No, I understand that. It is true by definition. But it is not the case that the law of conservation of momentum is true by definition, and this law doesn't hold in that reference frame because that reference frame is not inertial.
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Merged DDWFTTW in a “Real” Wind
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No, I understand that. It is true by definition. But it is not the case that the law of conservation of momentum is true by definition, and this law doesn't hold in that reference frame because that reference frame is not inertial.
Because the earth experiences a force on it from the cart, and it accelerates in response to this force.
On the question of the change (or not) in the earth's momentum, there are two distinctions that must be made: that between a closed system and an open system, and that between an inertial reference frame and a noninertial reference frame.
Conservation of momentum does not hold in an open system, even with respect to an inertial reference frame, and it does not hold with respect to a noninertial reference frame, even in a closed system.
profpangloss wants to use a reference frame in which the earth is, and remains, stationary, and he wants to consider this reference frame to be practically inertial, that is, he wants to ignore the very small change in the earth's velocity. We can do this, provided we consider the earth to be external to our system. So our system consists of the cart and the air alone, but not the earth. I think this also accords with profpangloss's intuition. So far, so good. But we cannot ignore the fact that the earth exerts a force on the cart. This force acts on our system from outside it. Therefore, our system is not closed, and the momentum of our system is not conserved, but rather changes in response to the external force on it.
On the other hand, if we want momentum to be conserved, we need to consider a closed system, i.e., a system that is free from external forces. We want the cart to be part of our system, and the cart experiences a force from the earth, so the earth must be part of our system too. If we include the earth in our system, along with the cart and air, the system is closed and momentum is conserved. But, if we do things this way, we cannot treat the earth as absolutely stationary. Rather, we must choose a reference frame which is more nearly inertial than even the earth, and allow the momentum of the earth to change, with respect to this reference frame, in response to the force of the cart on the earth.
Conservation of momentum does not hold in an open system, even with respect to an inertial reference frame, and it does not hold with respect to a noninertial reference frame, even in a closed system.
profpangloss wants to use a reference frame in which the earth is, and remains, stationary, and he wants to consider this reference frame to be practically inertial, that is, he wants to ignore the very small change in the earth's velocity. We can do this, provided we consider the earth to be external to our system. So our system consists of the cart and the air alone, but not the earth. I think this also accords with profpangloss's intuition. So far, so good. But we cannot ignore the fact that the earth exerts a force on the cart. This force acts on our system from outside it. Therefore, our system is not closed, and the momentum of our system is not conserved, but rather changes in response to the external force on it.
On the other hand, if we want momentum to be conserved, we need to consider a closed system, i.e., a system that is free from external forces. We want the cart to be part of our system, and the cart experiences a force from the earth, so the earth must be part of our system too. If we include the earth in our system, along with the cart and air, the system is closed and momentum is conserved. But, if we do things this way, we cannot treat the earth as absolutely stationary. Rather, we must choose a reference frame which is more nearly inertial than even the earth, and allow the momentum of the earth to change, with respect to this reference frame, in response to the force of the cart on the earth.
I think you are right, but if we use correct analytical techniques, we will find our theories concord with the demonstrated physical reality, ie, the cart works. This is unacceptable to some people, therefore they must continue to propose invalid models based on incorrect hypotheses to try to expose what to them seems like a terrible hoax and fabrication.
I find it quite interesting that there exist subsets of successful analysis even within the grossly incorrect theories they use. For them, the world is full of incongruous "outliers" of phenomena, must be pretty scary.
I see it this way. If NALSA scrap the record, some influential people will have to admit to being easily fooled.
Now, who would readily accept that? Conned by a moron?
However, he still has the TM hurdle, and that one is incandescently funny.
ThinAirDesigns
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We've known for years that CrisMyevShroldprof doesn't even know what an inertial frame is.
In spite of all common and readily available knowledge, imagine ignorantly and stubbornly holding to the position that one can declare an object whose velocity is constantly changing (earth) as a true inertial frame.
Sad.
JB
In spite of all common and readily available knowledge, imagine ignorantly and stubbornly holding to the position that one can declare an object whose velocity is constantly changing (earth) as a true inertial frame.
Sad.
JB
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That is right, but you are dealing with cult members watching their trial go up in obvious smoke, so will look for the smallest gap to hide in.
Let them have the momentum transfer of objects striking the ground for example, and then leave them to explain why that would make a difference to the cart.
He is right, and you will still have the TM to explain. The magical TM that has a propless cart in the shape of a cow.
Winnowing the chaff for the smallest of grain. Whining at NALSA to be allowed to take it over.
Not like the image is it?
Ground power.
Humber, careful, you are lying again.
Bring the Rose Water. NALSA, may cave in, who knows? But as I said, I have prepared for that.
Once again, defeated, no matter how much or many he recruits.
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The vane stalled, and that is can be easily calculated...but not by you.
I was started when the wind was 50 degrees off ddw. It does speak of bias.
I have cleaned it up so all the noise is removed. It would makes Jenkins' record look shaky, if that lax result were accepted. Constantly relying on the kindness of strangers has its drawbacks.
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When you say defeated what do you mean exactly? Will there be any visible manifestation of the defeat or will it just be in your mind?
Of course. There is no energy transfer to the Earth as a whole. For one thing, it's elastic. For a dropped brick to move the Earth, the other side of the planet would need to instantly move. The examples from Michael_C, are as always, taken from simplified cases for the general public consumption, and where objects are treated as points.
When large highways were built, many Carteers of the time gave dire warnings that traffic would change the Earth's spin, and wanted the flow to be alternated in compensation.
The only energy imparted to the ground is via local work of deformation of the soil, but again let them have the transfer.
Using the centres of mass as frames of references, the cart and Earth are both at rest.
From that frame, the cart moves, and gains momentum, p, and so KE of p^2/2mcart.
The earth moves, and gains -p, so KE of p^2/2mearth
The sum of the energy
(p^2/2mcart+ p^2/2mearth), must come from the wind, with p^2/2mearth being transferred to the ground. But the Earth is massive, so that amount is tiny, leaving p^2mcart to be extracted from the wind.
Always trying to read the tea leaves.
Humber this is gibberish. Why don't you try and think about what you want to say and re-post.
Is it? See if you can find fault without contradicting yourself.
Jack by the hedge
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Amusing. Evidence?
Initially the transfer of energy only causes local deformation, since the planet is not infinitely rigid, but the energy disperses through the planet. Most gracious of you, I'm sure, to "let" nature's laws have their way.
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