Downwind faster than the wind. Poll

[Ubergeekian]

But to respond. If the road were to pass energy onto the cart, then the road would be in a different state after the cart had gone. Is it? No it isnt. The road is stationary. Its at the same potential energy as it always was. Its at the same temperature.

It's moving at a different speed. No, really, of course it is. A force has been exerted on it and the force does work. Of course the mass of the earth is so large that the velocity change is imperceptible, but it's still there. As it is in much simpler case - the wind blowing against a tree changes the earth's velocity too. When you accelerate in your car you give the earth just as much momentum backwards as you give your car forwards.

 

[Porthandbuoy]

Effinell. Go offline for a few days, come back, and this thread's still running top of the list. Moronic.

How do I put an entire thread on ignore?

 

[Pierrome]

Effinell. Go offline for a few days, come back, and this thread's still running top of the list. Moronic.

How do I put an entire thread on ignore?

No, in fact it's the son of the original thread.
The original thread started by myself has died.
But it's offspring lives on.

 

[Ubergeekian]

I did my degree in Physics. I'd be the first to admit that was a long time ago and my brain isnt what it was when I was a young man. But with those caveats I can see no way that the vehicle could go dead down wind faster than the speed of the wind without breaking the laws of physics. Problem is trying to explain this in words rather than equations.

I'm happy with equations. Go on, give us some equations. Tell us which laws of physics, precisely, you think are being broken, and how.

 

[Ubergeekian]

There is no way the cart can go faster than the wind without using energy from the road, because the wind has stopped blowing in the right direction relative to the cart.

It all depends on your frame of reference. If fixed to the road, the energy comes from the wind - and there's no difficulty about that, since a fan blowing back into the tailwind will slow some of it down: after the cart has passed there will be less kinetic energy in the air.

 

[Porthandbuoy]

No, in fact it's the son of the original thread.
The original thread started by myself has died.
But it's offspring lives on.

Behold! If Heineken made trolls etc. etc etc.

 

[halfway]

Pierrome: "This example shows that you can extract energy from the relative movement between a medium that is static with respect to the earth, if you yourself are moving with respect to the earth."

Now we are getting there. You can extract energy from a force occurring between two object moving. That energy can be put into a battery and becomes none relative, or into a kettle for some tea. (thermal energy)

You do not need any double referencing to another fixed reference. All you need is two things and a resultant force (probably slowing them)

----

Ubergeekian: "When you accelerate in your car you give the earth just as much momentum backwards as you give your car forwards."

Very true, and supports the above, but the energy you have put into the system is in the form of momentum. Which is a relative energy.

So the energy expended in acceleration can be put to use, with reference to the earth, to accelerate the car.

However, it is also true that with reference to the car, the earth can be accelerated backwards away from it. The energy gained is relative to the car.

Finally if you reference everything to Pluto, the earth and the car can both be accelerated and both be given energy relative to Pluto. The values must sum to be the same as the energy the engine expended.

----

So in the end the cart and wheel extracts energy from the relative movement of the cart and the ground. This could be used to boil a kettle or charge a battery. Now you could consider that the energy is extracted from both the cart and the earth. But you could only do that if your delta velocities were referenced to Pluto.

If your delta velocity was referenced to the ground, then the ground would lose no energy and the cart would lose it all.

----

To conclude: since we are talking about a cart speed relative to the ground, (No other velocity seems appropriate) you can ONLY remove energy from the cart.

 

[halfway]

RAI: not ... Lightly - means without regard to consequences.
rapidly - means over a short space of time.

Now you want to disagree over possible outcomes and speed. I rest my case. Guilty as charged.

 

[snowleopard]

A small point....

There is a fair amount of talk about whether the prop is doing the propelling or the wheels. Take a look at this diagram from a few pages back:

As you may recall it was shown in a video where we see the upper surface being moved to the right and the vehicle moving to the right at about 3 x the speed.

Question - which wheel(s) are driving and which are being driven? The answer is that both must be serving both functions. Obvious enough when you realise that it is not one surface or the other providing the energy to propel the vehicle but the relative movement of the two.

So when you replace the upper wheel and surface by prop and air, the prop and the wheels work together to extract energy from the relative motion of air and ground and both contribute to the propulsion that converts that energy into movement.

 

[Ubergeekian]

Now we are getting there. You can extract energy from a force occurring between two object moving. That energy can be put into a battery and becomes none relative, or into a kettle for some tea. (thermal energy)

You will recall, of course, that you cannot use any of the thermal energy unless you have another, lower, temperature available. And that batteries have potential differences, not potentials.

Ubergeekian: "When you accelerate in your car you give the earth just as much momentum backwards as you give your car forwards."

Very true, and supports the above, but the energy you have put into the system is in the form of momentum. Which is a relative energy.

1. Momentum is not energy.
2. All energy is relative

 

[fireball]

Halfway - we seem to have been arguing at cross purposes - I was referring to lower than wind speed vessels whilst you were talking about faster than wind vessels. Ho hum!!

 

[halfway]

snowleopard:

Just a few points. In the diagram it shows no change in velocity. So therefore there is no energy expended in the diagram.

If you had added friction forces then the gearing would have used the relative energy to overcome the friction and caused the unit to heat up.


However, you did label the speed of the cart and the speed of the ruler, I assume therefore they are referenced to the ground.

So if we were to increase the force on the ruler and accelerate the ruler to 2V and the cart to 6V the added energy is relative to the ground. Since the V's are specified relative to the ground.

So therefore the energy was supplied relative to the ground. Both the energy reference and the force reference must be the same. By specifying the 3V to be referenced to the ground you mandate the force calculation to be referenced to the ground.


Therefore the ruler supplied the energy by a force over a time period.


Since friction generated heat, is a non-relative energy, the energy is supplied by the relative force between the ruler and the ground. Both will push. However to calculate the energy you could use the force on the ruler w.r.t to ground. Or the force on the ground w.r.t the ruler.

PS. It is nearly time for penalty points. So take care.



Ubergeekian: I said "the form of momentum"

The value of the energy is different to the value of the bodies momentum. But it is due to its momentum that it has energy. If I impart momentum in a space ship to a brick it will still hurt. I can not impart a momentum without giving it energy. Both have to have the velocity referenced to some common point.

"All energy is relative": Yes but some references are just simply obvious. Temperature is relative to a kind of very fixed bottom point. Chemical energy is referenced to the atom that is part of the bond. It is hardly referenced to the dog next door.

Extraction of energy is a relative thing as you have to have something to fight against or somewhere to put the atom afterwards.

In the end there is actually no different types of energy either. Since energy is our word to explain the world. We have made it a convention to talk about the change of certain types of energy that are beyond our comprehension like gravitational potential energy. It is just a simple model so that day to day life can be calculated.

 

[halfway]

Ubergeekian: "You need some mechanism for extracting energy from the ground as it passes by (fast) and transferring it to the air as it moves by (not as fast)."

Please remember your statement that drove me to insanity. In the above statement you reference the speed to the ground. Yet you seem to get energy from your reference, the ground, and transfer it to the air.

I rest my case.

 

[Ubergeekian]

Ubergeekian: "You need some mechanism for extracting energy from the ground as it passes by (fast) and transferring it to the air as it moves by (not as fast)."

Please remember your statement that drove me to insanity. In the above statement you reference the speed to the ground. Yet you seem to get energy from your reference, the ground, and transfer it to the air.

My statement was clearly using a frame of reference fixed to the cart.

 

[halfway]

Ubergeekian: "My statement was clearly using a frame of reference fixed to the cart. "

But that does not work either. As the intention of the cart is to move faster on the ground. So the ground is the one that should have energy added to it, if it was to model the situation of accelerating the cart/ground relative speed.

Even your own example of the car moving the earth confirms this.

So again, the energy is from the wind, if your reference point is the cart. The whole concept of the energy from the road is a total dogmatic fallacy.

 

[xxyyzz]

Now if that prop was so arranged that it acted as a sail on the wind, using the rotation to create an apparent wind, it could extract energy out of the wind.

In the video KeenEd posted in #308 the cart is strapped down to the treadmill, you can see the cart has a forward thrust.

Is it sailing?

 

[mikemonty]

Ubergeekian: "My statement was clearly using a frame of reference fixed to the cart. "

But that does not work either. As the intention of the cart is to move faster on the ground. So the ground is the one that should have energy added to it, if it was to model the situation of accelerating the cart/ground relative speed.

Even your own example of the car moving the earth confirms this.

So again, the energy is from the wind, if your reference point is the cart. The whole concept of the energy from the road is a total dogmatic fallacy.

Go get 'em Halfway!... Go Halfway!...

 

[Pierrome]

Ubergeekian: "My statement was clearly using a frame of reference fixed to the cart. "

But that does not work either. As the intention of the cart is to move faster on the ground. So the ground is the one that should have energy added to it, if it was to model the situation of accelerating the cart/ground relative speed.

Even your own example of the car moving the earth confirms this.

So again, the energy is from the wind, if your reference point is the cart. The whole concept of the energy from the road is a total dogmatic fallacy.

I've been offline for a while I hope I haven't lost touch with what's going on too much.

However, regarding taking energy from the road being a dogmatic fallacy.
It's all very well going on about this is not possible or that is not possible. But, really if you are an unbeliever, you need to explain what you see in the videos.
If you think they are faked, how are they faked?
If the experimenters are mistaken in some way, how are they mistaken?
Finally, and most importantly, why would they want to do all this experimentation on something that is theoretically impossible?
Please explain their motivation.

 

[Ubergeekian]

Ubergeekian: "My statement was clearly using a frame of reference fixed to the cart. "

But that does not work either. As the intention of the cart is to move faster on the ground. So the ground is the one that should have energy added to it, if it was to model the situation of accelerating the cart/ground relative speed.

So let me get this right. You're saying that you can see how the cart can use energy from the wind to travel faster than the wind, but not how it can use energy from the ground to travel faster than the ground?

So again, the energy is from the wind, if your reference point is the cart. The whole concept of the energy from the road is a total dogmatic fallacy.

The energy comes from the velocity difference between the wind and the ground. If you you an axis system attached to the ground, that difference appears as wind speed. If you use an axis system attached to the wind, that difference appears as the ground speed. If you use an axis system attached to the cart, you need to consider both speeds.

This is all terribly basic kinematics and dynamics, you know.

 

[snowleopard]

I can't believe there are still arguments about whether the energy comes from the wind or the ground.

When you clap your hands is the sound made by the right hand or the left?