in circular motion you show I discovered something else in the parallelogram setup.Fletcher wrote:Broli .. here is [what I think] an interesting see-saw comparison you might want to consider [try changing the values of components ?]
I moved the yellow weight slightly to the left and now it ends up rising higher than the initial position while the net potential energy of the heavy blocks is 0.
Is this some accidental discovery of something useful?
Edit:Looks like I was a bit too hasty as increasing the accuracy removes this behavior.
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re: energy producing experiments
Ah well.
meChANical Man.
--------------------
"All things move according to the whims of the great magnet"; Hunter S. Thompson.
--------------------
"All things move according to the whims of the great magnet"; Hunter S. Thompson.