Merged DDWFTTW in a “Real” Wind

[profpangloss]

Nope. It's incorrect. You are making the error that the IRF is "tied" to the earth when it is initially only indexed to it. When the earth moves "non-inertially" it is no longer valid as the index. Inertial reference frames once defined have to move "inertially" in space and clearly can't be tied to accelerated objects. Otherwise they are not inertial reference frames.

Have Michael C and I spelled that out clearly enough now that we can move on, or do you still not understand it?

Regards,

WindGrins

As far as the wind and the cart are concerned, the earth is an inertial reference frame. We are not here considering the sun and the moon and whatever else you may want to bring into this discussion to save the cart.

 

[windgrins]

Try not to go down the "Humberpath"!

As far as the wind and the cart are concerned, the earth is an inertial reference frame. We are not here considering the sun and the moon and whatever else you may want to bring into this discussion to save the cart.

It looks like now you are starting to understand. Just like Michael's "dropped ball" example, you don't get to pick and choose the pieces you like to say that COM and COE hold. They hold in closed systems in Inertial Frames of Reference. ("Inertial" being an important word here.)

At one of the previous posters noted, according to your argument nothing can move against the earth since that would violate COM. Since we believe COM is valid and we also believe things move on the earth, then the earth must be the object by which momentum is conserved with. Anytime something moves by reacting against the earth, then the earth moves minutely to maintain COM. So it would be appropriate to drop this silly line of reasoning that you think you have going.

You are starting to seem very "Humberlike" when you ignore the fundamentals.

Regards,

WindGrins

 

[humber]

If the velocity of the Earth changes, it changes in any inertial frame. You can't have acceleration in one inertial frame and not in another!

We can indeed use the Earth to define an inertial frame in which the Earth is stationary at moment x, but if the velocity of the Earth changes after moment x, the Earth will no longer be stationary in the frame that we have defined.

Then you will need to consider how the brick go to be above the ground. When you lift if, the Earth will move the other way, and be attracted back when you drop it. And that is called naive oversimplification, as expressed in the example you posted.
Dropped bricks do not move the Earth one iota.

 

[Michael C]

Why wouldn't it be? The earth is at rest and there is wind and cart moving. They are all that is moving in that frame. Whatever momentum and energy they have must be conserved. It is that simple.

Did you look at the example I linked to? If the Earth is always at rest in an inertial frame, how is momentum conserved when a ball bounces off the ground? Or how is momentum conserved when a car accelerates?

 

[drewid]

Windgrins - You can add COM to that list.

 

[jduffy77]

As far as the wind and the cart are concerned, the earth is an inertial reference frame.

More hilarity. pranggloss argues for his ground power nemesis without knowing it.

 

[humber]

More hilarity. pranggloss argues for his ground power nemesis without knowing it.

Really embarrassing to have the trial exposed as a joke, isn't it?
Attacking profpangloss about misunderstandings that led you to believe in a fetish, won't help raise the status of the cart.

Spork is always telling me that NALSA or NASA won't listen to me, but that is because nobody listens to him, so he needs a proxy.

 

[jduffy77]

Really embarrassing to have the trial exposed as a joke, isn't it?
Attacking profpangloss about misunderstandings that led you to believe in a fetish, won't help raise the status of the cart.

Spork is always telling me that NALSA or NASA won't listen to me, but that is because nobody listens to him, so he needs a proxy.

Humber, its obvious again. Pace yourself!

 

[profpangloss]

Did you look at the example I linked to? If the Earth is always at rest in an inertial frame, how is momentum conserved when a ball bounces off the ground? Or how is momentum conserved when a car accelerates?

It is quite easy; since the earth cannot move in response to the ball, the ball must bounce off of the earth with the same velocity and momentum it had when it hit the earth. The earth is NOT ALLOWED to move as it is the reference for all other motion.

 

[profpangloss]

It looks like now you are starting to understand. Just like Michael's "dropped ball" example, you don't get to pick and choose the pieces you like to say that COM and COE hold. They hold in closed systems in Inertial Frames of Reference. ("Inertial" being an important word here.)

At one of the previous posters noted, according to your argument nothing can move against the earth since that would violate COM. Since we believe COM is valid and we also believe things move on the earth, then the earth must be the object by which momentum is conserved with. Anytime something moves by reacting against the earth, then the earth moves minutely to maintain COM. So it would be appropriate to drop this silly line of reasoning that you think you have going.

You are starting to seem very "Humberlike" when you ignore the fundamentals.

Regards,

WindGrins

Once again, you are wrong! The earth is declared to be stationary and that is that! Now anything moving and here we are only considering the wind and the cart, must obey conservation of energy and momentum in this frame where the earth is stationary. If the wind loses momentum and/or energy, the cart must gain it and vice versa. The earth plays no role whatsoever except to act as a reference for the wind and the cart.

 

[Michael C]

It is quite easy; since the earth cannot move in response to the ball, the ball must bounce off of the earth with the same velocity and momentum it had when it hit the earth. The earth is NOT ALLOWED to move as it is the reference for all other motion.

That won't do. Look at the example I quoted. Momentum is a vector quantity, so if the direction of movement of the ball changes, its momentum changes. Since momentum is always conserved, the momentum of something else must also change. That something else is the Earth.

Here's another example:

Question 5:

"If a 5-kg bowling ball is projected upward with a velocity of 2.0 m/s, then what is the recoil velocity of the Earth (mass = 6.0 x 1024 kg)."​

Answer:

Since the ball has an upward momentum of 10 kg*m/s, the Earth must have a downward momentum of 10 kg*m/s. To find the velocity of the Earth, use the momentum equation, p = m*v. This equation rearranges to v=p/m. By substituting into this equation,

v = (10 kg*m/s)/(6*10²⁴ kg)
v = 1.67*10^-23 m/s (downward)

Another way to write the velocity of the earth is to write it as

0.0000000000000000000000167 m/s​

 

[jduffy77]

it is quite easy; since the earth cannot move in response to the ball, the ball must bounce off of the earth with the same velocity and momentum it had when it hit the earth. The earth is not allowed to move as it is the reference for all other motion.

roflmao

 

[profpangloss]

That won't do. Look at the example I quoted. Momentum is a vector quantity, so if the direction of movement of the ball changes, its momentum changes. Since momentum is always conserved, the momentum of something else must also change. That something else is the Earth.

Here's another example:

Question 5:

"If a 5-kg bowling ball is projected upward with a velocity of 2.0 m/s, then what is the recoil velocity of the Earth (mass = 6.0 x 1024 kg)."​

Answer:

Since the ball has an upward momentum of 10 kg*m/s, the Earth must have a downward momentum of 10 kg*m/s. To find the velocity of the Earth, use the momentum equation, p = m*v. This equation rearranges to v=p/m. By substituting into this equation,

v = (10 kg*m/s)/(6*10²⁴ kg)
v = 1.67*10^-23 m/s (downward)

Another way to write the velocity of the earth is to write it as

0.0000000000000000000000167 m/s​

NONE of your examples are relevant because NONE of them refer to the frame of reference where the ground is stationary, by decree, if you like. That is a perfectly legitimate and ofetn used method of analysis; you just play God and say the ground is stationary and everything else moves with respect to it. NONE of your examples have any relevance to that case.

 

[jduffy77]

NONE of your examples are relevant because NONE of them refer to the frame of reference where the ground is stationary, by decree, if you like. That is a perfectly legitimate and ofetn used method of analysis; you just play God and say the ground is stationary and everything else moves with respect to it. NONE of your examples have any relevance to that case.

As long as you take into account the acceleration imparted by the earth. Which you don't.

 

[profpangloss]

roflmao

I suppose that's all a fool can do when he does not understand the discussion. Try not to hurt yourself.

 

[drewid]

Then you will need to consider how the brick go to be above the ground. When you lift if, the Earth will move the other way, and be attracted back when you drop it. And that is called naive oversimplification, as expressed in the example you posted.
Dropped bricks do not move the Earth one iota.

Now hang on. Let me call Newton and tell him he's wrong.


Sorry but that's a Stundie nomination.

 

[profpangloss]

As long as you take into account the acceleration imparted by the earth. Which you don't.

There isn't any unless you mean gravitiational acceleration but that does not factor into the two body collision of wind and cart in any significant way.

 

[jduffy77]

I suppose that's all a fool can do when he does not understand the discussion. Try not to hurt yourself.

That's something we agree on. I really believe it might be possible to laugh too much. "ball must bounce off of the earth with the same velocity and momentum it had when it hit the earth". Stop its too funny.

 

[jduffy77]

There isn't any.

And now we're back at your basic disconnect from reality. You can't have it both ways.

 

[profpangloss]

That's something we agree on. I really believe it might be possible to laugh too much. "ball must bounce off of the earth with the same velocity and momentum it had when it hit the earth". Stop its too funny.

It is funny that you can't understand that, yes.