The moon. dammit.
I knew better butt was thinking about eclipses and told you some misinfo. It’s been 6 hours and it’s still bugging the crap outta me. I’m so sorry. dammit!
I’m not sure that this so much as a proper question as just an exclamation of disbelief…how in the hell can a relatively simple speaker reproduce complex sounds? Or is the mixture of guitar, drum, bass, and vocal that I’m hearing right now more of an aural illusion, being only one kind of sound that fools my ears into thinking that there are multiple sources of sound? For that matter, how can the grooves in a vinyl record reproduce complex sounds as well as they do? Sound is driving me cuckoo.
Dumbass science question alert
Maybe I missed the news article but I don’t get the whole gravity issue re not be able to see, find or specifically determine in some manner the medium by which gravity manifests itself. I’ve heard of theoretical particles called “gravitons” but IIRC these are are just a handy name for things that we think should exist. What’s the big hurdle? If we can smash atoms to their component bits and beyond why can’t we take apart or see the components of the medium by which gravity manifests itself.
Believe it or not, I was thinking the exact same thing, i.e., height vs time. Now that I re-read the question, it would seem that the question WAS asked for a thrown arc rather than straight up and down. Damn.
Okay, here we go:
- a) The moon has phases becasue as it orbits the Earth, different parts of it are lit by the Sun. Basically, we are watching the cycle of day and night on the Moon. The phase you see depends on where the Moon is with respect to the Sun on the sky; it’s full when opposite the Sun, new when near the Sun, etc. You can find out more here: http://www.badastronomy.com/bad/misc/moonphases.html
b) People all over the Earth see the Moon in essentially the same phase, because the Moon is far away compared to the size of the Earth. People in opposite hemispheres see it upside-down with respect to each other though. Constellations look upside-down too.
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The Moon showing the same face to us is not coincidence, but a natural outcome of gravity and tides. See here:
http://www.badastronomy.com/bad/misc/tides.html -
Eclipses: the Moon’s orbit is tilted by about 5 degrees to the orbit of the Earth around the Sun. The Moon and Sun are only a half degree across, so usually the Mon misses covering the Sun by quite a ways, which is why we don’t get solar eclipses very often.
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The ball’s velocity vertically is zero at the top of the arc, no matter what the horizontal velocity is. The vertical and horizontal velocities are completely independant. Here’s a question: you drop a bullet from one hand at the same time you fire one from a gun pointed horizontally at the same height. Which bullet hits the ground first? Neither. They hit at the same time, because they both fall at the same rate. The one shot from the gun will just hit the ground a long way away.
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Relativity: try here: http://math.ucr.edu/home/baez/physics/
Anything else? Bueller? Bueller? Bueller?
[phew! The BA goes off to rest his weary fingers…]
Cuckoorex - basically, you have multiple waveforms, which add up to create a complex waveform. This complex waveform could be drawn as an infinitely complex squiggly line, like a graph with time on the x-axis, and amplitude on the y-axis. All a speaker does is try to emulate that squiggly line by moving back and forth within its enclosure. The reason only one component can do that is because there is really only one waveform to deal with. Similarly, the needle on a turntable is riding on a groove that approximates that squiggly line. When it does, the vibrations are transformed into electrical energy, which is then decoded by the speaker.
There is a sort of aural illusion, but the brain can reach into a complex waveform and pick out individual instruments or noise sources, especially if the sources are dynamic. If the sources are static, i.e. playing a single note, the brain has more trouble decoding the info.
So a single speaker is all that is required to reproduce a complex waveform, but what really helps is the use of multiple speakers. When a group of musicians is recorded in stereo, subtle delay information gets encoded as part of the complex waveform. When played through stereo speakers, the info is decoded by the brain, and a stereo image, from which you can discern individual instrument locations, is formed. Hope this helps. And if I left anything out, everyone, please jump in and correct me.
Why does a ball with back spin tend to go up? I know it has to do with the Bernoulli principle, but it seems like the bottom of the ball is moving faster relative to the air than the top. That would mean the pressure on the bottom would be lower, and should force the ball down.
Old vinyl records are basically just a spiral groove that widens and narrows and the stylus/needle is just a small diamond running along in the groove.
How do you get from that to having the sounds of guitars, keyboards, drums, vocals etc?
[nitpick]
I’m not real learned 'bout stuff like this…but
I thought that I heard one time that
Ifyou were on a level field somewhere one earth and fired the bullets at the same time the one you drop would hit first because as the bullet you shoot travels away from you it has further to fall because of the curvature of the Earth.
Am I whacked out for thinking this?
I guess this is what I was talking about. I have the impression that I should be able to have an intuitive grasp of simple Newtonian things, without having to resort to churning through a bunch of equations and believing what the numbers tell me.
For example, a figure skater twirls faster when she pulls in her arms. Why? Because it follows from the conservation of angular momentum. But that’s not the real answer - each little piece of her arm doesn’t know about that, it just has inertia and goes where the forces pull it. Conservation of angular momentum is a non-intuitive shortcut that physicists have learned they can depend on. An intuitive explanation would say that as she pulls in her arms, they already have a high speed from making a wide circle, and that speed will be maintained (due to intertia) when she pulls them in a tighter circle.
So what is the intuitive explanation for how a gyroscope works (in particular, precession)? If I’m hoding the axle of a spinning wheel, and I apply a twisting force in the horizontal plane, why does the axle want to rotate in the vertical plane?
fired a bullet the same time as you dropped one
[/nitpick]
duhh…I think my brain is leaking out my ear…
[QUOTE]
*Originally posted by whatami *
**[nitpick]
Well, technically that’s true, but the curve of the earth is so small over the range of a bullet fired horizontally* that you won’t notice.
*that’s the trick. Gun sights are normally calibrated to fire upwards at a slight angle, so that the bullet doesn’t just fall straight into the ground, since it starts to drop as soon as it leaves the barrel, as described by the Bad Astronomer
I remember one of my science teachers explaining that the reason stubbing your toe was so painful was that the force exerted by your foot striking the stationary object was equal to the force created by dropping a piano on your toe. Does this sound even remotely correct to anyone? I could never make sense of the physics of toe-stubbing.
My secret shame really involves math…I could never master the greater than and less than signs 
Okay, I’ll take a shot at explaining how complex sounds are made by a single groove on a record. Although I’m mostly saying what syzygy said.
The single groove actually follows the pattern produced by the sum of two separate sources (say, a trumpet and a bass). Sound is produced by a movement of particles of air. Say you’re listening to a live performance. The bass starts playing some note, and the air pattern matches that note. Then the trumpet starts playing. Well, it’s the same air moving, so the movement of the air is going to be what happens when the sounds (air movements) add together. If you were to look at the air pattern, it’d be rather complex. But all you need to do to reproduce the sound is move the air in the same way. The groove on the record is thus the pattern that will make the speaker move the air in the same complex pattern.
I’ll attempt an analogy for how we hear separate sounds, but if it’s too confusing, don’t bother with it.
Suppose there are two identical lights flashing; call them B and G.
B flashes every 4 seconds, like this :
B _ _ _ B _ _ _ B _ _ _ B
G flashes every 3 seconds, like this :
G _ _ G _ _ G _ _ G _ _ G
So if both of those lights are flashing at once,
you'd get the following ( 'E' means both lights):
E _ _ G B _ G _ B G _ _ E
Now, imagine that you're far away from the lights, which
are close to each other, so you can't see two separate
light sources. All you see are flashes. Though when both
lights are flashing it looks twice as bright. What you see
is this (X is twice as bright as x) :
X _ _ x x _ x _ x x _ _ X
That ends up being a somewhat complex pattern.
But now suppose you have several detectors. These detectors have little windows that open every certain number of seconds. If they see a flash (no matter how bright), they mark an ‘X’ on a tape. If no flash, they mark _ . So, say you have a ‘B’ detector that opens its window every 4 seconds, a ‘G’ detector that opens its window every 3 seconds, and a ‘H’ detector that opens its window every 5 seconds. Here’s what each tape will look like after time:
B-detector (every 4 seconds):
X X X X
G-detector (every 3 seconds) :
X X X X X
H-detector (every 5 seconds) :
X _ _
Now, if you want to know what you saw, you look at the tapes. If a constant stream of X’s comes out, you know that that ‘tone’ is being played. But if you get any _'s, then you can say that that that ‘tone’ is not being played. So when you looked at the tape above, you know that both a B and a G, but not an H, were being played.
Up to now we were still talking about live light/sound sources. But if you could produce a light that flashes at various brightnesses with whatever pattern you choose, you can see you’d only need one light to make any number of ‘tones’ you wanted. This is analagous to the encoding on a record, or the sound made by a stereo.
This is pretty much how hearing works - and it shows how one apparently complex signal is summed to a single one but can be retrieved. Your ear acts like the detectors, and your brain “reads the tapes” to produce the sounds you hear.
One last clarification: It’s important to realize that in my analogy the B, G, and H represent single tones, not necessarily single instruments. When both the bass and the trumpet play the same tone, we can tell that both are playing because each instrument actually produces extra tones in addition to the main one. And in actuality, we wouldn’t recognize two distinct instruments unless we had previously heard both a trumpet and a bass separately (in other words, separating instruments is learned social information, separating tones could be considered an innate (or automatically learned) ability).
It never ceases to amaze me that teachers are willing to say outrageous things like this, that their poor students carry around as ‘facts’ for the rest of their lives. This is, of course, complete nonsense. For one thing, there is no universal force caused by stubbing your toe, because each incident is different. You can stub your toe with a hard kick, or by while slowly moving your foot.
Another difference between stubbing your toe and dropping something on it shouldn’t have to be explained, but apparently your teacher could use some remedial critical thinking skills - you drop a piano on the top of your toe, with the force going down through the top. You stub your toe on the front of it, with the force acting parallel to the direction of the ‘stubbing’.
BTW, if you drop a piano on your toe, it’ll do a lot more than just hurt for a few seconds. See you at the hospital.
My WAG as to why stubbing your toe hurts is because the fingers and toes have lots of nerve endings in them so that we can feel things more precisely, and because you’re putting a lot of force on a fairly small area. In terms of PSI, the pressure is significant. And I suspect that’s what your teacher was trying to get at. A better example of that would have been, “Why does it hurt so much when my dance partner steps on the top of my foot with her spiked heel, but it doesn’t hurt as much when she steps on my foot with the flat toe of her shoe?”
I think I’ve got this one dialed in. The reason the thing tilts in a direction perpendicular to what you’d expect is an artifact of circular motion, similar to the skater’s arms.
Imagine a large disk, not spinning, in front of you. The disk is oriented horizontally, so the axis of rotation (if it were rotating, which it’s not) would be vertical. You push up on the near side of the disk, it tips away from you. This makes sense.
You want to know why when it’s spinning it acts differently.
OK, imagine not a disk in front of you, but a single weight on a string attached to the top of a pole. The weight is spinning around the pole fast enough that its path forms a disk around the pole. The disk formed by the path is oriented exactly the same as the disk in the previous thought. As the weight passes in front of you, it is travelling to your right, meaning that if viewed from the above the weight is rotating counter-clockwise.
Now, at some moment in time, the weight is exactly in front of you and you smack it upward, imparting some force to the object for a split second. Where does it go? It doesn’t go straight up, because it was going to the right before. Instead, it continues going mostly to the right, but now it also goes up a bit. As it goes along its new path, it goes up and up as it is going to your right, but when it gets to 90 degrees from you it can no longer go higher because the string can’t get any longer. So, it starts down again, because it is now above the top of the pole. It crosses behind the pole at the same height it was when you smacked it and continues down until it reaches a low point on the left side of the circle, then comes back up to the point you smacked it.
The circle it traces out has not tilted away from you, but to the left! Yet, looking at a single weight, this makes sense. You can try this experiment with a tetherball like device (just avoid wrapping the rope around the pole, if you have a swivel it’d be perfect.)
How does this translate to a disk? Well, let’s return to our disk, and set it a spinning. If you push up on the near side of the disk, that portion of the disk is undergoing the exact same impulse that your single weight did. What about the bit on the opposite side? You are pushing it down! It therefore follows in the same tilted-to-the-left path. What about the bits on the left and right? You are not pushing on them at all, so they don’t care. But, because they are attached to the rest of the disk, they follow along.
Does that make any sense?
douglips, thank you for this explanation. I’ve visited websites in the past which attempt to explain gyroscopic precession intuitively, but I’ve failed to grasp it until you explained it.
Douglips I have had a good intuitive understanding of precession in terms of forces and accelerations for a long time (I’m a little bit of a math loony) but have never been able to put my understanding into words for anyone else to understand. You’re explanation is wonderfully intuitive and clear. There is, for just about any physical phenomenon, a nice, easily understood explanation. You’ve given that very thing here for us in regard to precession.
As the local Ask Mr. Question Man for family and friends I only have this to say to you: thankyou thankyou thankyou thankyou…
Nice work, Douglips
This is a wonderful thread. In my work as a professor of science education I have made an informal study of misconceptions which my students have reported to me. (There is, of course, a large body of fascinating research on misconceptions, etc.). There is an enormous amount of misunderstanding out there, and teachers of science are largely responsible for promoting it. I believe there are a number of reasons, not the least of which is the long-standing mythology that (science) teachers are supposed to know everything (about science). As a former science teacher, I know that expectation is large, sometimes overwhelmingly so, and I cringe to think of the times I’ve told a student something because I figured it was right. One of my favorite common misconceptions is this: we breathe in oxygen and breathe out carbon dioxide. If that were really true, why would we ever do mouth to mouth respiration? Of course, it has a semblance of truth and is actually an oversiplification. But people “learn” it in school and believe it forever in that form. I’ll keep reading, if you’ll keep writing. xo