In the late 70s, my dad went down to an auto wrecker and bought 2 Fiat 128s (a '76 and a '77 or similar), which the Lada always reminds me of. One had a completely obliterated front end, the other a destroyed rear end. He cut both in half, welded the good parts back together, and my mom drove it until the late 80s, when he rebuilt a year-old Ford F350 that my mother only allowed if he bought her a complete, undamaged car. The damn thing is still toodling around town somewhere...

This thread has gotten me very curious to try all these things out for myself.

As far as equally weighted particles go, what you describe is not what we observe. We always see the same number of particles leave as came in, no matter their total momentum. A single particle going 1m/s ejects one particle also going 1m/s (I'm talking in ideal terms). A single particle going 2m/s doesn't release two particles going 1m/s, just one going 2m/s. The same particle going 100m/s likewise doesn't release 100 particles going 1m/s, nor 50 going 2m/s nor any other combination. As the force passes through the stationary particles, there's nothing to say what the mass or velocity of the striking particle was, just what the product of those two things was.

As for different sized particles, not having seen this done, if a solid (I mean a single piece, or welded together) 2kg particle came in at 1m/s, I predict a single 1kg particle would be ejected at 2m/s. My reason is the same as above: that when one ball strikes, the only information transmitted through the stationary particles is the total amount of force, not the velocity or mass of the striking object. Thus, the force transmitted through the stationary particles would be identical whether a 1kg ball struck at 2m/s or a 2kg ball struck at 1m/s. All this force is transmitted into the last ball which leaves with the same amount of force in the form of velocity as a factor of its mass, whatever that may be.

I think fusing the two balls together would fundamentally change their behaviour. I think when two loose balls hit together, the first one hits the stationary ones, bounces back towards the second ball which then stops, sending a second shock wave through the stationary particles, thus sending two signals very close together, and releasing two particles out the other side.

To continue the thought experiment, what if it were a 1.2kg particle striking a row of 1kg balls? I think it would be one particle going out at 1.2m/s, rather than 1 particle at 1m/s and a second at 0.2m/s or two of them together at 0.6m/s.>> ^heathen:

As you said momentum is mass velocity, and force is mass acceleration.
It's the mass of the particles entering that determines the mass of the particles leaving.
As the balls in a Newton's cradle all have equal mass it's tempting to restate that as the number of particles rather than the mass of the particles.
However if you designed a cradle to have four 1kg balls and one 2kg ball then swinging the 2kg ball would cause two 1kg balls to be displaced. (The same effect as taping or gluing two 1kg balls together.)
In a normal Newton's Cradle the acceleration, due to gravity, is constant.
The constant mass and constant acceleration cause the predictability, as the only energy lost is to air resistance and other negligibles such as sound or minimal compression of the balls on impact.
The forces introduced by the magnet scale inversely with distance, making the outcome a lot more unpredictable.

That's not just mesh. That's more like security bar fencing. My guess is someone well-meaning but without much mechanical intelligence thought it would be strong enough for cars to drive over, and better than an open hole, so they welded it to a cylinder that happened to fit and poof, instant manhole cover. Either way, that's an engineering *fail.

>> ^Asmo:

>> ^EMPIRE:
I don't know what you're thinking, but I'm thinking someone placed that metal mesh over the hole so that cars could go over the hole, but the mesh actually got caught in the hole, and levered the car up.

Umm, the video makes it pretty clear.
The front left tyre goes in to the hole, smashes in to the far side and the ass end of the car rises as the front dramatically decelerates...

Nope. Watch the second video (in eric3579's post above) on 720p and you can better see what happens.

The manhole has an off-center metal mesh cover welded to a cylinder that fits down into the manhole (presumably to keep the mesh in place).
The front-left tire clips the side of the mesh cover, presumably just enough to pop it up. That's what catches the undercarriage and vaults the back end up.
The structure of the mesh-cylinder apparatus is more apparent at the end of the video when it settles near the hood of the vehicle.

I'm not going to dive down the rabbit hole of researching this right now, but the wiki page for Helium seems to agree with me (extraction from natural gas is done,
and entertainment balloons aren't noted as a major user.

It does however note that entertainment balloons are a waste made possible by artificially low prices. These artificial low prices for helium grades probably mean many natural gas producers simply vent it away, which will change as the commodity rises in price.

>> ^deathcow:

>> ^bamdrew:
I'm very, very skeptical that party balloon use is the major user of helium gas. Sure, its "wasted" on entertainment, but there are industrial uses for large amounts of helium (MIG welding and such).

ALSO, I was under the assumption that Helium can be pulled down from natural gas production (if there is money in it).

Dunno, think about the MASSES of people with balloons. Sure someone is welding in every city, but balloons are just everywhere.

>> ^bamdrew:

I'm very, very skeptical that party balloon use is the major user of helium gas. Sure, its "wasted" on entertainment, but there are industrial uses for large amounts of helium (MIG welding and such).

ALSO, I was under the assumption that Helium can be pulled down from natural gas production (if there is money in it).


Dunno, think about the MASSES of people with balloons. Sure someone is welding in every city, but balloons are just everywhere.

I'm very, very skeptical that party balloon use is the major user of helium gas. Sure, its "wasted" on entertainment, but there are industrial uses for large amounts of helium (MIG welding and such).


ALSO, I was under the assumption that Helium can be pulled down from natural gas production (if there is money in it).

Man, I am always impressed with these kinda things. Especially when the guy says "I used some argon from my welding kit" as if he was talking about a hammer.

Needs a drop of JB WELD

Because those pieces are probably stamped not poured. Stamping makes the metal much stronger than an equivalently molded piece.

>> ^rottenseed:

Why wouldn't you just make a mold that makes that whole piece?

As per wikpedia :

Benefits

The combination of fast joining times (on the order of a few seconds), and direct heat input at the weld interface, yields relatively small heat-affected zones. Friction welding techniques are generally melt-free, which avoids grain growth in engineered materials, such as high-strength heat-treated steels. Another advantage is that the motion tends to "clean" the surface between the materials being welded, which means they can be joined with less preparation. During the welding process, depending on the method being used, small pieces of the plastic metal will be forced out of the working mass (flash). It is believed that the flash carries away debris and dirt.

Another advantage of friction welding is that it allows dissimilar materials to be joined. This is particularly useful in aerospace, where it is used to join lightweight aluminum stock to high-strength steels. Normally the wide difference in melting points of the two materials would make it impossible to weld using traditional techniques, and would require some sort of mechanical connection. Friction welding provides a "full strength" bond with no additional weight. Other common uses for these sorts of bi-metal joins is in the nuclear industry, where copper-steel joints are common in the reactor cooling systems; and in the transport of cryogenic fluids, where friction welding has been used to join aluminum alloys to stainless steels and high-nickel-alloy materials for cryogenic-fluid piping and containment vessels.

Friction welding is also used with thermoplastics, which act in a fashion analogous to metals under heat and pressure. The heat and pressure used on these materials is much lower than metals, but the technique can be used to join metals to plastics with the metal interface being machined. For instance, the technique can be used to join eyeglass frames to the pins in their hinges. The lower energies and pressures used allows for a wider variety of techniques to be used.

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

http://www.mtiwelding.tv/videos/index/31

In reply to this comment by rottenseed:
Why wouldn't you just make a mold that makes that whole piece?

>> ^HenningKO:

Man, that sure is an effective way to stick together whatever those two things are.


You can't tell what that is? It's a wheel.

>> ^shagen454:

The first time I watched this I wanted to say something perverted, I was a little tipsy so I put it off. Now I'm watching this a second time and I'm still thinking the same thing... thinking I should just put the observation off. Haha!


And now I'm intrigued! I have to know...

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