## Search found 709 matches

Thu May 06, 2010 7:27 pm UTC
Forum: Science
Topic: public misconceptions
Replies: 1073
Views: 149963

### Re: public misconceptions

Ok, I have not googled it yet, but what's the difference between a sound wave and a shock wave? (Oh, does a shock wave travel faster than sound?) I saw a slow mo video of a bomb explosion. Watching the shock wave propagate across the field was amazing. Only amplitude. The speed of sound in a substa...
Sun May 02, 2010 7:06 pm UTC
Forum: Science
Topic: Thermodynamics problem
Replies: 2
Views: 2030

### Re: Thermodynamics problem

The change in entropy of bodies 2 and 3 when coming into thermal equilibrium will be \Delta S = \int_{T_{3i}}^{T_{2f}} \frac{C dT}{T} + \int_{T_{2i}}^{T_{2f}} \frac{C dT}{T} = C \ln \frac{T_{2f}^2}{T_{3i}T_{2i}} The change in entropy of body 1 must be equal to the combined entropy change in bodies ...
Sun Apr 25, 2010 2:03 am UTC
Forum: Science
Topic: Looking for a WAV Editor for Acoustics Research
Replies: 4
Views: 910

### Re: Looking for a WAV Editor for Acoustics Research

Thanks, Dream. I'll look into those.
Fri Apr 23, 2010 4:00 pm UTC
Forum: Science
Topic: Looking for a WAV Editor for Acoustics Research
Replies: 4
Views: 910

### Re: Looking for a WAV Editor for Acoustics Research

Thanks SWGLassPit. The problem with audacity is that it can't write wav files with more than 2 channels.
Fri Apr 23, 2010 2:28 pm UTC
Forum: Science
Topic: Looking for a WAV Editor for Acoustics Research
Replies: 4
Views: 910

### Looking for a WAV Editor for Acoustics Research

I'm looking for a WAV editor for use at my co-op job to analyze recording of UAVs. Ideal features: -Free -Easy-to-Use FFT -Ability to Read\Write WAV Files with Multiple Channels of Audio (More than two) -Cross-correlation functions I appreciate any suggestions, even if they don't have all of these f...
Mon Apr 19, 2010 5:38 pm UTC
Forum: Science
Topic: EMP and Engines
Replies: 3
Views: 762

### Re: EMP and Engines

According to this report, most modern cars will survive an EMP with no problems or only minor problems, due to their shielding against electromagnetic interference. I would imagine that even a General Aviation engine would have more shielding than a car, and would therefore be even more survivable.
Wed Apr 14, 2010 9:58 pm UTC
Forum: Science
Topic: About the speed of light
Replies: 17
Views: 1974

### Re: About the speed of light

Vaporice wrote:But according to you all, what would happen would be that the pole would first be compressed, and later it would be expand again on the top of the pole? And this at the speed of sound?

This is exactly correct.
Tue Apr 13, 2010 6:14 am UTC
Forum: Science
Topic: Speed of Sound Humidity Dependent Formula
Replies: 1
Views: 643

### Re: Speed of Sound Humidity Dependent Formula

Try "The variation of the specific heat ratio and the speed of in air with temperature, pressure, humidity, and CO2 concentration," Owen Cramer, The Journal of the Acoustical Society of America, 1993, p.2510.
Fri Apr 09, 2010 8:39 pm UTC
Forum: Science
Topic: Need help with a physics problem
Replies: 11
Views: 1631

### Re: Need help with a physics problem

To make sure the units agreed in the equation, I multiplied 7.8 and 4 by 3600. Here's your problem. Don't just multiply things by whatever feels right. You need to figure it out with actual thought. For instance, 1 revolution/hour needs to be multiplied by something that has hours on the top and se...
Sun Apr 04, 2010 9:17 pm UTC
Forum: Science
Topic: Liquids lighter than water and Water Rockets
Replies: 8
Views: 4099

### Re: Liquids lighter than water and Water Rockets

The mathematical model of a bottle rocket is, ironically, more complex than a chemical rocket, so the math and physics don't boil down to a convenient little equation like this . However, numerical methods work well for giving the delta-V of specific rockets. Playing around with the various constant...
Mon Mar 29, 2010 3:26 pm UTC
Forum: Science
Topic: Sources of Inspiration
Replies: 23
Views: 1994

### Re: Sources of Inspiration

nehpest wrote:Deep dark secret: the movie Down Periscope is what tipped the scales in favor of engineering over pure science.

Care to explain this? I'm an engineer and I like the movie, but I can't think of a link between the two.
Sun Mar 28, 2010 6:17 pm UTC
Forum: School
Topic: Movies Featuring people with mental problems
Replies: 16
Views: 2448

### Re: Movies Featuring people with mental problems

Batman. That guy has issues.
Thu Mar 25, 2010 9:13 pm UTC
Forum: Science
Topic: Integrating Distance vs. Time
Replies: 7
Views: 3227

### Re: Integrating Distance vs. Time

hawkmp4 wrote:Divide the integral from some time a to some time b of distance wrt time by the length of time b-a, though, and you'll have something possibly useful.

Average position.
Sat Mar 20, 2010 6:06 am UTC
Forum: Science
Topic: Is a pack consciousness possible?
Replies: 50
Views: 4567

### Re: Is a pack consciousness possible?

evilspoons wrote:What if another animal, constantly hunted by these pack creatures, evolved the ability to scream at precisely the pitch required to jam the pack ability?

Worse, imagine one of the pack members manipulating the rest to further its own reproductive success? An intraspecies predator?
Thu Mar 04, 2010 1:38 am UTC
Forum: Science
Topic: Arguing for the existence of chloroplasts
Replies: 22
Views: 2370

### Re: Arguing for the existence of chloroplasts

Well, there are plenty of phototrophic prokaryotes that get by just fine with no chloroplasts, so in a way he was right, but not really, because eliminating chloroplasts wouldn't eliminate autotrophs. If you actually eliminated all photosynthesis, then life would pretty much go to shit, though. Org...
Mon Mar 01, 2010 10:00 pm UTC
Forum: Science
Topic: public misconceptions
Replies: 1073
Views: 149963

### Re: public misconceptions

Would you, if the floor of the ship were sufficiently more dense than the walls and ceiling? You fall towards the center of mass of the vessel. However, this effect is negligibly weak. If you weigh 100 kg, and you're 10 meters away from a 100 metric ton mass center, the gravitational force is of or...
Fri Feb 26, 2010 3:16 am UTC
Forum: Science
Topic: Capacitor Charging Circuits
Replies: 3
Views: 1011

### Re: Capacitor Charging Circuits

Correct. Make sure you don't apply more voltage than the cap is rated for.
Fri Feb 26, 2010 3:13 am UTC
Forum: Science
Topic: Funding from the military
Replies: 60
Views: 5179

### Re: Funding from the military

Wed Feb 24, 2010 4:16 am UTC
Forum: Science
Topic: Chemistry-thermodynamics of reactions
Replies: 12
Views: 981

### Re: Chemistry-thermodynamics of reactions

Yeah, you could think of it that way: it's kJ per mole of (2 H2O molecules) or kJ per mole of (1 CO2 molecule and two H2O molecules)
Wed Feb 24, 2010 3:37 am UTC
Forum: Science
Topic: Chemistry-thermodynamics of reactions
Replies: 12
Views: 981

### Re: Chemistry-thermodynamics of reactions

I'm not sure what exactly you mean by this.
Wed Feb 24, 2010 3:18 am UTC
Forum: Science
Topic: Chemistry-thermodynamics of reactions
Replies: 12
Views: 981

### Re: Chemistry-thermodynamics of reactions

Stop thinking about it in terms of heat per mole of water. That's not what delta-H is. delta-H is not a property of the reaction. It's a property of a particular chemical equation with certain coefficients. It's tempting to think of it as heat divided by moles of product, but that's not what delta-H...
Wed Feb 24, 2010 2:40 am UTC
Forum: Science
Topic: Chemistry-thermodynamics of reactions
Replies: 12
Views: 981

### Re: Chemistry-thermodynamics of reactions

Think of it this way: multiplying all of the terms in that chemical equation by one mole gives you: 2 moles of H 2 + 1 mole of O 2 -> 2 moles H 2 O, with a delta-H of -572kJ. If you divided that equation by two, you would get 1 mole of H 2 + .5 moles of O 2 -> 1 mole H 2 O, with a delta-H of -572kJ/...
Fri Feb 19, 2010 6:56 pm UTC
Forum: Science
Topic: Stress Tensors and the static behaviour of Solids
Replies: 15
Views: 1689

### Re: Stress Tensors and the static behaviour of Solids

As a plate-like structure instead of a truss, do you reckon it's going to be stronger? You mentioned the Eiffel Tower earlier. Do you think there's a reason Mr. Eiffel made it out of beams rather than panels? I'm not saying your goal is impossible with panels, just that it's probably not the most p...
Fri Feb 19, 2010 5:44 pm UTC
Forum: Science
Topic: Stress Tensors and the static behaviour of Solids
Replies: 15
Views: 1689

### Re: Stress Tensors and the static behaviour of Solids

The equations I linked to only apply to plates that are loaded normal to the surface of the plate. That is not the case here. The way you are loading the plates in the drawing, you will have to worry about buckling, as Zamfir warned. I doubt you'll find any analytical solutions to the situation you'...
Thu Feb 18, 2010 6:47 pm UTC
Forum: Science
Topic: Stress Tensors and the static behaviour of Solids
Replies: 15
Views: 1689

### Re: Stress Tensors and the static behaviour of Solids

My impression is that the sphere is being supported by the faces of the plates, rather than on the edges, where buckling would be a factor. Regardless, the OP isn't designing a satellite for actual use; he is designing it for a class which, apparently, doesn't include structures as part of the curri...
Thu Feb 18, 2010 6:08 pm UTC
Forum: Science
Topic: Stress Tensors and the static behaviour of Solids
Replies: 15
Views: 1689

### Re: Stress Tensors and the static behaviour of Solids

I'd steer away from FEA unless you're only using it for very very basic analysis From the sound of it, that seems to be exactly what he's doing here. If I were he, I would model the geometry (pretty simple, judging by his description), then set up simple constraints (e.g. these 8 points are fixed b...
Thu Feb 18, 2010 1:18 am UTC
Forum: Science
Topic: Stress Tensors and the static behaviour of Solids
Replies: 15
Views: 1689

### Re: Stress Tensors and the static behaviour of Solids

Well, I got one of those and it goes into beams a lot but not much on plates. I essentially have a cuboid satallite, with a four-sided pyramid on the bottom with a spherical fuel tank suspended in the middle. Suspended how? There are some analytical solutions for flat plate deflection, mostly for r...
Thu Feb 11, 2010 11:36 pm UTC
Forum: Science
Topic: Flux
Replies: 18
Views: 1406

### Re: Flux

Basically, he's saying that the flux through a certain area (dA) is equal to that area times the field going through it (E dA) This only holds if the electric field is perpendicular to the surface. If it's not, you have to take that into account. It's still not very difficult, though, so I don't kn...
Fri Jan 29, 2010 9:42 pm UTC
Forum: Science
Topic: Thrust generated by pressurized air
Replies: 13
Views: 4861

### Re: Thrust generated by pressurized air

Okay, by the sound of it, you're talking about a fairly low-velocity airstream (less than a couple hundred mph), right ? If that's the case, then you can assume incompressible flow and just use Bernoulli's equation.
Fri Jan 29, 2010 2:48 am UTC
Forum: Science
Topic: Thrust generated by pressurized air
Replies: 13
Views: 4861

### Re: Thrust generated by pressurized air

This is the equation you want: http://en.wikipedia.org/wiki/Rocket_engine#Net_thrust. Note that Pe and Ve both depend on the geometry of the nozzle and you need a good bit of bit of college-level thermodynamics to figure out what they'll be.
Fri Jan 08, 2010 8:52 pm UTC
Forum: Science
Topic: Physics motion question
Replies: 6
Views: 1261

### Re: Physics motion question

Secateurs wrote:I then found the distance the second camel travels while accelerating (11.69512 m)

Check this.
Wed Jan 06, 2010 7:50 am UTC
Forum: Science
Topic: why would a photon drive suck so bad ?
Replies: 29
Views: 5826

### Re: why would a photon drive suck so bad ?

Carnildo has a good point- there is always a trade-off between mass required and energy required. Electric rockets are a way to sacrifice the kind of "efficiency" I discussed in favor of using less mass. These vehicles can afford to sacrifice energy-efficiency because their solar panels ar...
Wed Jan 06, 2010 3:52 am UTC
Forum: Science
Topic: why would a photon drive suck so bad ?
Replies: 29
Views: 5826

### Re: why would a photon drive suck so bad ?

The purpose of a drive is to change the momentum of the vehicle, while the cost of operating the drive is the energy of the propellant stream. Therefore, one measure we can make of the "goodness" of a drive is the amount of momentum change you get divided by the energy it costs you. Let's ...
Mon Jan 04, 2010 12:40 am UTC
Forum: Science
Topic: Heat and Ideal Gases
Replies: 10
Views: 1250

### Re: Heat and Ideal Gases

I want to heat from 0 C to 140 C, keeping it at a constant temperature How does this work? Perhaps it was a mistype and they meant constant pressure instead. Well, theoretically, molar specific heat at constant pressure is 5/2 * R for a monoatomic gas, so the answer in that case is 3 moles * (5/2) ...
Sun Jan 03, 2010 8:50 am UTC
Forum: Science
Topic: Heat and Ideal Gases
Replies: 10
Views: 1250

### Re: Heat and Ideal Gases

So let's say I have a certain amount of a monatomic ideal gas (three moles, to be exact) which I want to heat from 0 C to 140 C, keeping it at a constant temperature. How much energy (in joules) would I need to use to produce such a temeperature change? More importantly, is it even possible to calc...
Sun Jan 03, 2010 4:34 am UTC
Forum: Science
Topic: Heat and Ideal Gases
Replies: 10
Views: 1250

### Re: Heat and Ideal Gases

Ethliel wrote:I want to heat from 0 C to 140 C, keeping it at a constant temperature

How does this work?
Sat Jan 02, 2010 5:20 am UTC
Forum: Science
Topic: Optimal Rocket Trajectory
Replies: 6
Views: 1007

### Re: Optimal Rocket Trajectory

design the whole vehicle for the highest maximum value of C L 1/2 /C D where C L is lift coefficient and C D is drag coefficient. ESPLAIN! The range equation for rockets and jet engines and any other method of propulsion where thrust is proportional to fuel consumption is http://upload.wikimedia.or...
Sat Jan 02, 2010 4:33 am UTC
Forum: Science
Topic: Optimal Rocket Trajectory
Replies: 6
Views: 1007

### Re: Optimal Rocket Trajectory

I'll get the smart-ass answer (smart ass-answer?) out of the way: accelerate to orbital velocity, then let the rocket cover as much horizontal distance as you want it to, and de-orbit it. This requires a delta-V of twice orbital velocity, though. For a flat earth and realistic aerodynamics, you'd wa...
Thu Dec 31, 2009 8:09 pm UTC
Forum: Science
Topic: Aperture Science Hand-held Portal Device Related Physic Quiz
Replies: 19
Views: 2968

### Re: Aperture Science Hand-held Portal Device Related Physic Quiz

7. You have a sealed box containing two portals (each on one of the six interior faces) and a lit lightbulb. Figure out which sides of the box the two portals are on. You can't open the box. Measure the temperature of each wall. The coolest walls are the ones with portals on them, because the porta...
Thu Dec 31, 2009 11:57 am UTC
Forum: Science
Topic: Aperture Science Hand-held Portal Device Related Physic Quiz
Replies: 19
Views: 2968

### Re: Aperture Science Hand-held Portal Device Related Physic Quiz

8. You are a mad scientist. You note that Venus has too much atmosphere and Mars has too little for humans. You wish to fix this by shooting one portal at Venus and one at Mars. Assuming you can see both planets in the night's sky, in-transit portals travel at c, and a connected portal has cross-se...