Search found 172 matches

by rho
Tue Aug 23, 2011 1:01 pm UTC
Forum: Science
Topic: Wait, WHY don't heavier objects fall faster?
Replies: 76
Views: 14442

Re: Wait, WHY don't heavier objects fall faster?

Pop quiz. You have two identical spherical masses of uniform density in free space. They each have radius r and mass m. They begin with a distance x between their centers, where x > 2r, and at rest relative to each other. How long does it take for them to collide? You may use your choice of Newtoni...
by rho
Sat Dec 11, 2010 1:36 pm UTC
Forum: Computer Science
Topic: CUDA Vs Open CL for Colloidal Dispersion Simulation.
Replies: 12
Views: 4257

Re: CUDA Vs Open CL for Colloidal Dispersion Simulation.

Here's a long over-due update for anyone who's interested. It sounds like what you're doing is essentially an n-body simulation. Given N-bodies and some pairwise interaction, evolve the system forward in time. Since you're doing a Monte Carlo approach, you probably can get a nice speed up by running...
by rho
Mon Oct 04, 2010 7:30 pm UTC
Forum: Computer Science
Topic: CUDA Vs Open CL for Colloidal Dispersion Simulation.
Replies: 12
Views: 4257

Re: CUDA Vs Open CL for Colloidal Dispersion Simulation.

Firstly, let's hit the obvious. CUDA is Nvidia's CLOSED system while clearly OpenCL is not... Normally I'd pop for the Open system every time, but it happens to be that all the cards I have access to at the moment are NVidia ones and from what I've read CUDA is the more mature system with more supp...
by rho
Mon Oct 04, 2010 10:44 am UTC
Forum: Computer Science
Topic: CUDA Vs Open CL for Colloidal Dispersion Simulation.
Replies: 12
Views: 4257

CUDA Vs Open CL for Colloidal Dispersion Simulation.

So, I have a project this year involving the simulation of colloidal monolayers, simulating and identifying phase transitions between solid, hexatic and liquid phases. This involves simulating a large number of particles, for a long time, with a soft interaction potential between them. From what I'v...
by rho
Sun Oct 03, 2010 2:49 pm UTC
Forum: Science
Topic: Cause of radioactive decay
Replies: 8
Views: 2596

Re: Cause of radioactive decay

As GeorgeH mentioned, Bell's Theorem only rules out local hidden variable theories. Something like Bohm's hidden variable theory is still perfectly fine. Only if you're married to locality, among other things. " Although not quite being married to locality, we seem to be having having a very f...
by rho
Sun Oct 03, 2010 1:28 pm UTC
Forum: Serious Business
Topic: Do anthropogenic climate change deniers matter?
Replies: 58
Views: 9352

Re: Do anthropogenic climate change deniers matter?

Surely the fact that zookap has managed to entirely derail this thread, ignoring the science and instead refocussing on the obscure paranoia that Bill Gates is a eugenicist actively working to kill people with vaccines*, demonstrates the influence of climate change deniers? There is a well establish...
by rho
Sat Oct 02, 2010 3:52 pm UTC
Forum: Science
Topic: Cause of radioactive decay
Replies: 8
Views: 2596

Re: Cause of radioactive decay

Science can't prove that something doesn't have a cause. The cause could always be something that we just haven't observed yet. (assuming no hidden variable theory applies). Can do a bit better than assuming No Hidden Variables. See: Bell's Inequality. But yes, nuclear decay is probabilistic, ultim...
by rho
Sat Aug 14, 2010 3:40 am UTC
Forum: Science
Topic: An experiment in psychology.
Replies: 15
Views: 1917

Re: An experiment in psychology.

What determines "success" here? You need to decide what effect you expect your intervention to have, how to identify that effect if it exists and how to ensure that the cause of the effect really was the intervention. A hypothesis needs to be falsifiable. For example "The heart rate o...
by rho
Mon Aug 09, 2010 1:25 pm UTC
Forum: Science
Topic: physics questions
Replies: 5
Views: 898

Re: physics questions

Gravitational field strength increases at the surface of the star due to the decrease in radius, yes. Intuitively, if you imagine yourself on the surface of a small sphere, you are closer to every point of mass in that sphere than you would be on a larger sphere of the same mass, so using only Newto...
by rho
Fri Jun 18, 2010 5:58 pm UTC
Forum: Science
Topic: If x was different then how would y be different?
Replies: 19
Views: 1663

Re: If x was different then how would y be different?

Let the average life expectancy of a man be E years. Let the average number of hours walked per day be H hours. Let the average walking speed of a man be S miles per hour. Let the average road length be L miles. Then the average number of roads a man must walk down is clearly H*365*E*S/L. Letting E...
by rho
Fri Jun 18, 2010 5:18 pm UTC
Forum: Science
Topic: Cell phones asplode your brain with radiation???
Replies: 77
Views: 7034

Re: Cell phones asplode your brain with radiation???

Hmm. Could the headaches be from eye strain of using such a small device/screen? This would explain a connection between usage and symptoms, while agreeing that it's not from "Gee Willikers COSMIC RAYS THAT BURN!" As said, "if" there is any effect, it's likened to wearing a hat ...
by rho
Fri Jun 18, 2010 5:05 pm UTC
Forum: Science
Topic: Cell phones asplode your brain with radiation???
Replies: 77
Views: 7034

Re: Cell phones asplode your brain with radiation???

A cell phone can output up to 2W, depending on the country, most of which is NOT absorbed by your brain, otherwise you couldn't get a communication. This is only half true, in skin at 900 MHz the amplitude of the electric field falls to 1/e after about 4 cm. So the intensity drops by 1/e after 2 cm...
by rho
Fri Jun 18, 2010 4:47 pm UTC
Forum: Science
Topic: Cell phones asplode your brain with radiation???
Replies: 77
Views: 7034

Re: Cell phones asplode your brain with radiation???

From the research I read (a while ago now), as stated above the thermal effects are minuscule and the radiation is non-ionising so there's no clear mechanism for direct damage. There was an alternative explanation for some of the effects that people report (headaches, sleep loss, etc..), that the pu...
by rho
Mon Jun 07, 2010 5:49 pm UTC
Forum: Science
Topic: How small would it take for a thing to orbit a bowling ball?
Replies: 15
Views: 2239

Re: How small would it take for a thing to orbit a bowling b

badwiz wrote:In general, fast speeds mean larger smaller circular orbits.


Fixed.
by rho
Sun May 23, 2010 11:43 am UTC
Forum: Science
Topic: Temperature and velocity
Replies: 2
Views: 1216

Re: Temperature and velocity

Yeah, the average energy of an atom/molecule can be given classically by the equipartition theorem . Essentially, energy in an atom/molecule is stored equally, on average, between all of it's degrees of freedom of a molecule, where a degree of freedom is a quadratic term. You can work out how many d...
by rho
Sun May 16, 2010 12:07 pm UTC
Forum: Science
Topic: Science and programming
Replies: 13
Views: 1718

Re: Science and programming

Complex Systems.

There's also a lot of complex systems research at the Physics/Biology interface. Simulation is central.

e.g. CoMPLEX

There's a lot of bullshit out there too though, be wary.
by rho
Tue May 11, 2010 1:24 pm UTC
Forum: News & Articles
Topic: UK Election Results
Replies: 58
Views: 6673

Re: UK Election Results

1.) Labour: We have ended the age of boom and bust! (i.e., abrogated the laws of economics by the powers of positive thinking.) 2.) Labour and Conservative: Invading Iraq is a cunning plan. 3.) Lib Dem: I can't think of a better time to move closer to the Euro than right now. 4.) Conservative: Most...
by rho
Tue Apr 27, 2010 2:30 pm UTC
Forum: Science
Topic: So, quick question. (Earth stopped in its tracks)
Replies: 103
Views: 8100

Re: So, quick question. (Earth stopped in its tracks)

On a related note, what if the sun just disappeared? The earth would immediately be flung from its orbit, and no one on earth would know for 8 minutes, right? Huh... Just found this thread. Usefully, I was given an assignment recently to write a Solar System simulation program. It's an N-Body simul...
by rho
Sun Feb 21, 2010 8:31 pm UTC
Forum: Science
Topic: public misconceptions
Replies: 1073
Views: 140105

Re: public misconceptions

Okay, I just had someone ask me "if you dropped a pen on the moon would it have enough mass to fall to the ground". I also remember overhearing, on a train "yeah, you don't really feel it when it's going fast, only when it's going slowly." Thinking about it, we've all spent a pre...
by rho
Sun Feb 21, 2010 12:53 am UTC
Forum: Science
Topic: public misconceptions
Replies: 1073
Views: 140105

Re: public misconceptions

That travelling faster than light is just an engineering problem. "But we broke the sound barrier so..." And yes, it's amazing how many people don't believe there's gravity in space :? As we're sharing anecdotes: I was doing some image processing and my girlfriend turned up just as I'd got...
by rho
Mon Feb 01, 2010 1:27 am UTC
Forum: Science
Topic: Airzooka physics
Replies: 10
Views: 2659

Re: Airzooka physics

Well I'm actually more interested in the underlying dynamics AND I already have a real one, but just for fun I just made one out of a folger's coffee can and a latex condom roughly based upon your design(the reservoir tip replaces the string in your diagram). The results were less than stellar. I d...
by rho
Tue Jan 26, 2010 1:21 am UTC
Forum: Science
Topic: Modern einsteins
Replies: 92
Views: 9158

Re: Modern einsteins

How about Mitchell Feignbaum?

He fits the criteria of being alive and his work has led to an entirly new science and new ways of describing (quantitively) phenomena that were thought to be indescribable.
by rho
Tue Jan 26, 2010 12:42 am UTC
Forum: Science
Topic: A sliding and rolling cube
Replies: 20
Views: 2321

Re: A sliding and rolling cube

This would technically work, but it can't vary for different amounts of friction. It will roll at a 45 degree incline every time. Not true. If the coefficient of friction is less than 1, it will still slide even at very steep angles. You can confirm this with a d6 and a book. Right. that's what hap...
by rho
Mon Jan 25, 2010 3:31 pm UTC
Forum: Fictional Science
Topic: What is the mass of a feather?
Replies: 229
Views: 314995

Re: What is the mass of a feather?

ocdscale wrote:Shouldn't feathers have negative mass because birds float in the air?


Yeah, you're confusing feather mass with effective feather mass.
by rho
Mon Jan 25, 2010 3:18 pm UTC
Forum: Science
Topic: A sliding and rolling cube
Replies: 20
Views: 2321

Re: A sliding and rolling cube

Easiest way to think about it is to draw a vector from the CoG in the direction of g. If the vector passes through the base* of the cube, nothing will happen, if it passes outside the base, then it will roll. (Assuming a rough surface). Same result applies for an arbitrary shape, and in more dimensi...
by rho
Mon Jan 25, 2010 2:54 pm UTC
Forum: Science
Topic: They actually teach this bollocks in GCSE chemistry!
Replies: 68
Views: 8522

Re: They actually teach this bollocks in GCSE chemistry!

I think the problem ultimately lies outside the Chemistry and Physics specifications entirely. The problem is maths. Have you seen this shit they stick in the course guides? http://1.bp.blogspot.com/_I-O13W_ItLI/SsKQVDYo04I/AAAAAAAAAEI/kz1kS3FuUR0/s400/EquationTriangleSpeed.jpg The put this in becau...
by rho
Fri Sep 11, 2009 8:56 am UTC
Forum: Science
Topic: "Visible" Light
Replies: 9
Views: 1106

Re: "Visible" Light

This reminds me of a question Richard Feynman was once asked (recited from memory, so take with a pinch of salt): Questioner: Do I really see an apple or do I merely see the light from it? Feynman: This sounds like one of those rather dubious philosophical questions... Yes, you only see the light fr...
by rho
Sat Aug 29, 2009 3:17 pm UTC
Forum: Science
Topic: Physics and Dreams
Replies: 18
Views: 1930

Re: Physics and Dreams

My dreams are often irritatingly realistic. While attempting to lucid dream I was told that an excellent way of realising you're asleep is to become obsessed during the day time with checking whether you're awake or dreaming by performing a simple physical test - e.g. jumping and trying not to come ...
by rho
Sat Aug 29, 2009 2:50 pm UTC
Forum: Science
Topic: The problem with vactrains
Replies: 81
Views: 8801

Re: The problem with vactrains

Sure you can. You just need a frictionless tunnel going there. The beauty is that the trip would take some 40 minutes no matter how far you go. A frictionless straight tunnel through the centre of the Earth... It would take 40 mins if I wanted to go from the UK to Australia(ish), but If I wanted to...
by rho
Sun Aug 23, 2009 2:21 pm UTC
Forum: Mathematics
Topic: So where have I been?
Replies: 6
Views: 876

Re: So where have I been?

It's really not so bad. Such functions exist and are constructable as long you're not really anal about the specifics. You can just construct functions for body A_n's position relative to body A_n+1, and add them as far as you want to go. If, say, you're interested in your position within the solar...
by rho
Fri Aug 21, 2009 10:47 pm UTC
Forum: Mathematics
Topic: Pseudorandom Number Generator
Replies: 10
Views: 2013

Re: Pseudorandom Number Generator

Semi-related: I always thought this was a neat solution.
by rho
Fri Aug 21, 2009 10:12 pm UTC
Forum: Science
Topic: [PHYSICS] [CHEMISTRY] ideal and semiconductor diode
Replies: 2
Views: 787

Re: [PHYSICS] [CHEMISTRY] ideal and semiconductor diode

A general junction diode characteristic can be found here: http://hyperphysics.phy-astr.gsu.edu/Hbase/solids/diod.html#c3 An Ideal diode would allow zero current for all reverse bias and infinite current for all forward bias. For reference, A general zener diode characteristic: http://hyperphysics.p...
by rho
Fri Aug 21, 2009 9:43 pm UTC
Forum: Science
Topic: Metabolizing copious amounts of alcohol
Replies: 9
Views: 1392

Re: Metabolizing copious amounts of alcohol

Repeat exposure will also increase the levels of enzymes in th liver that break down alcohol. So you'd expect to be less drunk/drunk for a shorter amount of time if you'd had a lot to drink in the preceding weeks.
by rho
Tue Jul 21, 2009 3:26 pm UTC
Forum: Science
Topic: Physics ib e.e
Replies: 7
Views: 1126

Re: Physics ib e.e

To save energy on a fridge, make the heat pump in it more efficient, insulate the box better and and put a better heat sink on the back. There is no other way. If there is a temperature gradient because of the heat dumped in the back, then removing the gradient will give you more than trying to use...
by rho
Tue Jul 21, 2009 2:42 pm UTC
Forum: Science
Topic: EM wave question
Replies: 1
Views: 435

Re: EM wave question

Yes, It depends on the band structure of the molecule which can be found by finding the wavefunctions for the molecule. See Linear Combination of Atomic Orbitals (LCAO method) . Or, If your molecule forms a solid crystal lattice, Bloch waves . Unfortunately it's all quite involved QM so trying to le...
by rho
Mon Jul 20, 2009 4:12 pm UTC
Forum: Mathematics
Topic: chaos grapher
Replies: 9
Views: 1625

Re: chaos grapher

Try XaoS.

"From version 3.3 you can create your own formulas as well."
by rho
Mon Jul 20, 2009 3:47 pm UTC
Forum: Science
Topic: Impossible physics problem
Replies: 12
Views: 1498

Re: Impossible physics problem

The question should really have asked for the acceleration between 5 and 10 seconds. And stated that the lift was at rest for the first 5 seconds (or moving at a constant velocity) - But then who starts a question with a constant velocity, eh?
by rho
Mon Jul 20, 2009 3:16 pm UTC
Forum: Science
Topic: Physics ib e.e
Replies: 7
Views: 1126

Re: Physics ib e.e

I think the answer is no, actually. Given that to generate electricity from waste heat you'd be looking to exploit a temperature differential. See Thermocouple . Where as PV Cells operate via the photo-electric effect. It's possible you could get some current from a PV-cell working in the infra-red,...
by rho
Fri Jul 17, 2009 12:33 am UTC
Forum: Science
Topic: Psuedoscience
Replies: 9
Views: 1444

Re: Pseudoscience

Hollow Earth theories are quite fun. Basically the earth is hollow and has a mini sun at it's centre. There are entrances at the poles and there's a super-advanced civilisation living on the inside (despite gravity) but there's a big cover up so no one knows... ... If you read far enough there are U...
by rho
Tue Jul 14, 2009 11:07 pm UTC
Forum: Science
Topic: Escape velocity
Replies: 14
Views: 1766

Re: Escape velocity

nbonaparte1 wrote:On a similar note, does a black hole have an escape velocity of C?


At the event horizon.

You can actually calculate the Schwarzschild radius by starting with an escape velocity of c and working backwards using only classical mechanics.

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