The flying pig may hit the fan of Mender's stationary wind turbine.
Fan law #3 .Power is proportional to V^3.
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Split Thread The validity of classical physics (split from: DWFTTW)
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The flying pig may hit the fan of Mender's stationary wind turbine.
Fan law #3 .Power is proportional to V^3.
No. "The force" is that available to do work, not the drag. Of course the balloon is coupled to the wind by drag ( though figuratively, because it is really momentum exchange), but not without a velocity differential,between it and the wind. The turbine fan is different, because it is stationary in Groundian terns, and sees a force that always increases with velocity. That means power is proportional to V^3.
That cannot apply to balloons or parachutes, because they would then be able to produce more power than the wind.
recursive prophet
Graduate Poster
Fan law #3 .Power is proportional to V^3. C'mon guys, you're on a roll, keep up the pace! The pigs are using the negative drag of their rumps to ride the real wind and the droppings that are about to hit member's stationary turbine. 
Really funny reply sol. Dan_O-the trend is your friend!
Really funny reply sol. Dan_O-the trend is your friend!John Freestone
Graduate Poster
A BRIEF INTERMISSION...
Speaking of simplifying things, I was just thinking how unecessarily complicated it was to say that in orbit the gravitational force is balanced by the centrifugal force, to explain the weightlessness felt. I said that that was problematic because there is not usually thought to be such a beast as centrifugal force.
There is the simpler description, which is that there is only the gravitational force, which is the centripetal force required to cause the acceleration, changing the velocity by changing the vector. When you take a turn in a car, similarly, in the horizontal direction, there is just the centripetal force applied via the seatbelt, door, etc. making your body follow that curve, and via the road on the wheels to turn the car.
Forces come in pairs though, so doesn't this description break Newton's Third? Oh no, of course, there is a gravitational force on the planet, equal to the force on the orbiting body. So, is there a centrifugal force, too, of a person against their seatbelt? Isn't that what you feel at the end of the string when you whirl something round? The mass may 'experience' an inward force, but you definitely feel an outward pull.
Is that better, according to Newton? There are always pairs of forces, but the body to which they apply are different, so each can feel a net unbalanced force. In the usual situation where your weight is resisted by the normal force, it's easy to think of those as the pair of forces that Newton's Third refers to, but are there actually four forces - your weight, the "weight" of the earth (it's gravitational response up towards you), the normal force, i.e. the physical resistance of the earth's surface, and your physical resistance to that, its pair?
...OK. Ding ding, round 83
Speaking of simplifying things, I was just thinking how unecessarily complicated it was to say that in orbit the gravitational force is balanced by the centrifugal force, to explain the weightlessness felt. I said that that was problematic because there is not usually thought to be such a beast as centrifugal force.
There is the simpler description, which is that there is only the gravitational force, which is the centripetal force required to cause the acceleration, changing the velocity by changing the vector. When you take a turn in a car, similarly, in the horizontal direction, there is just the centripetal force applied via the seatbelt, door, etc. making your body follow that curve, and via the road on the wheels to turn the car.
Forces come in pairs though, so doesn't this description break Newton's Third? Oh no, of course, there is a gravitational force on the planet, equal to the force on the orbiting body. So, is there a centrifugal force, too, of a person against their seatbelt? Isn't that what you feel at the end of the string when you whirl something round? The mass may 'experience' an inward force, but you definitely feel an outward pull.
Is that better, according to Newton? There are always pairs of forces, but the body to which they apply are different, so each can feel a net unbalanced force. In the usual situation where your weight is resisted by the normal force, it's easy to think of those as the pair of forces that Newton's Third refers to, but are there actually four forces - your weight, the "weight" of the earth (it's gravitational response up towards you), the normal force, i.e. the physical resistance of the earth's surface, and your physical resistance to that, its pair?
...OK. Ding ding, round 83
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Fan law #3 .Power is proportional to V^3. C'mon guys, you're on a roll, keep up the pace! The pigs are using the negative drag of their rumps to ride the real wind and the droppings that are about to hit member's stationary turbine.
http://www.cee1.org/ind/mot-rep/mot-rep-fanlaws.pdf
http://hypography.com/forums/physics-and-mathematics/8142-negative-thixotropy-vs-rheopexy.html
ETA:
Make a saturated suspension of cornstarch ( corn flour). Stir it, and see what happens.
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John Freestone
Graduate Poster
I said, didn't I? Invasion of the Non-Newtonian Fluids. Coming to a cinema near you. They said it couldn't be done, but he walked on custard anyway...
So negative drag can only be Newtonian to qualify? No, it can be either.
Still wondering about relevance, you know that Betz efficiency limit for a wind turbine is around 59%, power available in wind energy to power deliverable at the shaft, perhaps he didn't know as much as you. And you also realize that aircraft propeller efficiency is routinely 85% or more or the power in the engine shaft to the power transfered by the airframe.
But you might not have realized that the overall thermal efficiency of a Concorde in cruise is around 42%, yeah at Mach 2ish, better than many terrestrial power stations. But anyway, how does all this tally with you MPT theory, and how is it relevant to the cart on the treadmill?
Well written and informative Humber, keep it up!
I still believe you are making one error. In an earlier post, you seem to have substituted "Uniform" for "Constant" They are not the same.
I don't argue that a body in a gravity field has a constant acceleration, due to Gradient as you have pointed out. It DOES have UNIFORM acceleration, meaning every atom in it and close to it have an equal instantanious acceleration at any particular time. In this case, I don't see how an accelerometer could detect anything, as there will be no strain due to acceleration on the inertial member. The only thing it could theoretically detect would be the gravity gradient over it's own lenght. I own four piezo-electric gyros, as I use tham on my model helicopters. They are 1.5cm cubed. I doubt they are THAT sensitive.
Like I said, your last answer was very informative (though, if you never believed that an accelerometer could detect the actual acceleration due to gravity, you caould have said so implicitley), so if I'm still on the worng track, I'm all ears.
You might want to rethink a few of these points. And speaking of pouring water... ;
http://uk.youtube.com/watch?v=Xp2Uc9XvmjY
Mind the gravity Bob!
Regurgitating what others have been saying for a long time is not the same as learning, but it might be a start. Humber has a way of snatching defeat from the jaws of victory.
I wouldn't strike #8 off until he states that he has changed his mind and is able to demonstrate that. My bet is that he'll claim he was right all along and he was misunderstood.
Oh, look at that, he didn't understand after all. No pigs flying today. My bet is still on though.
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May depend upon the topic, perhaps.
I did remark that the overall efficiency of energy use in the USA is 13%.
(American Scientist Jan/Feb 2009)
The efficiency of those items is governed by the laws of conservation of energy/thermodynamics. Heat engines of the Concorde, by the Carnot Cycle.
MPT is about load matching in this case. When the load matches the power source, 50% of the available energy does work in the load, the remainder is lost in the source. That is not a necessary condition for maximum velocity, but the limiting case for available power.
Maximum velocity is governed by the available power. If the available power falls with velocity, as it does with an airborne object, but the load increases with velocity, as it does for an object dragged through air over the ground, you can see that a balance will be reached before windspeed.
More than free fall does.
It means that the cart on the treadmill cannot be taking energy from the "wind", and cannot reach windspeed, let alone stay there when there is no power consumption.
(That involves viewing the system, and not just from MPT.)
It is in no way a regurgitation. I mentioned power early on in the other thread, Mender. It was not I who confused stationary turbines with balloons!
If you now accept my argument (which you say is yours), you must accept that the zero force at windspeed claim, is false.
ETA;
Number *8 is the simplifying assumption of the meteorological balloon, and was used for the skater. From (V -Vb)^2. It is the same assumption you make; chutes can travel close to the wind.
I was using that to say that even in that case, you still have a problem, because even if load and chute have those same characteristics, the driving force from the chute falls with velocity, while the load increases with velocity. The limit will be reached before windspeed.
I also pointed that out, and to Rayleigh's and Drela's equations. Yes, they are different.
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For the case of the cart your claim of zero force at windspeed is false, Humber. You were not right all along and you're still not right. That means that you're still wrong. Not right = wrong. Got that?
The cart uses the energy that it harnesses from the speed difference between the air and the ground to overcome rolling resistance. If the speed difference between the air and the ground is high enough, the energy harnessed is sufficient to propel the cart at or above windspeed. Because of the "overdrive" gearing of the propeller, it can continue slow the air wrt the ground and continue to extract energy even though it is moving faster than the speed of the air over the ground (or the speed of the ground under the air).
My claim is that the cart continues to harness energy from the air/ground speed difference even when it is traveling faster than that speed over the ground.
Do you want to understand that?
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Hi John
As far as I'm concerned, centrifugal force is simply one of the "fictitious forces".
We only "see" that as a force from certain non-inertial frames of reference. Then there is the personal experience of "feeling" it which I guess you could describe as a visceral demonstration of a "self-based frame of reference". (Also non-inertial.)
There are definitely some very ambiguous and potentially confusing terms "floating around" this whole area. Taken being "weightless" for example. In terms of pure physics, we aren't actually without weight when we say we are experiencing "weightlessness" (because we're in free-fall, etc.). Our "apparent weight" is zero, simply because we are experiencing the state where there are essentially no internal stresses on body organs, etc. In other words our brains think we are without weight because the usual stresses are suddenly removed. But our "real weight" is still given by mass times "acceleration due to gravity". In other words, our "real weight" is the force exerted on our body by gravity, and that force doesn't disappear when we start to free-fall, or start orbiting the Earth.
On the other hand, centripetal force is a "real force" required to explain the curving path of some mass in an inertial frame of reference. It could be gravity acting on us as we orbit the earth, or it could be a car seat and safety belt, etc. acting on our body as we drive around a corner. But in the first case gravity is acting on each and every part part of our body that has mass so that we don't feel any internal stresses and strains, and we casually call that state being "weightless". In the second case, the force of the car seat, etc., acts directly on the exterior parts of our body and only indirectly (and slightly "later") on other internal organs through tension in ligaments and other tissues. We "feel" that happening. In other words, the two cases feel different, but it's only because gravity acts on the orbiting astronaut's body "all at once", while in the cornering car the centripetal force is applied to our internal organs via other means. Otherwise they'd continue in a straight line and things would get messy!
So, centrifugal force has nothing really to do with it as far as I'm concerned. That is just a pseudo force that the person in the car might claim to feel because of the sensations involved, or similarly a physicist might measure if using a frame of reference that was moving with the car. If we used a simplified model of a body consisting of just a bone and a brain connected with a piece of elastic ligament including nerves, then we might see the bone as being directly "forced" (by the seat belt, say) to follow the car's curving path. The brain initially tries to continue in a straight line (Newton's 1st law), but that means the elastic connecting ligament starts to stretch. That starts applying a force to the brain which then starts to follow around the curve also, and the brain also feels the ligament stretching via the nerves. Of course there are the reactions to those forces also, the brain pulls on the end of the ligament material, the bone pulls on the belt, and so on but that isn't exactly what I would call the "centrifugal force". If however, you are using a non-inertial frame so you do detect the centrifugal force, you would look upon the pairs on forces in a reversed sense. The brain pulls on the end of the ligament (for some reason that you're not entirely sure of!), the ligament stretches and eventually the tension in the ligament balances the mystery force acting on the brain so that it stops accelerating towards the side of the car. We hope so anyway!
Hmmm. That is all very long winded, and I'm sure you already know all of what I've said, but perhaps there might still be one or two useful "insights" in terms of interpretation buried in there somewhere. That's how I see it anyway!
Not my claim, but one generally held in this thread. I have said that zero force is impossible, that canoes have bow waves, etc. They are all related to power. The treadmill relies on there being zero or near-zero power at windspeed. The skater driven by a chute on the treadmill will eventually reach that near-zero power state, but a skater in wind, will not. That is because the treadmill is not "equivalent".
Rolling resistance is one component, and the drag of the vehicle as it travels through the air another.There is opposing drag downwind, too.
You cannot arbitrarily determine how much energy will be transferred to the cart from the wind.
It would first have to get to windspeed, even if plausible. The treadmill says nothing about that.
You cannot show that happens on the treadmill. All the power comes from the motor, and is minimal.
The only source is the difference between the cart and the wind. The wheels are part of the cart, that is all.
'Ground energy' cannot be shown to exist on the treadmill, for any gear ratio,
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