@iLOVENATURE2011 Hahah, probably not. This is a pretty old design and the efficiency is awful. I think it only survives as a neat little demonstration of how simple the thermodynamic idea of an engine can be.
@iLOVENATURE2011 haha two heat lamps at probably 200W each putting about (SWAG) 2W into spinning wheel... 0.5% efficiency. Heat engines have something to provide, no doubt, but this experiment is more in the "gee whiz" category than the future of energy conversion category.
1:02 You say that when rubber bands expand when they get hot, this is not true - they shrink. This is demonstrated by the center of mass shifting away from the heat source 1:57.
@AtomicLibido At 0:59 I say "what you would think is going to happen...", and the point is that I'm trying to demonstrate that the system runs in a counterintuitive manner.
Cripes, if I had $50 for every 'smart cookie' who watches half this video and thinks its cool to call me on a mistake that actually isn't a mistake (its a deliberate attempt to point out that things aren't always what you expect in science), I would have my own multimillion $ studio and competing with mythbusters... sheesh!
@sug15 Yeah you could. It's hard to say how much of a boost it would give you, probably not insignificant, but I also wouldn't say that its so radical that you suddenly have something that's anything more than a curiosity.
Neat video! I am doing this project for thermo class now. Can you please inform me of any calculations that may be useful in explaining work, energy and heat loss? The energy which i think is elastic potential is most confusiing to me. Please help. Thanks
Hi, I am a student currently taking physics in high school and I used your video to make this engine to show in my class. I had no trouble cutting and bending the spokes and stringing the rubber bands but I'm having difficulty shifting the center of mass to the middle of the wheel, where it's supposed to be. I have tried rebending the spokes, but it isn't helping. How did you fix this problem?
@ETG0818 The easiest way is to weight up the wheel. So ours has a strip of metal that runs inside the tire groove. When we first made it, we removed metal from this to get the mass into the right place. But the balance shifts often as you replace the rubber bands, because they all have slightly different tensions, etc. So we now balance the wheel as they do on cars, by adding weight opposite to the side that falls under gravity. I use blue-tack for this (its much like plasticine).
@ETG0818 Just set the wheel in some position and watch it rotate to where it stops, the heaviest bit will then be at the bottom, so add mass to the top of the wheel. Repeat many times until whenever you set the wheel, irrespective of where it is in its rotation, it doesn't move any more. Then its balanced. Takes a lot of adding and removing mass, and can be a good 30-60 minutes worth of work to get it right. (But there's always a lot of set up time invested in a good science demo ;) )
Ahhh, ok, I'm going to make you be more precise if you're going to make accusations of wrong. I give two explanations in the video. In the first, the heated side rotates downward (i.e., clockwise) because the bands expand. This is the naive expectation. It really goes the other way (i.e. anticlockwise) because rubber bands contract when heated. I believe this is quite clear (my students got it, so did many other viewers).
OK, two questions then. How does the tension increase without a material contracting unless the material is held at a fixed length by some mechanism (and its not in this case)? And second, if there IS no contraction of the rubber band, then how do you explain the shift in the center of mass of the wheel that makes it rotate.
Your answer here doesn't agree with textbook knowledge of mechanics.
"How does the tension increase without a material contracting unless the material is held at a fixed length by some mechanism (and its not in this case)?"
If you heat a gas confined in a vessel of constant volume does its pressure not increase?
Yes, if I heat a gas at constant volume, the pressure rises. But there are two problems now. First, a rubber band is not a gas, its a solid, and in solids potential energy is everything, in a gas its mostly kinetic. Second, if you translate the analogy across, my rubber band is not at fixed volume. Like I said, there is nothing stopping the rubber band changing its length. The correct analogy would be a gas in a rubber balloon, and then if I heat it, P is constant, V changes.
Rubbish. In a gas in a piston the particles are free to move about the entire system, their kinetic energy is much much larger than their potential energy. In a solid the potential energy is huge compared to the kinetic energy, so the particles stick together and they are free to move. Given a rubber band is actually a solid, saying that its more like a gas in a piston than a solid is lunacy.
Depends what you mean by keeping the spokes on the wheel. They are not intact spokes, they have been taken out, the middle third cut away, the free ends bent over to form hooks and the rubber band replaces the missing piece (i.e., they are supports for the rubber bands). It is impossible to get from the hub to the wheel via an intact spoke, all paths must go through a rubber band, and this means the bands have a huge influence on locating center of mass relative to center of hub.
@kurpochelo Well then it would go the other way, exactly as my first explanation for the wheel would suggest, but I suspect it would turn very slowly if at all because the expansion you could achieve in this way would barely shift the center of mass and the resulting torque would likely not overcome the hub friction. This would only work with a very highly balanced wheel, probably in a vacuum and with good heat control, and with an extremely low friction bearing (maglev perhaps?)
"And second, if there IS no contraction of the rubber band, then how do you explain the shift in the center of mass of the wheel that makes it rotate."
Who said there is not contraction. You are mixing cause and effect. The center of mass shift precisely because the tension in the bands changes on both sides, which in turn, stretches one band and squeezes the other.
We're talking about the same thing in different terms here, so I think we're both right. I still don't see how this connects to your original claim that I am wrong about the rotation direction.
Of course, that was the whole point! Have a read of doubleKlutch's comment @Coonstev down below. The goal in science is not to be correct 100% of the time, that's just plain arrogance. The idea is to come up with hypotheses and explanations and try to prove them right or wrong. I developed an initial hypothesis based on common sense knowledged and showed it needed to be modified to account for a peculiarity.
It was a hidden lesson for my students about the scientific method.
I'm sorry, but why did you offer the incorrect explanation at the onset (that RB's expand when heated)? Not a very professional way to go about things if you want to be taken seriously.
He's trying to engage his students. His language clearly states that this is what you 'would' expect, as most things expand when heated. His students, theoretically, nod along in passive submission, as usual. Then, wtf, it's not doing what he said! Now he's established a problem for the students to solve; it provokes their natural curiosity.
He could have simply said, "Rubber bands expand when heated," but that would have been instantly forgettable.
I wonder, if the wheel is much heavier, would the engine not run faster, producing more power? Also, would it not be better to cover the rest of the wheel, so the lamp shines only to the rubbers that should expand.
@cyberdustz I'm not sure heavier helps, but balance in the wheel is absolutely vital. I think you can get more out of it by managing the heatloads, if I was trying to engineer this more, I'd be focussing on trying to get as much of the heat as possible to turn up in length change in the rubber bands, but I think you'd also need to think about expansion and contraction rates. Trying to push the efficiency on this would be a fun project.
@micolich memory wire.I hope I spelled it right,..it bends and contracts alot.look up nitinol heat engine on youtube.it will be a red box and blue box side by side.
@micolich now im thinking you would have to emerse one end in cold water to contract it,but the friction....unless you packed dry ice so loosely around it it produced no friction.
the heat isn´t doing eny work on the wheel. all the energy it has is transfered trough the air and the rubber bands. the temperature of the rubber band is lower than the air since its ability to transfer heat is slower. the heat isn´t doing eny work on the rubber bands. if you have a heat transfer trough different elements at the same time, is that doing work? the energy in form of heat isn´t converted into motion, becuase gravity is turning the wheel when there is an imbalance.
You had it right the first time. The rubber bands lose tension and expand when heated, causing a greater portion of the outer hub to move to the left. The axle is like the fulcrum on a balance scale and since its now out of balance, it rotates in to the left, counter-clockwise.
The way rubber bands work is that there are filaments and particles. When the filaments are straightened, the particles shake and bump against them, causing a tendency to kink and curl up. So, if you increase the heat, the particles shake faster, and the filaments get more tension on them.
This guy is explaining it totally wrong. Rubber CONTRACTS when it is heated. This causes the thowing of the centre of gravity! The whole point of this experiment is to show how counter-intuitive it is.
If you spun the wheel would it continue to spin as long as the floodlights were on or would the added friction of the air require too much momentum compensation for it to spin at such a high speed? I imagine there is a certain maximum velocity that the floodlights could possibly generate thus gradually slowing the wheel until it reaches that point, correct? Or perhaps the increased speed would render the floodlights ineffectual, not allowing enough time for significant contraction?
Thanks, Interesting. So this could be solar powered if say 75% of wheel where covered/insulated. The remaining uncovered area of wheel subject to focused Sunlight.
Has anyone ever tried this with a larger scale wheel, using things like those large black rubber bands that I've seen used to keep ceramic molds held together, outdoors with the majority of the wheel shielded and insulated from the direct sunlight, with a slight arc exposed? Maybe with a slight magnification from a low power fresnel lens? I'm sure that one couldn't expect a tremendous amount of work to be performed, but it would be an interesting experiment?
Yeah, laqtor is right, its just a standard bike wheel with the spokes cut. You cut the middle 1/3 of the spokes out, and bend them over to make hooks for the rubber bands to loop over. For better performance try to use a wheel that is well balanced and with a good low-friction bearing in the hub. We use blue-tack to balance out the wheel.
I'm just about to film a follow-up video on this one, so stay tuned...
Joule Effect: If a freely suspended rubber strip is loaded/stretched and subsequently heated, the strip will contract and lift the load. Conversely, an unloaded strip when heated expands to the coefficient of expansion for that rubber.
This phenomenon of contraction is termed the Joule effect and occurs only when heating a stretched rubber object.
Nah, that's a different problem that I was trying to solve. Can't remember what it was, looks like some kind of quadratic (perhaps I was using the lion attack on a cubic from memory?)
Great question. If it did I suspect it would be small, but a convection cell could drive the wheel. A more refined experiment would be to do the whole experiment in a vacuum to eliminate that possibility, it would take a bit of effort though.
That was kind of intentional, science isn't about being right the first time every time, its about coming up with a sensible hypothesis, testing it, and then using the results to make a better one. That's the moral of the story here, the sensible first guess is wrong, and you learn that rubber contracts rather than expands when heated - that's science...
even i, a 15 year old knows that red light is the closest is the closest in the electromagnetic spetrum from visable light to infra-red, through which heat is transmitted
Richard P. Feynman, the great physician, has a really nice explanation for this behaviour (not entirely accurate, but very understandable, even without a scientific background), just search for "feynman rubber bands" on youtube :)
The underlying assumption to your theory is that the centre is not fixed... However, the centre of the wheel is fixed and if the rubber bands on the right were expanded, the perimeter would bulge out slightly on the right - shifting the centre of mass to the right a little bit.
Here's how I would've predicted the rotation initially, and counterclockwise to boot:
"As the rubber bands are heated on the viewer's right side of the wheel they expand, thus relaxing some of the tension they are exerting. Consequently, the center of mass is pulled slightly to the viewer's left, where the cooler bands are exerting greater tension. Thus, as greater mass has accumulated to the left, the wheel 'falls' left, or in other words spins to the left, in a counterclockwise rotation."
That would of course have been the wrong explanation, but at least you wouldn't have had to revise it at the end to accouont for rubber bands contracting when heated...lol
Don't let this put you off by any means, but this can be a tricky demo to get working well, persistence is the key. The engine generates a miniscule torque, so any imbalance that the engine needs to fight against will stop it. When it gets working, you can start deliberately imbalancing by adding mass on the rim, and you'll see how little it takes.
how do you build the frame work and how can i hold it up the one i made isnt working and ive checked everyting could it ve that the lamp isnt as powerfull enough
The framework is just a laboratory retort stand, possibly locked to a bench with a g-clamp. To hold it, we extended the axle by adding a metal rod with a mating thread for the axle ends (which normally have nuts that lock them on the bicycle frame).
Re: trouble shooting, its often not the power in the lamps, its how free and balanced the wheel is. You need a good bearing and you need to not have a 'low-point' in the wheel. By this I mean...
... that if you set the wheel at random, it doesn't spontaneously rotate to have a particular point sitting at the bottom. If you have a 'low point', then the engine has a torque that it has to fight against, and it won't win. The wheel needs to be well balanced, good bearing, no low point, and then it doesn't take much heat at all to get it to spin reasonably fast.
what law of thermodynamics does this demonstrate and how exactly and can you give me a little more detailed instructions to make it please id appreciate the help
Making it is easy. Get old bike wheel, remove tire and tube. Extend the axle with metal bar and mount on a stand. Take wire cutters and cut the middle third out of each spoke. Bend the cut spoke ends over to make little hooks. Replace the middle third of each spoke with a rubber band. Add blue-tack or putty to rim to re-balance the wheel. Get two 100W (or higher) IR lamps (floodlights with red plastic over them will probably do) and shine on the rubber bands, and hopefully the wheel spins.
While its not setting out to demonstrate either law specifically, it still obeys them both. The 1st law is just conservation of energy, electricity is supplied to lamp, makes heat, most of which is lost to the room, and some makes the wheel spin. And the 2nd law just says the entropy of an irreversible process must increase, and given we're dumping so much heat, this is most certainly a very irreversible process. The efficiency of this engine is very low. But if you turn the light off, it stops.
love the video man
MrJonkelp 4 weeks ago
cool video... if this invention will push through then, who knows...this might be the solution to many problems! =)
iLOVENATURE2011 2 months ago
@iLOVENATURE2011 Hahah, probably not. This is a pretty old design and the efficiency is awful. I think it only survives as a neat little demonstration of how simple the thermodynamic idea of an engine can be.
micolich 2 months ago
@iLOVENATURE2011 haha two heat lamps at probably 200W each putting about (SWAG) 2W into spinning wheel... 0.5% efficiency. Heat engines have something to provide, no doubt, but this experiment is more in the "gee whiz" category than the future of energy conversion category.
pbryn1983 1 month ago
1:02 You say that when rubber bands expand when they get hot, this is not true - they shrink. This is demonstrated by the center of mass shifting away from the heat source 1:57.
AtomicLibido 6 months ago
@AtomicLibido At 0:59 I say "what you would think is going to happen...", and the point is that I'm trying to demonstrate that the system runs in a counterintuitive manner.
Cripes, if I had $50 for every 'smart cookie' who watches half this video and thinks its cool to call me on a mistake that actually isn't a mistake (its a deliberate attempt to point out that things aren't always what you expect in science), I would have my own multimillion $ studio and competing with mythbusters... sheesh!
micolich 6 months ago 14
@AtomicLibido lol PWND
RajDrummer1 5 months ago
Comment removed
Rapchaid 10 months ago
If you used black rubber bands and some kind of reflecting material behind the light you could make this quite a bit more efficient, couldn't you?
sug15 10 months ago
@sug15 Yeah you could. It's hard to say how much of a boost it would give you, probably not insignificant, but I also wouldn't say that its so radical that you suddenly have something that's anything more than a curiosity.
micolich 10 months ago
Neat video! I am doing this project for thermo class now. Can you please inform me of any calculations that may be useful in explaining work, energy and heat loss? The energy which i think is elastic potential is most confusiing to me. Please help. Thanks
Tylesaurus 10 months ago
Hi, I am a student currently taking physics in high school and I used your video to make this engine to show in my class. I had no trouble cutting and bending the spokes and stringing the rubber bands but I'm having difficulty shifting the center of mass to the middle of the wheel, where it's supposed to be. I have tried rebending the spokes, but it isn't helping. How did you fix this problem?
ETG0818 11 months ago
@ETG0818 The easiest way is to weight up the wheel. So ours has a strip of metal that runs inside the tire groove. When we first made it, we removed metal from this to get the mass into the right place. But the balance shifts often as you replace the rubber bands, because they all have slightly different tensions, etc. So we now balance the wheel as they do on cars, by adding weight opposite to the side that falls under gravity. I use blue-tack for this (its much like plasticine).
micolich 11 months ago
@ETG0818 Just set the wheel in some position and watch it rotate to where it stops, the heaviest bit will then be at the bottom, so add mass to the top of the wheel. Repeat many times until whenever you set the wheel, irrespective of where it is in its rotation, it doesn't move any more. Then its balanced. Takes a lot of adding and removing mass, and can be a good 30-60 minutes worth of work to get it right. (But there's always a lot of set up time invested in a good science demo ;) )
micolich 11 months ago
my car is powered by that =)
theRYNchannel 11 months ago
it turns in the opposite direction. your explanation was wrong.
kurpochelo 1 year ago
@kurpochelo
Ahhh, ok, I'm going to make you be more precise if you're going to make accusations of wrong. I give two explanations in the video. In the first, the heated side rotates downward (i.e., clockwise) because the bands expand. This is the naive expectation. It really goes the other way (i.e. anticlockwise) because rubber bands contract when heated. I believe this is quite clear (my students got it, so did many other viewers).
So, your argument is?
micolich 1 year ago
rubber bands neither contract nor expand when heated. Their tension increases when they get heated.
kurpochelo 1 year ago
@kurpochelo
OK, two questions then. How does the tension increase without a material contracting unless the material is held at a fixed length by some mechanism (and its not in this case)? And second, if there IS no contraction of the rubber band, then how do you explain the shift in the center of mass of the wheel that makes it rotate.
Your answer here doesn't agree with textbook knowledge of mechanics.
micolich 1 year ago
@micolich
"How does the tension increase without a material contracting unless the material is held at a fixed length by some mechanism (and its not in this case)?"
If you heat a gas confined in a vessel of constant volume does its pressure not increase?
kurpochelo 1 year ago
@kurpochelo
Yes, if I heat a gas at constant volume, the pressure rises. But there are two problems now. First, a rubber band is not a gas, its a solid, and in solids potential energy is everything, in a gas its mostly kinetic. Second, if you translate the analogy across, my rubber band is not at fixed volume. Like I said, there is nothing stopping the rubber band changing its length. The correct analogy would be a gas in a rubber balloon, and then if I heat it, P is constant, V changes.
micolich 1 year ago
@micolich Actually, a rubber band is more like a gas confined in a piston than it ts like a solid object.
kurpochelo 1 year ago
@kurpochelo
Rubbish. In a gas in a piston the particles are free to move about the entire system, their kinetic energy is much much larger than their potential energy. In a solid the potential energy is huge compared to the kinetic energy, so the particles stick together and they are free to move. Given a rubber band is actually a solid, saying that its more like a gas in a piston than a solid is lunacy.
micolich 1 year ago
@micolich well, if it is rubbish, how would the wheel turn if you kept the metal spokes on the wheel?
kurpochelo 1 year ago
@kurpochelo
Depends what you mean by keeping the spokes on the wheel. They are not intact spokes, they have been taken out, the middle third cut away, the free ends bent over to form hooks and the rubber band replaces the missing piece (i.e., they are supports for the rubber bands). It is impossible to get from the hub to the wheel via an intact spoke, all paths must go through a rubber band, and this means the bands have a huge influence on locating center of mass relative to center of hub.
micolich 1 year ago
@micolich Just take a new balanced wheel, paint the spokes black and see how the wheel would turn.
kurpochelo 1 year ago
@kurpochelo Well then it would go the other way, exactly as my first explanation for the wheel would suggest, but I suspect it would turn very slowly if at all because the expansion you could achieve in this way would barely shift the center of mass and the resulting torque would likely not overcome the hub friction. This would only work with a very highly balanced wheel, probably in a vacuum and with good heat control, and with an extremely low friction bearing (maglev perhaps?)
micolich 1 year ago
@micolich
"And second, if there IS no contraction of the rubber band, then how do you explain the shift in the center of mass of the wheel that makes it rotate."
Who said there is not contraction. You are mixing cause and effect. The center of mass shift precisely because the tension in the bands changes on both sides, which in turn, stretches one band and squeezes the other.
kurpochelo 1 year ago
@kurpochelo
We're talking about the same thing in different terms here, so I think we're both right. I still don't see how this connects to your original claim that I am wrong about the rotation direction.
micolich 1 year ago
@micolich You gave two explanations with different predictions for the direction of rotation. It follows that at least one is incorrect.
kurpochelo 1 year ago
@kurpochelo
Of course, that was the whole point! Have a read of doubleKlutch's comment @Coonstev down below. The goal in science is not to be correct 100% of the time, that's just plain arrogance. The idea is to come up with hypotheses and explanations and try to prove them right or wrong. I developed an initial hypothesis based on common sense knowledged and showed it needed to be modified to account for a peculiarity.
It was a hidden lesson for my students about the scientific method.
micolich 1 year ago
Very cool but when the lamps heat up the the rubber bands it makes them want to contract more not expand. Rubber bands work off of heat.
stramarama 1 year ago
I converted both my bike wheels to this rubber band style wheel.
Now when I ride at night the wheels produce red light so motorists will see me.
Thanks for the great tip
vmoko 1 year ago
I'm sorry, but why did you offer the incorrect explanation at the onset (that RB's expand when heated)? Not a very professional way to go about things if you want to be taken seriously.
Coonstev 1 year ago
@Coonstev
He's trying to engage his students. His language clearly states that this is what you 'would' expect, as most things expand when heated. His students, theoretically, nod along in passive submission, as usual. Then, wtf, it's not doing what he said! Now he's established a problem for the students to solve; it provokes their natural curiosity.
He could have simply said, "Rubber bands expand when heated," but that would have been instantly forgettable.
doubleKlutch 1 year ago
its turning the wrong way!!!!!!!!
TheKrazykool809 1 year ago
cover the heated end,and squirt coolent on the exposed nitinol wire ,recycled by a pump .
alicenchains59 1 year ago
I wonder, if the wheel is much heavier, would the engine not run faster, producing more power? Also, would it not be better to cover the rest of the wheel, so the lamp shines only to the rubbers that should expand.
cyberdustz 1 year ago
@cyberdustz I'm not sure heavier helps, but balance in the wheel is absolutely vital. I think you can get more out of it by managing the heatloads, if I was trying to engineer this more, I'd be focussing on trying to get as much of the heat as possible to turn up in length change in the rubber bands, but I think you'd also need to think about expansion and contraction rates. Trying to push the efficiency on this would be a fun project.
micolich 1 year ago
What if you used nitinol wire? wouldnt that greatly increase the output of power?
alicenchains59 1 year ago
@alicenchains59 Nitinol wire? Tell us more...
micolich 1 year ago
@micolich memory wire.I hope I spelled it right,..it bends and contracts alot.look up nitinol heat engine on youtube.it will be a red box and blue box side by side.
alicenchains59 1 year ago
@micolich now im thinking you would have to emerse one end in cold water to contract it,but the friction....unless you packed dry ice so loosely around it it produced no friction.
alicenchains59 1 year ago
the heat isn´t doing eny work on the wheel. all the energy it has is transfered trough the air and the rubber bands. the temperature of the rubber band is lower than the air since its ability to transfer heat is slower. the heat isn´t doing eny work on the rubber bands. if you have a heat transfer trough different elements at the same time, is that doing work? the energy in form of heat isn´t converted into motion, becuase gravity is turning the wheel when there is an imbalance.
coldarc 1 year ago
Convection...
Try this in a vaccum chamber and see how much less work it produces.
cdavie5 1 year ago
@cdavie5 a dumb question, would it be more efficient under pressure?I would think it would be more output with no atmosphere.
alicenchains59 1 year ago
Comment removed
shadowmonstr 9 months ago
This has been flagged as spam show
@cdavie5
"Convection...
Try this in a vaccum chamber and see how much less work it produces."
I pondered the same...
shadowmonstr 9 months ago
SCIENCE !!!!!
Berelore 1 year ago
Ha,, ha. You'd get more power from blowing on it.
Nomoreidsleft 1 year ago
How many horsepower? :)
DoubleM55 1 year ago
@DoubleM55 Nomoreidsleft is kind of right, the power in this machine is miniscule, but that's not really the point.
micolich 1 year ago
You had it right the first time. The rubber bands lose tension and expand when heated, causing a greater portion of the outer hub to move to the left. The axle is like the fulcrum on a balance scale and since its now out of balance, it rotates in to the left, counter-clockwise.
Peopleunit 1 year ago
@Peopleunit Ahhh, no, rubber bands contract when heated.
micolich 1 year ago
@micolich Yes Rubber bands do contracts more when heated. The more energy gives more strength to the contraction.
LinuxNavigator 1 year ago
@Peopleunit
The way rubber bands work is that there are filaments and particles. When the filaments are straightened, the particles shake and bump against them, causing a tendency to kink and curl up. So, if you increase the heat, the particles shake faster, and the filaments get more tension on them.
Fordi 1 year ago
@Peopleunit But if they expanded, the wheel would be going clockwise, not couter-clockwise
MrKaddan 1 year ago
Comment removed
Peopleunit 1 year ago
Hehe das Badetuch aufn Sitz hatte ich auch ma ^.^ "1qm Freistaat Bayern"
English: Hehe i had this badtowel too it says "1qm (quadratmeter) Freistaat Bayern"
"1 square meter free State of Bavaria"
videofreakcologne 1 year ago
now put on your bike
qazwas4321 1 year ago
rubber doesn't expand under heat though. it contracts. It expands under cold temperatures, but the concept still works!
benrweston 1 year ago
@benrweston that actually makes more sense. I was wondering why the wheel is spinning the opposite way..
grendelee 1 year ago
@grendelee what's funny is that the motion he describes would be accurate for contraction, but he says expansion.
benrweston 1 year ago
@benrweston he explains that later in the video. I just didnt see that far
grendelee 1 year ago
This guy is explaining it totally wrong. Rubber CONTRACTS when it is heated. This causes the thowing of the centre of gravity! The whole point of this experiment is to show how counter-intuitive it is.
HelmutVillam 1 year ago
@HelmutVillam watch the whole video silly
swt683 4 months ago
If you spun the wheel would it continue to spin as long as the floodlights were on or would the added friction of the air require too much momentum compensation for it to spin at such a high speed? I imagine there is a certain maximum velocity that the floodlights could possibly generate thus gradually slowing the wheel until it reaches that point, correct? Or perhaps the increased speed would render the floodlights ineffectual, not allowing enough time for significant contraction?
XTrumpet63X 1 year ago
What are You thinking about ? Metal spring config with a larger mass and a solar colector? Hmmmmm My wheels are turning.....
GIZMOPRIME 2 years ago
Thanks, Interesting. So this could be solar powered if say 75% of wheel where covered/insulated. The remaining uncovered area of wheel subject to focused Sunlight.
1996DNA 2 years ago
Yes, you could use a solar concentrator to generate the heat to run this engine.
micolich 2 years ago
@micolich you would have to filter UV light out because rubber degrades under intense UV light
deelkar 1 year ago
so what is the point of this? that is a terribly Inefficient way to turn a wheel? I just don't see the point?
TheFunkyStrings 2 years ago
@TheFunkyStrings It's a physics experiment, idiot.
UncleKennybobs 2 years ago
Has anyone ever tried this with a larger scale wheel, using things like those large black rubber bands that I've seen used to keep ceramic molds held together, outdoors with the majority of the wheel shielded and insulated from the direct sunlight, with a slight arc exposed? Maybe with a slight magnification from a low power fresnel lens? I'm sure that one couldn't expect a tremendous amount of work to be performed, but it would be an interesting experiment?
brianwesley28 2 years ago
what type of wheel is this?
dorkella411 2 years ago
a bicycle
laqtor 2 years ago 2
Yeah, laqtor is right, its just a standard bike wheel with the spokes cut. You cut the middle 1/3 of the spokes out, and bend them over to make hooks for the rubber bands to loop over. For better performance try to use a wheel that is well balanced and with a good low-friction bearing in the hub. We use blue-tack to balance out the wheel.
I'm just about to film a follow-up video on this one, so stay tuned...
micolich 2 years ago
This has been flagged as spam show
Nice Job.... good demonstration!
Joule Effect: If a freely suspended rubber strip is loaded/stretched and subsequently heated, the strip will contract and lift the load. Conversely, an unloaded strip when heated expands to the coefficient of expansion for that rubber.
This phenomenon of contraction is termed the Joule effect and occurs only when heating a stretched rubber object.
kdober6 2 years ago
Need all of that math from that board to accomplish this?
deaftodd 2 years ago
Nah, that's a different problem that I was trying to solve. Can't remember what it was, looks like some kind of quadratic (perhaps I was using the lion attack on a cubic from memory?)
micolich 2 years ago
its the hot air making a draft
corneliusmattey 2 years ago
Great question. If it did I suspect it would be small, but a convection cell could drive the wheel. A more refined experiment would be to do the whole experiment in a vacuum to eliminate that possibility, it would take a bit of effort though.
micolich 2 years ago
How about applying cold on the opposite side.
KevinMicKnapp 2 years ago 3
Oooooh, I see a sequel for this video coming....
micolich 2 years ago
Superb, i watched this after watching feynman explain rubber bands! :D
itsabomberscope 2 years ago 3
Me too, ha ha ha ha ha.
FreindlyRanger 2 years ago
wow, absolute fail on explaining which way it will spin. good god, i laughed when he said it would spin CW then laughed a bit more when it didn't.
wheatkings14 2 years ago
he was making a point.... sigh
jimmybilbo 2 years ago
oh yeah, i know he was trying to explain how it worked and all he just pretty well said the opposite of what actually occurred.
wheatkings14 2 years ago
you don't have many friends do you :)
sausage4mash 2 years ago
No :.... (
wheatkings14 2 years ago
what made you make a harsh comment like that, there was no good reason to say that.
mooobtube 2 years ago
talking to me mooob ?
sausage4mash 2 years ago
yes
mooobtube 2 years ago
This has been flagged as spam show
Fail..
Should have tried this before you made the vid..
Still a fairly interesting concept, though..
JesterAzazel 2 years ago
Ahhh, I'm confused. It worked, so why is that a failure?
micolich 2 years ago
ok, not a failure, but you were wrong about which way it spun.. spun? spinned?
But mostly I was just bustin' your chops.. :P
JesterAzazel 2 years ago
That was kind of intentional, science isn't about being right the first time every time, its about coming up with a sensible hypothesis, testing it, and then using the results to make a better one. That's the moral of the story here, the sensible first guess is wrong, and you learn that rubber contracts rather than expands when heated - that's science...
micolich 2 years ago
interesting
Benefitben1 2 years ago
Our eyes react most to the green color. ;)
warvector 2 years ago
I don't understand why you chose to use red filters. Red is the lowest energy of visible light. Wouldn't the optimal choice have been blue/violet?
totlyepic 2 years ago
The red filter will absorb the higher wavelengths (and re-emit that light as heat), and only let the red (low-energy) light pass through.
Niffux 2 years ago 11
actually, low wavelengths = high energy
hsze 1 year ago
even i, a 15 year old knows that red light is the closest is the closest in the electromagnetic spetrum from visable light to infra-red, through which heat is transmitted
SkinnyJeansLovee 2 years ago
Richard P. Feynman, the great physician, has a really nice explanation for this behaviour (not entirely accurate, but very understandable, even without a scientific background), just search for "feynman rubber bands" on youtube :)
linuxx0r 2 years ago
Physicist, not physician.
ilmmad 2 years ago 8
yep, you're right :P
english is not my mother tongue
linuxx0r 2 years ago
beginswithz:
The underlying assumption to your theory is that the centre is not fixed... However, the centre of the wheel is fixed and if the rubber bands on the right were expanded, the perimeter would bulge out slightly on the right - shifting the centre of mass to the right a little bit.
adinclik 2 years ago
Here's how I would've predicted the rotation initially, and counterclockwise to boot:
"As the rubber bands are heated on the viewer's right side of the wheel they expand, thus relaxing some of the tension they are exerting. Consequently, the center of mass is pulled slightly to the viewer's left, where the cooler bands are exerting greater tension. Thus, as greater mass has accumulated to the left, the wheel 'falls' left, or in other words spins to the left, in a counterclockwise rotation."
beginswithz 2 years ago
That would of course have been the wrong explanation, but at least you wouldn't have had to revise it at the end to accouont for rubber bands contracting when heated...lol
beginswithz 2 years ago
Just keep the spokes and use a flame thrower. Anything pyrotechnic should help the little shits develop an interest in applied physics!
Subutubiata 2 years ago
Don't let this put you off by any means, but this can be a tricky demo to get working well, persistence is the key. The engine generates a miniscule torque, so any imbalance that the engine needs to fight against will stop it. When it gets working, you can start deliberately imbalancing by adding mass on the rim, and you'll see how little it takes.
micolich 2 years ago
how do you build the frame work and how can i hold it up the one i made isnt working and ive checked everyting could it ve that the lamp isnt as powerfull enough
cardcutter 2 years ago
The framework is just a laboratory retort stand, possibly locked to a bench with a g-clamp. To hold it, we extended the axle by adding a metal rod with a mating thread for the axle ends (which normally have nuts that lock them on the bicycle frame).
Re: trouble shooting, its often not the power in the lamps, its how free and balanced the wheel is. You need a good bearing and you need to not have a 'low-point' in the wheel. By this I mean...
micolich 2 years ago
... that if you set the wheel at random, it doesn't spontaneously rotate to have a particular point sitting at the bottom. If you have a 'low point', then the engine has a torque that it has to fight against, and it won't win. The wheel needs to be well balanced, good bearing, no low point, and then it doesn't take much heat at all to get it to spin reasonably fast.
micolich 2 years ago
what law of thermodynamics does this demonstrate and how exactly and can you give me a little more detailed instructions to make it please id appreciate the help
cardcutter 2 years ago
Making it is easy. Get old bike wheel, remove tire and tube. Extend the axle with metal bar and mount on a stand. Take wire cutters and cut the middle third out of each spoke. Bend the cut spoke ends over to make little hooks. Replace the middle third of each spoke with a rubber band. Add blue-tack or putty to rim to re-balance the wheel. Get two 100W (or higher) IR lamps (floodlights with red plastic over them will probably do) and shine on the rubber bands, and hopefully the wheel spins.
micolich 2 years ago
While its not setting out to demonstrate either law specifically, it still obeys them both. The 1st law is just conservation of energy, electricity is supplied to lamp, makes heat, most of which is lost to the room, and some makes the wheel spin. And the 2nd law just says the entropy of an irreversible process must increase, and given we're dumping so much heat, this is most certainly a very irreversible process. The efficiency of this engine is very low. But if you turn the light off, it stops.
micolich 2 years ago
imagine the torque of that thing!
fearnstarr 3 years ago
Hahaha, yeah. It can barely lift a flea. :)
micolich 2 years ago