Merged DDWFTTW in a “Real” Wind

[Dr. Keith]

You don't understand RMS or fluid dynamics, but unlike Jamie, are unwilling to accept that knowledge counts, and have no interest in learning.

I have a very keen interest in fluid dynamics and would really like to get a better handle on what you are trying to say in this part of the discussion, ie balloons traveling at WS.

Could you describe what moves at WS in a steady wind?

-neutrally buoyant balloons?
-suspended solids? (Ie dust particles)
-gases?
-air particles?

If not, then what is WS?

I really can't help but think we are talking past each other.

 

[mender]

Not even the medium?

Not at any of the seances humber's been to, and he attends many.
He's trying to contact Newton and Galileo to tell that they were wrong.

 

[mender]

Energy is not the only property which is conserved; momentum is conserved too. After their inelastic collision, the missiles (or at least the centre of gravity of their debris) is not moving in the 600 vs 600 mph example but it is moving (to the left, at 600 mph) in the 0 vs 1,200 mph example.

Fify.

 

[humber]

Fify.

Shot down.

 

[Jack by the hedge]

Fify.

Thank you.

 

[jduffy77]

If there is a closing speed of 1200 mph, any combination of speeds that add up to 1200 will produce exactly the same effect on the objects when the objects collide. 600 + 600, 0 + 1200, 376.9 + 823.1, etc; every one is the same to the objects, the only thing changing is the speed of the observer relative to the objects and since the observer isn't involved, that can't affect what happens to the objects.

He's not wrong about Jamie being wrong. is obviously wrong, as it equates a car and a wall. Two cars crashing head on at 50 mph is the same as one car crashing into another at 100 mph. One car crashing into a wall at 100 mph is the same as a car and a wall crashing head on at 50 mph. More or less, that is; the speed of the road relative to the cars will have some minor effect.

I am confused now. To go back to the original example. 1st car 600 head on into 2nd car at 600. 1st car at 1200 into wall at 0. You are saying the collision is the same for the 1st car in both scenarios. I was saying it is different. Correct?

 

[Jack by the hedge]

Shot down.

I made an error, which I withdraw, and I apologise for any confusion caused.

I am grateful for the correction.

(Do you see how easy that is?)

PS Would you like to comment on the substance of the post, after you get over gloating at my arithmetical slip?

 

[Jack by the hedge]

I am confused now. To go back to the original example. 1st car 600 head on into 2nd car at 600. 1st car at 1200 into wall at 0. You are saying the collision is the same for the 1st car in both scenarios. I was saying it is different. Correct?

Definitely different.

A car crashing into an identical car, both travelling at 60 mph in opposite directions is similar to one car travelling at 120mph hitting a static, identical car. It's also similar to a car hitting an unyielding barrier at 60mph.

The two cars hitting head on make an absolutely symmetrical impact - neither pushes the other back, they meet in the middle and stop or bounce off to some degree. So if you imagine the barrier is a massive wall of polished steel, you could watch the car and its reflection crash into each other in an exact mimic of the two car crash.

Does that help?

 

[jduffy77]

Definitely different.

A car crashing into an identical car, both travelling at 60 mph in opposite directions is similar to one car travelling at 120mph hitting a static, identical car. It's also similar to a car hitting an unyielding barrier at 60mph.

The two cars hitting head on make an absolutely symmetrical impact - neither pushes the other back, they meet in the middle and stop or bounce off to some degree. So if you imagine the barrier is a massive wall of polished steel, you could watch the car and its reflection crash into each other in an exact mimic of the two car crash.

Does that help?

Help who? You have just said what I have been saying all along. I read Mender's original post as saying something different.

 

[Jack by the hedge]

Help who? You have just said what I have been saying all along. I read Mender's original post as saying something different.

Well it was intended to help you, as it seemed to me you were right, but I hadn't seen mender make a mistake. I didn't think that was what you'd been saying all along, as you originally questioned mender's assertion that a 600 + 600 mph impact would have the same effect as a 0 + 1200 mph impact or any other combination that added up to 1200 mph. Maybe I need to go back and read what everyone said again.

Above, I said that a 60 + 60 mph impact would be the same as a 120 + 0 impact. That appears to be stating the same principle, doesn't it?

(I also said that a 60 + 0 impact could mimic it if one of the objects was not a car at all but rather a perfectly rigid, immovable barrier. That makes it a different case from two identical objects impacting.)

 

[humber]

While Googling for Rhett I came across another link which I hope one of you will critique.
http://warp.povusers.org/grrr/collisionmath.html

While looking for straws to clutch....

A quote from this link happens to be exactly how I initially thought about the collisions.
"So we have two forces: Vehicle 1 applies the equivalent of 50 km/h times its mass to vehicle 2, and vehicle 2 applies an equal force to vehicle 1. This causes both vehicles to stop right there

As if the rider, "you initially thought", added weight

That above refers to momentum, m*v. Momentum is conserved, energy is conserved, KE is not.

Where would the additional 50 km/h times the mass of the vehicle come from? Vehicle 1 cannot apply that force to itself. It's applying it to vehicle 2. So where is it coming from?

F = ma.

The answer is that it's not coming from anywhere because the force applied to vehicle 1 is not 100 km/h times the mass, but only 50 km/h times the mass. The same as with the rock wall."

Walls don't have momentum, m*v, when v = 0

Top reference from shouty-crank.com
http://warp.povusers.org/grrr/index.html

"The most prominent and severe case which I have seen was Jamie Hyneman from the show MythBusters getting this exact problem wrong in their "demolition derby special" episode, where he stated that two trucks travelling at 50 mph each and colliding head-on were subject to a collision force equivalent to hitting a rock wall at 100 mph. Maybe he is not a phycisist, but nevertheless he of all people should know this.

The correct answer is: The two collisions are completely equivalent."

He is "wrong" because he says they are the same, and genius corrects him by saying they are the same.


"From the point of view of one of the vehicles it makes absolutely no difference whether it hits a rock wall at 50 km/h or another identical vehicle which was traveling at the same speed in the opposite direction. The amount of force applied to the vehicle is the same in both situations"

Errr..no. One force, is a reaction to the other ( Newton)

It is a basic logical error, to say that because the forces one each are equal, in both situations ( car to car) and (wall to car) that they are of the same magnitude.

This clown is one of those who say "most people/physicists get this wrong"
No chump, it's you. Definitely you.

"(Ok, in reality there will be some differences because the consistency of a rock wall is very different from a consistency of a vehicle, but this only means that hitting the rock wall will be more severe than hitting the other car, although probably not by a lot.)"

That passage means "I think I can tell physicists when they are wrong, but don't know much else"

Force is a product of impact time. Basically F= ma = m*dv/dt
There is more. Elasticity, rotation, all sorts of stuff this bozo knows nothing about.

 

[humber]

Well it was intended to help you, as it seemed to me you were right, but I hadn't seen mender make a mistake. I didn't think that was what you'd been saying all along, as you originally questioned mender's assertion that a 600 + 600 mph impact would have the same effect as a 0 + 1200 mph impact or any other combination that added up to 1200 mph. Maybe I need to go back and read what everyone said again.

He got it wrong. Spork made has made the same mistake several times.

Above, I said that a 60 + 60 mph impact would be the same as a 120 + 0 impact. That appears to be stating the same principle, doesn't it?
(I also said that a 60 + 0 impact could mimic it if one of the objects was not a car at all but rather a perfectly rigid, immovable barrier. That makes it a different case from two identical objects impacting.)

No, TAD are not scientists or engineers, but seat-of-the pants opinionated.

Spork would not rise to defend his balloon claim, and none of you were willing to back him. He loses by default
The KE claim is wrong, as is the TM transform.
Drs Kammen, Rhett, Whiteman and Camp are correct.

 

[jduffy77]

Well it was intended to help you, as it seemed to me you were right, but I hadn't seen mender make a mistake. I didn't think that was what you'd been saying all along, as you originally questioned mender's assertion that a 600 + 600 mph impact would have the same effect as a 0 + 1200 mph impact or any other combination that added up to 1200 mph. Maybe I need to go back and read what everyone said again.

Above, I said that a 60 + 60 mph impact would be the same as a 120 + 0 impact. That appears to be stating the same principle, doesn't it?

(I also said that a 60 + 0 impact could mimic it if one of the objects was not a car at all but rather a perfectly rigid, immovable barrier. That makes it a different case from two identical objects impacting.)

I guess my English comprehension is the problem because it seems like you just contradicted yourself.

If there is a closing speed of 1200 mph, any combination of speeds that add up to 1200 will produce exactly the same effect on the objects when the objects collide.

As far as I can see this statement is clearly wrong but I will just leave it at that. I don't really think Mender is wrong so I must not understand his semantics.

 

[Dr. Keith]

I have a very keen interest in fluid dynamics and would really like to get a better handle on what you are trying to say in this part of the discussion, ie balloons traveling at WS.

Could you describe what moves at WS in a steady wind?

-neutrally buoyant balloons?
-suspended solids? (Ie dust particles)
-gases?
-air particles?

If not, then what is WS?

I really can't help but think we are talking past each other.

So, not having addressed the balloon at WS, nobody having any interest in the table cloth conundrum, we have moved on to the bombs in opposition.

Humber, care to address the balloon?

 

[Jack by the hedge]

"From the point of view of one of the vehicles it makes absolutely no difference whether it hits a rock wall at 50 km/h or another identical vehicle which was traveling at the same speed in the opposite direction. The amount of force applied to the vehicle is the same in both situations"

Errr..no. One force, is a reaction to the other ( Newton)

Which forces do you have in mind here? Also, in what way does it explain why you think the two scenarios would affect the car differently?

 

[humber]

Hey look, ynot found a link and tried to cherry pick it to.... see if he could make "spork and company" look bad.

I think it can be definitely said that no assistance is necessary.

1) There is no "spork and company". There is spork and JB. We're two different people. He can't seem to understand that (or is he just dishonest).

Just a TAD of a difference.

2) It doesn't make us look bad.

Q.E.D

 

[humber]

Which forces do you have in mind here? Also, in what way does it explain why you think the two scenarios would affect the car differently?

You have been told and proven to be wrong. End.

 

[humber]

So, not having addressed the balloon at WS, nobody having any interest in the table cloth conundrum, we have moved on to the bombs in opposition.

Humber, care to address the balloon?

I have won the balloon matter, hands down. Spork has not been able to defend it, just floated it.

He has lost that one.

You may carry on believing what you like.

 

[jduffy77]

I have won the balloon matter, hands down. Spork does not have the capacity to defend it, just float it. End.

Actually you have not said a single coherent thing about the balloon matter.

 

[Jack by the hedge]

As far as I can see this statement is clearly wrong but I will just leave it at that. I don't really think Mender is wrong so I must not understand his semantics.

I guess I can't see what you can see that makes it wrong.

It doesn't specify that the objects need to be the same objects in each scenario. Maybe that's too obvious. All he's saying is that it's the closing speed between the two objects that matters, and the relative velocities compared to some other frame of reference don't matter. If you don't change the speed of impact (and you don't change the objects) the result will be the same.