Innit

I'm a total newbie at this topic, as I'm still doing my GCSEs (10th grade), but hasn't it been said that previously, 2 galaxies have collided, and together have joined to form 1 galaxy. From my knowledge, there are supermassive black holes (which are millions to billions times the mass of the sun) in the centre of galaxies, as there is one in the Milky Way. Somehow, I suppose, these black holes have joined to make one (NoteL This may be completely wrong, and I may have been misguided, because I also thought, as the above post states, that those two black holes were the closest apart!). One may have "consumed" the other, I am not sure. But if they are exactly the same size, maybe they would do orbit one another, like planets do. But I suppose that it would not be a normal circular motion. One would not be orbiting the other, they would be orbiting each other simultaneously. I have no idea what I'm talking about right now, but I think I'll stop there, before I confuse myself and others anymore!

If you look at the molecular level, rubber, for example, is sort of like a bunch of long molecular chains. When we bounce the ball, deformation at the bottom of the ball compresses these chains and places them into higher energy packing states. They quickly try to release this stored energy and return back to the lower energy state. The result is an expansion to release the stress that propels the ball back upwards.

 

Equal and opposite force applies so you can only get out what you put in. The ball also propagates some of its stress upward into the ball, with the result the ball will rarely bounce to the same height that it fell, unless you add some extra force to compensate for the impulse loss into the ball.

 

An interesting material is silly putty made from a silicone type rubber. This material will deform like putty in your hands, but if you throw it on the ground it will bounce like a solid ball. This has to do with the material only being able to deform with force impulses that are stretched out over time. If the impulse is too fast, it acts more like a solid material since the molecules are not able to slide past each other, storing local force.

 

For example, if you take some silly putty and stretch it slowly, it will stretch and elongate. But if you stretch it with a quick snap, it will shear off in a very smooth plane, as though one has sheared a solid material. The bounce force impulse acts the same way, with the compression too fast to allow the molecules to slide past each, causing a localized force build up, that will cause the putty material to bounce like it is a solid ball.

 

A kung fu master uses the force/time principle for breaking objects. The idea is to propagate a force impulse so fast that the material can not spread out the force and then bounce it back. The result is a fracture along a plane of the material. If you go too slow, the material will spread out the force and then bounce back the force into your hand, causing bone to fracture. The trick they use is to visualize the stopping point of your hand beyond the object. This assures that your hand won't slow down to soon especially at the point of possible force bounce back. There are demonstrations of some masters breaking a meter of ice. They know their physics, intuitively, and simply exploit a weakness in the material. It takes a lot of faith that science will work under these hazardous conditions.

That was brilliant! Thanks for that!

Triangles are the trick, I believe. They tend to keep everything more stable. That's why they're used in structures like bridges. You should try and form triangles, or as the others have stated "V's" or "W's" to keep the structure stable...

I can't really say much because I'm only 14, but from my knowledge, that is how it works...

I think you are confusing research on the persistence of vision and the current rate at which theatrical films are shown (movies are played back at 24 frames per second, the eye and brain do not necessarily perceive at this specific rate, nor is that the limit of perception).

 

Although retinal neurons can respond to flicker rates as high as 120Hz (120 flickers per second), the flicker fusion threshold across individuals varies quite a bit.

 

 

The eye is not a camera. It is a complex interplay of receptors, biological machinary, and aggregate firing patterns which are sent to various parts of the brain for processing.

Lol, I think I was confusing myself with the persistence of vision. Thanks for pointing that out, and sorry for explaining wrongly...

Innit---

 

Is this ``Inuit'' with an upside down `u'?

 

No matter.

 

Ask your questions and I will do my best to answer. You can also trust a guy named ajb (he knows MUCH more about the mathy side of things than I do). His avatar is a penguin (presumably because he likes Linux).

 

Anyway, perhaps we should start a general string thread? If this discussion goes long enough, perhaps we can get a moderator to do that (not Martin---I don't think he likes string theory very much).

 

Ok, extra dimensions.

 

The canonical example is a line strung between two poles. First some semantics---a dimension means that you can put a coordinate on it. The number of dimensions is the number of coordinates that you need to describe a surface. So, if you have a line strung between two poles, you only need one coordinate (i.e., distance from one end or the other). The top of your table needs two coordinates (`x' and `y' if you like), as does the surface of a sphere (think latitude and longitude).

 

Suppose that you're a tightrope walker, and you wish to walk across the tightrope. Well, you can describe your position with only one coordinate, right? You can use your distance from one of the end-points to describe your location. And as long as you tell me which endpoint you're starting from, and how far from that endpoint you are, I can find you.

 

Now suppose you're an ant living on that same string. If you're an ant, things look much bigger to you. If you are small enough, and the rope is sufficiently thick, you can see two dimensions now---you can see the distance along the rope, but you can also travel in circles laterally around the rope. In order for your ant friends to find you, you must give them two corrdinates---not only where along the rope you are, but also where around the rope you are.

 

The thing is, unless you are an ant, or unless you look sufficiently closely, you will NEVER notice that the rope has any more than one coordinate.

 

If this isn't clear, ask questions! Please!

 

Now extrapolate this out. Suppose we live in four dimensions. We know very well that we live in four dimensions, but we are big. Suppose we are very very small. Are four numbers enough to describe our position? The answer that strings gives is no.

 

Depending on HOW small you are, you either need 10 numbers or 11 numbers to describe your position. An easy way (and not completely inaccurate way) to think of this is to think of every point in space time as being described by four numbers (x,y,z,t), along with coordinates around 6 little circles. When I say little, I mean VERY little.

 

Again, because we are so big, we never notice the little circles---just like the tightrope walker may never notice the thickness of the rope, but the ant does.

 

I hope that this was a little clear. I haven't seen this video you have linked to, but hopefully my example was different from the video's example.

That was an excellent explanation! Thankyou very much for that. There are only 2 small things. First thing is that I don't quite understand is why exactly we cannot describe our position with 4 numbers. I didn't quite understand the concept of the "6 little circles", and what exactly they are.

The second thing is that, if I am not mistaken, I believe that we actually live in the 5th dimension, not the 4th. I think it was proved by Kaluza in 1919 and later approved of by Einstein. You'll obviously know better than I, but it was just what I'd heard...

Thanks

^ I see. Well, my knowledge isn't deep enough to have understood it so fully, but I guess I'll be awaiting BenTheMan's respones

I was always really confused about the concept of the 10 (and now some believe 11) dimensions. I came across this video that explains it in a simplified form (it's a video for the first chapter of a book):

http://youtube.com/watch?v=qU1fixMAObI

Pretty interesting. I got lost a few times, but I get it now!

It is said that your eyes view 24 "frames" each second. The reason that you're getting the impression that the wheels are going backwards is because every time your eye "captures a frame", one of the spokes of the wheel have been placed slightly behind the position of the spoke that was previously "further ahead" (the spoke you saw before is now probably half way down the wheel). This gives you the impression that the spoke has moved backwards. It's really hard to explain!

Whoops, just as I typed this I realized a link has been posted with the proper explanation. Oh well...

1. You remember what you've learned much better.

2. You can revise your notes - in your notes you would have probably taken down the key points, and can use that if you need to go through it quickly.

3. Sitting there and listening to a lecture without any notes is not going to help. It's like watching a TV episode, and trying to remember everything that happened 3 months later!

There are many more reasons, but those are the ones I can think of at the moment...