Down wind faster than the wind

[humber]

Problem A: 10kg mass moving at 1m/s strikes a 1kg stationary mass. If the collision is inelastic, the combined 11kg mass (calculated using conservation of momentum) continues moving at (10*1+1*0)/11 = about .91m/s. For the observer that was also moving at 1m/s, the collision mass is now moving at a relative velosity of 1-.91 = 0.09m/s. The initial kinetic energy (1/2 mv²) was 5 joules and the final ke is about 4.55 joules. The missing .45 joules was converted to heat.

Problem B: A 10kg stationary mass is struck by a 1kg mass moving at 1m/s. Agian, for and inelastic collision, the combined mass moves at (10*0+1*1)/11 = about 0.09m/s relative to the observer that was not moving. The kinetic energy was initially 10*0*0/2+1*1*1/2=0.5 and after the collision is 11*(0.09)²=0.05 joules again leaving 0.45 joules converted to heat.

To the observer, both collisions looked exactly the same. If you want, you can try the calculations for an elastic collision. In this case, the kinetic energy is conserved instead of being converted into heat.

I thought a bit before answering this, but I don't know if you could be more obtuse, Dan O.
Momentum is conserved, right? So the sum the momentum in one case is 10 times that of the other? Redistribute at collision time. There you go.
The fact that the final velocities of the combined masses are different doesn't matter, as long as the observer is satisfied concerning the relative velocities? They are different events, as events. You also have the observer "following" one mass or the other.

The collision is some thing that happens in the journey of the objects, there is no start or finish. There is no prior expectation of a result.
It is not a problem of maths, but of "the world" I really don't know why you make any distinction. Should those masses carry on, they may hit the surface of the planet with different effect. They have same mass but different initial velocities as they approach.

The collision happens. The observer can only ever witness it.
Collisions involve a larger level of momentum. They are different.
The effect will be manifest in the world. Stuff happens independently of the observer. Everything is relative, you say, but you impose an arbitrary observer?
Annihilation of a small mass at impact releases more energy than a little on of the same velocity. Observer or not.
Is this why you thing that there is a wind? That the nature of the objects and how they react can simply be abstracted to simple one-off events?
I notice this in this thread. Tests and machines are analysed from the middle, or some place of convenience.
Many magnetic over-unity devices forget the history of ,say, a steel ball.
They think only of it being pulled towards the magnet, but if they don't do exactly that again, then all is forgotten. It's free.

 

[humber]

humber:


I am a all powerful. The cart bends to my will. I ROCK!!!!

JB

OK JB. How can the cart move faster than the hand? Over time, it must move away, otherwise both will always be the same velocity. That of the hand, I expect. Get him to do it pushing with a constant velocity source, and not a hand. It is a simple deception.
These devices exist in industry, where an extension is required to move faster than a slider. Some old looms for example, but of course they are reset before reuse.

 

[humber]

Yes they are. Velocity is meaningless except as defined as a change in velocity. The energy term is ACCELERATION not velocity. Velocities may differ in reference frames with no energy loss, all measurements in all frames will give you the same laws.

Darwinian elimination for you on board the battleship, then.

 

[spork]

how freakin' long do you need to see it running before you figure out that it's not running on stored energy?

Of course it's running on stored energy - the energy stored in the coal that's burned at the power plant, that powers our treadmill.

As far as tests and videos go, I'm kind of feeling like we've passed the point of diminishing returns. We made a lot of videos showing just about everything we can think of. We posted a number of videos upon direct request of skeptics. At this point I'm not too keen on posting any more videos unless they meet one of these two requirements:

1) They're dead simple to do (no pullies, weights, or duct tape)

or

2) They actually demonstrate something we missed. Something that could reasonably prove we didn't fake it, or that there's not some reasonable explanation for what's happening.

Next we'll be performing test to satisfy humber that it's not powered by the vibration energy given by string theory. Frankly I don't want to convince anyone that bad. In point of fact, I think we still need a few skeptics if we want the Mythbusters to do a segment. Then they can start getting the hate mail.

 

[Dan O.]

I am through trying to explain physics to humber. I'm just going to put him on ignore and pretend he doesn't exist.

 

[humber]

You're clamouring to Spork about giving evidence, but you won't even try a simple experiment yourself to test your theories?

That is such a tired line, Michael_C.
You tell me how it is possible for the hand to remain on that cart, but the cart not move away if it has a higher velocity?
It is impossible, so I am not going to test it.

What you don't see, is that the user will have to move forward when his arm becomes fully extended. Then what?

 

[spork]

He is playing a trick, by operating his hand in a similar way as the cart extends itself, but the movements are small, so you don't notice..

Now we're getting into faked moon landing/9-11 consipiracy territory.

If only there were some way to prove this for ourselves. I wonder if anyone's posted the parts and build instructions on the internet? Maybe we could borrow one of these devices and try it ourselves. Naw - spewing bullsh!t on-line is both easier and more fun.


EDIT: I was down at AeroMicro today getting a new prop and wheels for my latest cart, and Perry told me they had another guy in there the other day buying parts to make one. Whoever you are - good for you.

 

[humber]

Of course it's running on stored energy - the energy stored in the coal that's burned at the power plant, that powers our treadmill.

As far as tests and videos go, I'm kind of feeling like we've passed the point of diminishing returns. We made a lot of videos showing just about everything we can think of. We posted a number of videos upon direct request of skeptics. At this point I'm not too keen on posting any more videos unless they meet one of these two requirements:

1) They're dead simple to do (no pullies, weights, or duct tape)

or

2) They actually demonstrate something we missed. Something that could reasonably prove we didn't fake it, or that there's not some reasonable explanation for what's happening.

Next we'll be performing test to satisfy humber that it's not powered by the vibration energy given by string theory. Frankly I don't want to convince anyone that bad. In point of fact, I think we still need a few skeptics if we want the Mythbusters to do a segment. Then they can start getting the hate mail.

I don't say it runs on stored energy. It simply takes more from the belt.
The only mystery is why anyone would be surprised that it can travel up a belt.
Lost of videos of the belt, but no convincing wind tests. The street demonstration is not proof of anything other than the cart moves in the wind at some indeterminate speed.

 

[spork]

I thought a bit before answering thisl...

What!!! You don't change the whole game plan at half time. Stick with your strengths man!

 

[humber]

Now we're getting into faked moon landing/9-11 consipiracy territory.

If only there were some way to prove this for ourselves. I wonder if anyone's posted the parts and build instructions on the internet? Maybe we could borrow one of these devices and try it ourselves. Naw - spewing bullsh!t on-line is both easier and more fun.


EDIT: I was down at AeroMicro today getting a new prop and wheels for my latest cart, and Perry told me they had another guy in there the other day buying parts to make one. Whoever you are - good for you.

I was referring to the two skateboard device.

Do you feel that you have to test what is very simply analyzed ?

Same challenge. Please explain how over a distance, that the hand can remain in contact if the device, if it is traveling faster than the hand? After one minute, where will the hand be, and where will the cart be?

 

[humber]

That's too easy.
How can I tell if the astronaut hit the spaceship or vice-versa?

It depends upon my knowledge of the history of the objects. If I am a "suddenly" free-floating observer, and I see them moving towards each other, there is no question. It is moot. They hit each other.

On the other hand, if they are in my view but a fixed distance apart, then I can tell by various means. They are both fixed in my "frame" so I can see what is happening of course, but I could use other means.
For example, how much energy was required to achieve the velocity at impact?

I could apply the same forces to each, for the same time. If force is applied to the astronaut, then the velocity at impact will be greater than if I had done the same to the space-station. Knowing the impact velocity and the masses, will allow me to infer which was which. If I can make a distinction, they are different. Time has an arrow, so I can do the same for objects that are moving by but closing in on each other. Then I can tell as well.
There is more information available than just velocity, and if I use only that, I get only part of the picture.

 

[humber]

What!!! You don't change the whole game plan at half time. Stick with your strengths man!

I will, and you stick with your weaknesses

 

[Michael C]

That is such a tired line, Michael_C.
You tell me how it is possible for the hand to remain on that cart, but the cart not move away if it has a higher velocity?
It is impossible, so I am not going to test it.

What you don't see, is that the user will have to move forward when his arm becomes fully extended. Then what?

Let's get this clear. The video we're talking about is here. there's a cart with a board on top of it. The hand is pushing the board. The board is pushing the cart. The hand and the board are moving at the same speed. The cart under the board is moving faster. Is this impossible, or not?

For the analogy with Spork's craft, replace "moving board" with "moving air".

 

[ynot]

When you say "of this type", I don't get it ... we've never started the device with a string before.



And now I'm completely confused. I thought you wanted us to *start* the machine using a string rather than the hand. Now your complaining about using a hand as a "stop". Starting the device with a string won't change the fact that something is going to have to "stop" the device when it get's to the top of the treadmill

I'm happy to do a test for you, but I'm not going to go out of my way until we both understand what you are actually want the test to be. Is this a "start" test, or a "stop test?



We already have videos posted where we show it rolling untouched for close to 2 minutes. I've asked you before and not received and answer - how freakin' long do you need to see it running before you figure out that it's not running on stored energy?




And you're going to keep awaiting them until I figure out what you wish to test. I'm not doing it ynot until you can tell me *exactly* how you want it set up, start to finish. This test is being done *only for you*, and performing a test that you then say "that wasn't what I wanted" is just a waste of time.

So, spell it out in its entirety and we'll chat about setting it up.

JB

Fair enough. When you say a video “where the cart rolled for two minutes untouched” I guess you mean the one were the moving tread had a piece of flat wood placed under it? Sorry but I consider this a bogus test. You are not testing on a flat surface and you are running the cart with it’s wheels on either side a hump created by the board. The cart is essentially surfing with that hump. Don’t know why you didn’t just raise or lower one end of the treadmill.

It’s essential to ensure that the cart is always running on a flat surface and not too close to either end as there is always a slight bump in the tread close to each roller. Just the fact that the tread belt has a bump were it’s jointed could be also having some effect (not that this can be avoided). I also think your cart is unnecessarily light and should have some more weight added to it. Being so light exaggerates very small influences.

I would prefer the treadmill to have a slight uphill incline.

Don’t know what you mean by “start” and “stop”. the piece of string is a stop in that it stops the cart from going backwards (but allows it to go forwards). The hand in the video was used as a stop to stop the cart going forwards.

If your treadmill can be slowly accelerated up to speed then placing the cart on it before starting the treadmill would be the best. If not placing the cart on the moving tread as I have suggested would be okay.

What is being tested by this test is whether the thrust of the propeller that is greater than the rolling resistance can be sustained.

Is there anything else you need to know?

If you don’t want to do this test I will do it myself when my cart is ready (and several other tests I have planned).

 

[rehn]

Alrighty, here's your self start video. It's pretty darn unimpressive, but it does exactly as advertised.
http://www.youtube.com/watch?v=QTAd891IpRs&fmt=18

Thanks. I just want to verify one thing. The prop is rotating CV( from behind ), and if not connected to wheels it would rotate CCV. Correct Y/N ?

 

[spork]

I just want to verify one thing. The prop is rotating CV( from behind ), and if not connected to wheels it would rotate CCV. Correct Y/N ?

Correct.

 

[humber]

Let's get this clear. The video we're talking about is here. there's a cart with a board on top of it. The hand is pushing the board. The board is pushing the cart. The hand and the board are moving at the same speed. The cart under the board is moving faster. Is this impossible, or not?

For the analogy with Spork's craft, replace "moving board" with "moving air".

Yes, that's the one. I see what you see. But the advance must stop.

The bottom part must eventually fully extend itself, at which point the speed of the lower part will fall to the upper part, and so the hand.

It is done over the short term by adroit control of the hand and arm.
The velocity of the hand at the end will higher than at the beginning. It is just not noticeable.

Replace the hand with a fixed speed cart, and use it to push the device.
There may be an initial gain as the lower boards advances under the other, but over the long run, and to remain in contact, the two must travel at the same speed. If both continue to accelerate, the process may well continue, until the applied force limits the achievable velocity. All things being equal, this will be the same velocity as a device without the advance feature. The gain is transient. How else?

ETA:
Your track devices differ, because the gain will be spread over a longer time. (The time between 0V and V_max, assuming a constant force). Again same conditions, same force, will result in the same max velocity, gearing or not.

 

[Michael C]

Yes, that's the one. I see what you see. But the advance must stop.

The bottom part must eventually fully extend itself, at which point the speed of the lower part will fall to the upper part, and so the hand.

It is done over the short term by adroit control of the hand and arm.
The velocity of the hand at the end will higher than at the beginning. It is just not noticeable.

There's no need for adroit control of hand and arm. Whatever speed the hand moves, the cart moves faster. The advance will eventually stop because the board has a finite length. If the person doing the video had used a longer board, they could have made the cart go further. As long as the board continues to advance, and is in contact with the cart, the cart advances faster than the board.

It's the same with Spork's vehicle: as long as the air continues to move, and is in contact with the propeller, the vehicle advances faster than the air.

 

[H'ethetheth]

I'm a bit late to this cool, if somewhat ill-tempered thread. It took me a while to understand this thing.
This video illustrates my initial misunderstanding:

I initially thought that the direction of the propeller was set so that a tailwind would make it rotate in the direction that makes the wheels go forward. Only after the treadmill explanation I realised that it's the other way around. So the initial acceleration is not caused by the rotation of the propeller, but by the drag on the entire cart. As the cart speeds up the propeller provides less and less drag to the wheels and at some point starts providing net thrust.

For the people who share this misunderstanding (I think Humber is one of them), you can see this in action as the heavy gust of wind in the second run actually spins the prop the other way, which means the cart is actually skidding on wheels moving backward. Only when the prop gets less tailwind the wheels take over the driving of the prop.

Thanks for this really cool thread!

 

[Ivor the Engineer]

http://en.wikipedia.org/wiki/Elastic_collision

These equations may be solved directly to find v1 and v2. However, the algebra can get messy. A cleaner solution is to first change the frame of reference such that either v1 or v2 appears to be 0. The final velocities in the new frame of reference can then be determined followed by a conversion back to the original frame of reference to reach the same final result. Once either or is determined the other may be found by symmetry.

That can't be right, can it Humber?