I think ideally, as momentum must be conserved, that the ball would come in, the other ball would be ejected, and decelerated until it escaped the magnetic pull going the same speed as the incoming ball was before it started accelerating.

On a real physical track like this with friction and sound energy loss, I think the ball would be ejected, not overcome the pull of the magnet, and get sucked back pretty quick. It may strike hard enough to send the other ball out a bit, but after very few iterations, they would be all stuck together.

I haven't thought yet about the effect of the magnet moving towards the first ball as it approaches. Maybe this has no net effect at all.>> ^oritteropo:

Well it's only a guess, since I'm too lazy to do the calculations , but I don't think the kinetic energy from the impact would be sufficient to overcome the very large magnetic force, so click and no ball ejected.
>> ^messenger:
[...] Now I want to know what would happen if there was only one ball after the magnet. What do you think?

Well it's only a guess, since I'm too lazy to do the calculations , but I don't think the kinetic energy from the impact would be sufficient to overcome the very large magnetic force, so click and no ball ejected.
>> ^messenger:
[...] Now I want to know what would happen if there was only one ball after the magnet. What do you think?

I think that's what we would see. It also follows that the first ejected ball would leave with a much greater velocity than the second ejected ball as the second collision from the incoming ball would have been much smaller. Now I want to know what would happen if there was only one ball after the magnet. What do you think?>> ^oritteropo:
Based on that, I wonder if a slowmo of the ball in the original video might've shown that it bounced slightly before coming to rest?

Yes I found a reasonably clear explanation, and added it as a postscript to my earlier comment after you'd quoted it, but before I got the e-mail notification.
>> ^messenger:

[...]
If momentum = velocity mass, then doubling the velocity will double the momentum. Using the cradle, if you drop a ball from very very close to the first stationary ball, a single ball will move from the other side and move a very very short distance. If you then drop the ball from perpendicular, a single ball will move from the other side, and rise to (nearly) perpendicular. I have seen this much in my own observations. I don't think we need to do any calculations to understand that the impact velocity in the first essay is way less than half the impact velocity in the second essay (we don’t need exact numbers; we just need to know that the impact velocity is more than double). That means we have met your criteria for increasing the momentum to more than that of two balls at the first velocity, yet one ball still comes out.
A mental model to demonstrate my theory of “two particles in = two impacts = two particles out” is to imagine a bit of sponge between the last two balls in a Newton’s cradle. Pull the second ball out (which will push the first ball ahead of it) to a great enough height that the momentum of the outside ball’s impact is enough to completely squeeze the sponge and cause a second impact wave. The second ball would impact measurably later than the first, and before the ejected particle came back. Pretty clearly, two balls will emerge from the other side. This is what I think is happening on a micro scale when two independent balls are dropped together.

The cradle is better than the track because it allows for larger weights, where the track would require a denser material or hollow particles; but the track is easier for measuring incoming and outgoing force because on a steady grade, it’s simply a measure of distance, which is easy to capture roughly, even without a camera.

If momentum = velocity*mass, then doubling the velocity will double the momentum. Using the cradle, if you drop a ball from very very close to the first stationary ball, a single ball will move from the other side and move a very very short distance. If you then drop the ball from perpendicular, a single ball will move from the other side, and rise to (nearly) perpendicular. I have seen this much in my own observations. I don't think we need to do any calculations to understand that the impact velocity in the first essay is way less than half the impact velocity in the second essay (we don’t need exact numbers; we just need to know that the impact velocity is more than double). That means we have met your criteria for increasing the momentum to more than that of two balls at the first velocity, yet one ball still comes out.

A mental model to demonstrate my theory of “two particles in = two impacts = two particles out” is to imagine a bit of sponge between the last two balls in a Newton’s cradle. Pull the second ball out (which will push the first ball ahead of it) to a great enough height that the momentum of the outside ball’s impact is enough to completely squeeze the sponge and cause a second impact wave. The second ball would impact measurably later than the first, and before the ejected particle came back. Pretty clearly, two balls will emerge from the other side. This is what I think is happening on a micro scale when two independent balls are dropped together.>> ^oritteropo:

Thanks <img class="smiley" src="http://cdn.videosift.com/cdm/emoticon/smile.gif">
I was actually going to suggest that the first part of the experiment should be fairly easy to replicate, with a track and marbles or ball bearings or similar. Unless you have a constant grade the velocity (and therefore momentum) calculations will be a bit tedious, and it occurs to me that angular momentum may have some effect too, so perhaps a video camera and some marks on the track (or sensors and a microcontroller) to directly measure the velocity just prior to impact would be easier. To confirm or disprove my assertion you want to keep increasing the momentum of impact until it's more than the momentum of a two balls, and see what happens.
There are videos of a Newton's cradle type setup only with different sized balls, I might go looking tonight.
>> ^messenger:
That shoulda been @oritteropo too.

Thanks

I was actually going to suggest that the first part of the experiment should be fairly easy to replicate, with a track and marbles or ball bearings or similar. Unless you have a constant grade the velocity (and therefore momentum) calculations will be a bit tedious, and it occurs to me that angular momentum may have some effect too, so perhaps a video camera and some marks on the track (or sensors and a microcontroller) to directly measure the velocity just prior to impact would be easier. To confirm or disprove my assertion you want to keep increasing the momentum of impact until it's more than the momentum of a two balls, and see what happens.

There are videos of a Newton's cradle type setup only with different sized balls, I might go looking tonight.

p.s. Didn't find that one, but did find a good explanation of the one vs two ball collision issue in Newton's cradle:



Based on that, I wonder if a slowmo of the ball in the original video might've shown that it bounced slightly before coming to rest?
>> ^messenger:

That shoulda been @oritteropo too.

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.

>> ^messenger:

I know that multiple balls hitting one side will cause multiple balls to be released from the other side, but momentum isn't measured by counting the incoming particles; it's measured by mass velocity, and that's all. One ball hitting with great speed usually releases one ball at great speed out the other side. Two balls with very low speed, even with less total momentum than the single fast-moving ball, will release two balls from the other side at the same low speed. It's something about the number of particles, not their momentum, that determines how many are ejected.

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.

My own prediction was that one particle would come out the other side, be unable to escape the magnet, the magnet would pull it back, and the original particle would be sent back the way it came with equal speed, initially fast, then slow down and almost get back where it started. Oh well. That's why we have science.>> ^ghark:

that was brilliant, quite unexpected (for me at least)

I know that multiple balls hitting one side will cause multiple balls to be released from the other side, but momentum isn't measured by counting the incoming particles; it's measured by mass*velocity, and that's all. One ball hitting with great speed usually releases one ball at great speed out the other side. Two balls with very low speed, even with less total momentum than the single fast-moving ball, will release two balls from the other side at the same low speed. It's something about the number of particles, not their momentum, that determines how many are ejected.>> ^oritteropo:

Try splitting the beads in a Newton's cradle so there are more than one swinging in at the end, like this:
[embed removed]
It's not that the balls know anything in particular, it's that the momentum generated by a single ball is enough to dislodge an equal ball from the other end. In the case of the three balls, there is the right amount of momentum to dislodge three balls.
Now, when we have a magnet involved the single bead is accelerated towards the magnet at a great rate of knots imparting extra momentum so it's now equivalent to many balls (with just gravity) and the only thing stopping all the balls on the other side of the magnet flying off is that the same magnetic force is stopping the closer ones from moving.
>> ^messenger:
Love it, as with just about anything with Sixty Symbols.
I'd like to know why two balls broke off, rather than one, which is what happens in Newton's Cradle, no matter how hard to smack them. The row of particles has no way of knowing that the incoming particle was accelerated before it struck, so there must be something else at work here. I wonder if it's the incoming particle shifting the whole mass in the negative direction as it pulls on the magnet, and if the magnet were fixed in place if just one ball would move off.

Try splitting the beads in a Newton's cradle so there are more than one swinging in at the end, like this:


It's not that the balls know anything in particular, it's that the momentum generated by a single ball is enough to dislodge an equal ball from the other end. In the case of the three balls, there is the right amount of momentum to dislodge three balls.

Now, when we have a magnet involved the single bead is accelerated towards the magnet at a great rate of knots imparting extra momentum so it's now equivalent to many balls (with just gravity) and the only thing stopping all the balls on the other side of the magnet flying off is that the same magnetic force is stopping the closer ones from moving.
>> ^messenger:

Love it, as with just about anything with Sixty Symbols.
I'd like to know why two balls broke off, rather than one, which is what happens in Newton's Cradle, no matter how hard to smack them. The row of particles has no way of knowing that the incoming particle was accelerated before it struck, so there must be something else at work here. I wonder if it's the incoming particle shifting the whole mass in the negative direction as it pulls on the magnet, and if the magnet were fixed in place if just one ball would move off.

Love it, as with just about anything with Sixty Symbols.

I'd like to know why two balls broke off, rather than one, which is what happens in Newton's Cradle, no matter how hard to smack them. The row of particles has no way of knowing that the incoming particle was accelerated before it struck, so there must be something else at work here. I wonder if it's the incoming particle shifting the whole mass in the negative direction as it pulls on the magnet, and if the magnet were fixed in place if just one ball would move off.

One of the things that I dislike the most about the Sift are the numerous times that words and intentions are put into my mouth that are utterly absent in what I actually say.

I have repeatedly said "unconscious" sexism. And I have applied that phrase to both men and women.

But suddenly I am being painted as some hysteric who is lashing out at the big bad men who have hurt me so bad by their big bad sexism.

This entire culture is sexist. Anyone who has spent more than five minutes looking around them will agree with that statement.

If that feels like an assault to you, rather than a statement of fact, I would ask you to look inside and ask yourself why you are so defensive about a statement of fact.

I'll repeat what I said before -- do you really think you know absolutely everything about everything and have nothing to learn? Spend one day -- one day -- listening to how often women are called girls. Substitute the word "woman" if she is more than 18 years old, and see how that shifts your internal landscape. Spend one day -- one day -- substituting the word "boy" every time you hear the word "man" and see if it doesn't squeege you out.

You can call this trolling if you want to. I call it my little attempt at education.

I also know that it is pretty fruitless. Like I said before, I first started having this conversation FORTY YEARS AGO, and after some headway in early days, it is now worse than ever.

I am grateful for the strides women have made in the past sixty years. I am aware that, although there may be cultures where women have been heads of state (India, Pakistan) where America can't quite bring herself to do it -- still and all, American women have many more rights than those other cultures.

I am grateful that young women today are so blase about their own sense of equality that they blithely minimize themselves with their language. They don't know what it was like forty years ago -- there were authors and authoresses when I was growing up. Poets and Poetesses. Now there are authors and poets. That is so cool, I can't hardly stand it.


>> ^xxovercastxx:

Context matters.
Calling a grown woman "girl" at the workplace is probably out of line. Calling a few racist, drunk hipsters "girls" seems rather appropriate. If you are immature enough to shout racist remarks at strangers, you are immature enough to be justifiably called "girl". Is there such a thing as a mature hipster? I'm inclined to say no.
I voted for the video because I enjoyed it but your trolling makes me want to vote against. Worse still, you've made me agree with @Yogi.
As for knowing Sifters and their personalities, try this... As you read the responses attacking your statements, you're dismissing them as the opinions of sexist men (boys?), the products of a blatantly sexist world. You might also be thinking that if you've done or said anything wrong, it's because you're damaged from decades of sexism and thus your mistakes are our fault anyway.
How'd I do?

>> ^flechette:

Ok, so where's the footage of them hitting the metal with the beam? Dangit, we want EXPLOSIVE science!


You can be the first I am sure. Write a letter. You could BE explosive science !

Yes, because developing military systems that can reach any point on this planet in less than sixty minutes while carrying "more payload than just a camera" is the perfect answer to her question what should be your ultimate goal to work on if you knew you couldn't fail. What about world peace? ;-) I know, i'm some sort of hippie...

Nevertheless: One of the best TED talks i've seen so far and besides the military agenda a great motivator. Should be shown in schools to encourage young minds to keep an open mind towards engineering and science careers instead of just focusing on business and management positions.