Ask MetaFilter posts tagged with physics

To inifinity and beyond!

tomcochrane — Thu, 03 Jul 2008 06:13:21 -0800

What are some topics in astronomy or cosmology that you find fascinating and mind blowing? I recently took an introductory cosmology course at the university I attend, and have taken a couple astronomy courses before that. I've also been reading up on the topics a little, and I find everything fascinating.

Previously, I asked the hive mind about what math topics they thought were really cool. That thread brought about many very interesting answers. So now, with the upcoming 'switching on' of the Large Hadron Collider there must be lots of MeFites out there who find this as interesting as I do!

What blows your mind about astronomy or cosmology?

Let he who be without sine...

phrontist — Sat, 28 Jun 2008 19:00:54 -0800

Why are sine waves considered "pure" tones? Why do we consider sinusoids the building blocks of periodic functions? When analyzing physical, electronic, and acoustic/musical phenomena, it's often handy to view things in the frequency domain. I understand the basic idea of Fourier Analysis, namely breaking apart periodic functions in to the sums of sinusoids of given frequency and phase.

What I don't get is why or how sinusoids are "special". I know in the real world a great number of objects are essentially complicated dampened spring oscillators, so sinusoids are common in nature. Is that the end of it, or is there some deeper reason this function is good at representing periodic phenomena?

Isn't it possible to do a fourier analysis that breaks an arbitrary periodic function in to the sum of any other periodic function? Why not square waves, or a sawtooth?

While sine waves sound "pure" to me, it seems highly subjective. Is there something more than convention at work here? Some property of the ear?

The wikipedia page for sine waves reads...

The human ear can recognize single sine waves because sounds with such a waveform sound "clean" or "clear" to humans; some sounds that approximate a pure sine wave are whistling, a crystal glass set to vibrate by running a wet finger around its rim, and the sound made by a tuning fork.

This seems arbitrary though.

We say that the timbre of a violin is complex because it has many different harmonics. But the very idea of harmonic content assumes some basis function, right? Could we just as easily say a sine wave is complex by choosing square waves as our basis of spectral analysis?

So is this just a convention, and if so, where do we get it?

How do I fix a thermometer if the mercury has separated?

odinsdream — Fri, 27 Jun 2008 09:46:38 -0800

How do I fix a thermometer when the mercury has separated? I purchased a freezer thermometer. After getting it home the mercury (or whatever liquid they use in them now) had separated near the top of the scale, so there are bands of air between bands of red.

I tried heating it up, but this just compresses the band separation, then it returns to normal.

Instructions online say the fix is to get it cold enough that all of the liquid is pulled into the bulb. This thermometer goes to at least -35F on the readable scale, and a little past that before it reaches the bulb, probably -50F from the looks of it.

How can I fix it? Alternatively - do you work with liquid nitrogen and would you like to fix my thermometer?

Drill It Into My Head

kaizen — Sun, 22 Jun 2008 18:03:34 -0800

Help me understand electricity and physics and how they apply to motors. I have my head around electricity basics and electromagnetism, but I have a few unanswered questions about the more subtle aspects. Take a cordless / corded drill for example. When I press 'Go' on the drill, it is my understanding that a circuit is created, and in between sits the load / electromagnet(s). Is all of the electricity consumed by the electromagnet? If not, where does the rest go? Is the speed of the drill controlled mechanically through gears or through some type of electro-thingy? How does all that torque get created? Are there powerful magnets driving it? How is the motion reversed? Instead of asking a million questions, can someone explain how all the magic happens in a variable speed drill and where are those electrons eventually end up.

How do I teach myself General Physics over the summer?

Xere — Thu, 05 Jun 2008 23:29:52 -0800

After dropping out of Mechanics this spring, I'm starting General Physics in the fall. Which will hopefully be easier. I know from Mechanics that I'm terrible at physics, and I WILL fail unless I teach it to myself beforehand over the summer. I won't have any access to physics tutors or a summer physics class. How do I go about teaching myself? I'm majoring in Microbiology, and I had previously taken Mechanics with the engineering and physics majors because that was the only first physics class available this spring. I've finished a year of calculus, so the math wasn't a problem. I get the concepts. I just couldn't put all the pieces together to solve a given problem, and my highest exam score was 35/100, while some in the same class got 110/100!

I'd work the problems in my textbook, use a technique I thought was perfect ... and then I'd compare my answers and some other technique was used and thus a completely different answer. WHAT GIVES!?!?

This fall, I have General Physics available to me. In order to graduate on time, I absolutely have to finish this yearlong sequence without dropping out.

FWIW, the assigned textbook is College Physics by Raymond Serway. I have Young and Freedman's University Physics left over from Mechanics. I've been recommended this dvd set, though I've yet to buy it. Please let me know what else I can do.

Human (And Dog) Antenna

amyms — Sun, 25 May 2008 11:01:22 -0800

A question about how our bodies affect radio reception... We have a stereo in our living room that has poor radio reception. It is plugged into a power strip that is in turn plugged into a wall outlet (an inner wall, if that's important). It doesn't have an antenna.

Whenever one of us walks by, the reception gets crystal clear, and significantly louder. It reminds me of when I was a kid and we could get clearer reception on the television by holding the "rabbit ears" in our fingertips. But, with the stereo, there's no one touching any part of it when the phenomenon occurs. It even happens, though not every time, when our dogs walk by (they're both small terrier mixes, if that matters), but not when the cats walk by.

I understand that our bodies can act as antennae, but how does this work, especially when simply walking by the stereo without touching it?

Personally, I'd rather be a rock star...

shoebox — Sat, 17 May 2008 11:19:55 -0800

What can I do with a degree in Physics? What doors and pathways will it open for me? How long will I need to study before I am able to call my self a Physicist and make a meaningful contribution in my field? I'm about to make what seems to be the biggest decision of my life. Applications have been sent and responses have been received. Now comes the hard part.

My parents (one of whom is a computer engineer) are hell-bent on making me an Engineer (EE or CE) and have resorted to every known form of propaganda and coercion to force me to think like them. To be honest, I don't really think engineering is suited for me. I can certainly do the mathematics and tackle the theoretical aspects of it, but have never had the practical ability needed. I am horrendous when it comes to using my hands to do anything constructive (although I excel at things destructive).

The main argument my parents use is that engineering will quickly land me a good job after graduation, opportunities will be plenty money will come easy, whereas pursuing a career as a physicist would involve me studying till I get my Masters or PhD and most likely end me up in some teaching position (do not want) or spend the rest of my life as a lowly (and poor) researcher.

My question basically is this: Are my parents wrong when they say Physical Sciences is career suicide? Will I be able to do as well out in the "real world" following a career in Physics (Theoretical or otherwise)?

P.S. I will most likely attending U of Waterloo (physical sciences) or McMaster U (either physical sciences or engineering). Since engineering involves a common first year here, I have the choice when it comes to specialization so I definitely have more choices than my parents present me with.

Do you know what the symbols in this crypt mean?

lorbus — Fri, 09 May 2008 01:28:27 -0800

In the Cimitero Monumentale in Milan lies a crypt of the Galimberti family. Cuboid in shape, it bears numerous engravings which appear scientific in nature. I can make out what appears to be smashing particles, parabolas, lenses, and spirals. Is there a hidden meaning to all of this? A message? Code? Here are some photos: Full, Front, Door Detail, Left, Right, and Back.

If you need bigger images just let me know.
Thanks.

Wait a minute, stop the ride... I think I forgot to carry the 2...

SpacemanStix — Thu, 08 May 2008 15:53:39 -0800

So who's the person who gets to test a new roller coaster for the first time? I'm sure that the g-forces and physics of the ride have been worked out on paper and in computer simulations beforehand, and they've sent it through a few trial runs sans-humans. Still, I can't help but think that the first person to get on one of the newer fifty story coasters that are designed to make you wet your pants while plummeting a hundred miles per hour through a corkscrew is probably still wondering beforehand if all the numbers were worked out right. Who's the lucky person who gets to do this?

What is the g force experienced?

gummo — Mon, 05 May 2008 16:43:12 -0800

How would I calculate the G-Force of this impact? These are the things I know.

Start speed: 150 mph
End speed: 0 mph
Start position: 0 ft
End position: 8 ft

In other words, a car went from 150mph to 0mph in 8 feet.

What is the g force experienced?

Assume uniform deceleration.

Feynman made it too damn easy.

jmhodges — Fri, 02 May 2008 21:01:42 -0800

Quotation-filter. I'm trying to remember how a quotation went concerning Richard Feynman's lectures on physics. To paraphrase it: "You would be in his lectures believing you could do the physics, but when you went home, you realized you were not Feynman." Anyone have a clue?

I'm givin 'er all I got, Captain!

Saxon Kane — Mon, 21 Apr 2008 16:57:28 -0800

Where did the idea of faster than light (or near light speed) travel come from, and how is it described in different science fiction/fact works? I'm thinking partially in terms of the origin of faster than light or near light speed travel in scientific studies, but more specifically in terms of sci-fi. Many different sci-fi worlds, whether TV, film, prose, etc, have some form of travel that exceeds the limits of the speed of light. What are the various names of these forms of travel (hyperdrive, FTL, warp speed, etc), what are the technological requirements, affects, etc?

In terms of non-fiction, what are some of the challenges/possibilities discussed by scientists about near/faster than light travel?

How does physics impact poker?

jimmydare — Mon, 14 Apr 2008 21:44:59 -0800

Does the theory of the multiverse in contemporary physics mean that the top card in a deck of cards isn't "set" until it is seen? (ideal answerers have a background in physics, but all answers appreciated.) After a weekend in Atlantic City (I came out even, after expenses, so no harm done) I'm curious about whether the multiverse has philosophical implications in poker. Here's a situation. If I have pocket fives and (for various reasons too long to get into) I fold to a raise, and a five comes up on the flop: is it necessary that the same five would have come up if I had stayed in the hand? In other words, is the state of the flop "set" after the cards are shuffled? Or is it possible that had I stayed in the hand, the five would not have come up? This may seem a bit out there, but I feel that my future in cards hinges on the lessons of physics.

It's Slinky, it's Slinky, it's fun for a girl and a boy.

Blazecock Pileon — Thu, 27 Mar 2008 13:21:03 -0800

How fast would a typical escalator need to operate, in order to keep a standard metal Slinky moving indefinitely (i.e., in place)?

The more you know

Orange Pamplemousse — Mon, 24 Mar 2008 17:18:08 -0800

How has our understanding of Astronomy, Biology, Chemistry, etc. changed in the last five years? When I first started university I heard a lot of tales on how an education doesn't really instill 'facts', but instead improves a student's overall thinking ability. The key point in a lot of these lectures was that by the time I was five years past graduation most of what I had learned during my degree would be proven wrong, or at least incomplete.

So, fast forward a bit, and I'm wondering. How has our understanding of the world/ourselves really changed in the last five years?

What books or courses will help me learn science?

dylan20 — Mon, 24 Mar 2008 14:35:24 -0800

What books or online courses will best help me learn science and engineering? I'm especially interested in physics, astronomy, general electronics, and computer science. I've got what I think is a pretty good basic aptitude for science -- I did very well in it in high school -- but avoided taking science or engineering classes, or for that matter any math, through college. Now, 15 years after graduating, I feel that I may have missed my calling.

I'm interested in substantive introductory treatments of the topics -- not just "A Brief History of the Universe" glosses on the big picture, but books or courses that will help me understand what's really going on, from a basic level and building on up. Mind you, I'm not trying to turn myself into a physicist, I just want an understanding that goes beyond the vague fuzzy hand-waving stage.

I've started reteaching myself calculus using Silvanus P. Thompson's Calculus Made Easy, which is fun, and challenging. So I'm not afraid of math, as long as it's explained, or as long as I can figure out where to get an explanation.

Strings and String Theory

sleep_walker — Thu, 06 Mar 2008 06:33:33 -0800

I'm after violin sheet music that has been inspired by physics - any suggestions or recommendations? I've been reading about superstring theory lately, and was curious if anyone knew of composers who had/have written music inspired by aspects of physics.

I don't mind if it's not specifically for violin (though that would be great) as I am happy to adapt/transpose it. Having said that, I want to emphasise that I am just a dabbler, so my knowledge of contemporary/historical composers is very basic - my apologies if I've missed the obvious.

Big Bang Baffles Bonzai

Bonzai — Wed, 20 Feb 2008 23:55:07 -0800

Why is the Big Bang possible? I know that a black hole is formed when X amount of matter is in one place. I know that nothing (except Hawking radiation) can escape a black hole.

So if all the matter in the universe was once contained in a single point how could it have possibly escaped from all that gravity? Obviously it did, but ... how?

Math for pre-schoolers

billtron — Sat, 16 Feb 2008 07:42:11 -0800

My cousin's four year old son is obsessed with things like quarks and infinity. He insists to his mother that infinity is the last number. She isn't so sure, and wants to know more about things like strangeness. I don't want to determine this kid's future, but it seems fun to feed his curiosity. And since my wife's babysitter was Murray Gell-Mann, the responsibility has fallen partially on my shoulders to help answer his questions. What kinds of information can you recommend that I give to his mother so that she, an attorney and not a mathematician, and her son can learn more about this information. In particular, what kinds of books, games, and projects would introduce him to other neat ideas in mathematics and physics?

Crystal formation is an increase in entropy?

XMLicious — Wed, 06 Feb 2008 16:51:52 -0800

ScienceFilter: Creationists, crystals, and thermodynamics. A common red herring argument that I've encountered as advanced by Creationists is that by Newton's Second Law of Thermodynamics evolution should not be possible. (According to Wikipedia that argument was originated by a biochemist named Duane Gish, incidentally.) My understanding is that among other things, one reason why this is an erroneous argument is that while it might apply to a closed system the environment on Earth is constantly being pumped full of heat via sunlight and other solar radiation.

But never mind that, that's just the context. I was thinking about it and it occurred to me that in terms of orderliness increasing, the formation of ice crystals in freezing-temperature water or quartz crystals in liquid hot magma that has cooled to the correct temperature both seem to represent an increase in orderliness of the matter in question.

Something I've heard is that formation of crystals isn't strictly due to loss of heat. Supposedly you can have a quantity of water at a static temperature around freezing and if it's turbulent it will remain liquid but when it becomes still the ice crystals will begin to form. (Although hmm, maybe loss of turbulence would be a loss of heat.)

So is an ice crystal actually a higher entropy state than the equivalent amorphous mass of water?

Water expands when it freezes. I don't know why, van der Waals bonds or something, right? But other substances become more dense when they change state to a solid, so a given mass would lose volume. Isn't this kind of like all the air molecules in a room leaping into one corner of it - just the example that's presented as absurd in explanations of statistical mechanics?

I know that orderliness isn't the same thing as heat and isn't really the opposite of entropy. I was hoping that anyone who feels they've got a thorough understanding of thermodynamics could expound on what a thermodynamic analysis of the formation of crystals would be. And anything you can say about the relationship of order to entropy and thermodynamics would be interesting too.

In an eerie coincidence there was this recent post about the second law. The crystals must be telling me things.

Density? I'm dense.

beta male — Mon, 21 Jan 2008 20:28:34 -0800

Is there a chemical explanation for the density of an element or is it simply an innate physical characteristic? I can't seem to find an explanation of density that relates to something on the atomic level of an element. It doesn't seem to follow with an increase in atomic mass, number, radius, etc (Noble gases generally refute these possibilities). Is this something that is just inherent to each element?

Hopefully some of you are more hardcore science savvy than I am. Thanks in advanced.

Stop my tree swing from twisting!

zeoslap — Sat, 19 Jan 2008 17:13:54 -0800

How do you stop a tree swing from twisting? The branch it's attached to is higher on one side so the swing wants to twist. The swing itself it just a piece of wood with four eye hooks in it. How do I counteract the twist? Will some kind of stabilizer bar work? What is the best way to tie the rope (knot suggestions etc)

Thanks!

The mass of neutrons versus protons? The existence of matter?

bookish — Wed, 16 Jan 2008 17:33:47 -0800

Why do neutrons have more mass than protons? My fascinating, if frustrating, chemistry professor posed this question to the class. "Have you ever asked yourself that? You have to ask these questions. There is a reason for everything, and those reasons are important. The fact that neutrons have more mass than protons is vital to the very existence of matter."

But then he didn't explain, and I'm dying to know the answer, and why the answer is so significant. I've tried to figure it out on my own but so far, no luck.

How many electrons in each processor cycle?

Jimbob — Tue, 08 Jan 2008 05:04:01 -0800

In a modern CPU, how many individual electrons, approximately, are "let through" in each clock-cycle of, say, an individual transistor or logic gate? Are we close to managing the paths of individual electrons? Or are we still shuffling around millions of the little blighters in each transistor in each tick of a 2ghz processor?

More Cans = More Recycling = More Money. Make it so.

TomMelee — Wed, 02 Jan 2008 19:30:46 -0800

I see you there. You're smart. You've got great ideas. You want to help me make the world a better place. So, help me brainstorm this contraption. I work for a non profit. As part of our fund raising, we recycle cans. Lots of them. Hundreds and hundreds of pounds of them even. Trouble is, they don't usually come crushed. I can't afford a briquetter or a baler, so don't suggest that. We do have enough that a wall mounted single can crusher is probably not the best bet either. I thought about driving over them, I do have a double-wheel 3.5 ton truck, but I don't like that either since we're pretty public and have a gravel lot.

Last week we recycled 260lbs of cans, that was December's load. That's about to at least double in the next 2 months. Certainly not enough to warrant a bailer or briquetter.

So I'm thinking, what's the easiest way to crush these cans? My thoughts: I'd prefer a non-electric approach...or at least I don't want to plug it in. I wouldn't mind pneumatic, we do have a compressor (or we can get one).

Resources: plenty of PVC, sch 40 and 80, fittings, compressor, big truck, every power tool you can think of, wood of all sizes and dimensions, and just about any hardware you can think of. (hinges and screws to plugs and switches.) I could probably also spend another ~$200 if I needed to.

Requirements: Needs to be fast, ideally I dump a bunch of cans into a hopper and it starts crushing, or it crushes them all together. It needs to be safe and simple to operate, so that I can have volunteers and staff operate it often. Needs to be fairly small, or foldable, or suspendable. Lightweight would be ideal too, but I can deal with heavy. Also, it obviously needs to be able to deal with getting some soda/beer/whatever on it sometimes, and/or should be able to be hosed off, at least in the crushing area.

Bonuses: the tighter the crush the better. The more cans I can get in the same space the more money we make per cubic foot of storage space.

So mefites, get thinkin! Help me design my toy.