Physics

Something I never understood about the concept of time travel. Where are the previous states of the universe stored? The information must be preserved in order for the time traveler to immerse himself in that previous state of the universe. I've searched many threads here and haven't seen this addressed.

Ok I solved the last one past exam question by myself but this one has been bugging me for days, any help would be appreciated. A composit wall consists of three materials a, b and c, two of which are of known thermal conductivity ka=20W/mK and kc=50W/mK and known thickness La=0.3m and Lc=0.15m. The third material which is sandwiched inbetween a and c is of known thickness Lb=0.15m but unknown thermal conductivity, kb. Under steady state conditions, Ts,o(temp on surface of material c)=20°C and Ts,i(temp on surface of material a)=600°C. The temp inside T∞=800°C. The inside convection coefficient h=25W/m^2K a What is the value of kb b What are the temperat…

I just need some help with this past exam question. A counterflow concentric tube heat exchanger used for engine cooling in a very hot enviroment has been in servive for an extended period of time. The heat transfer surface area of the exchanger is 5m2 and the design value of the overall convection coefficient is 33W/m2k. During a test run, engine oil flowing at 0.1kg/s is cooloed from 110°C to 66°C by water supplied at a temperature of 25°C and a flow rate of 0.2kg/s. a. Calculate the operating convection coefficient b. If the ambient temperature is 50°C give a possible reason for the discrepancy

Runs on hot coffee or ice cubes!

If I have a blue and red LED (or theoretical light sources with pure blue and red light frequencies), and illuminate a white surface on the same spot, I seed pinkish purple light reflected. Is the reflected light of the same frequency as light from a light source with pure pink light frequency, or is the light a mixture of blue and red light. I believe it is a mixture, but I don't understand why a mixture of two lights could appear (to a human) the exactly same color as a completely different light frequency, in this case blue+red compared to pink. A related question; I have powerful LED light sources with blue and red light, which light up the entire room, and to my …

Hi Would anyone know if it is possible to induce vertigo in someone (inside a building) from a distance - say the length of 2 football fields - either with a device intended for something else or possibly a home made one?

The thermoelectric modules about 1/3rd down this page. http://www.unitednuclear.com/new.htm Roughly how cold does the chip get given how much power. For example a button cell, an 'aaa' cell, a powerful lithum battery about the size of a 'd' cell? Also could a resonable amount of power be created by placing one of thease in the temperature gradient between two materals of naturally different temperatures? I saw somone online doing something with a hollow materal full of a gas at a pressure to get the optimum of the materal being cold to the touch.

I wondered if this materal. http://www.mutr.co.uk/product_info.php?cPath=418_464&products_id=1151 Could be tightly coiled in a cointainer, then have heat such as (for simplicity) boiling water added into the container then the force to straighten the wire would be verry strong with potentally intresting applications.

Hypothetical question here. Lets say you have a peice of rope 1000 light years long, and you have someone on each end of the rope. the rope is pulled tight (so no slack). If one person pulls the rope, will the other person feel the pull instantly, or will it take time for the force to travel across the rope?

Greatings I am new? My question is east to stated but more difficult to answer (accurately) Assume we could remove the earth from any other heat source in the universe. Leave it somewhere in a hypothetical totally empty vacuum , except for itself of course How long would it take the earth, to dissipate all its heat by entropy, and freeze down to absolute zero, right down to its iron core Peace Alan

Energy equals Mass. Does that specifically excludes Mass without Energy. (like dark matter) Please and Thank You

Why can't vacuum permeability/permittivity be measured? I've read that they can't be measured .. is this simply because "pure vacuum" isn't attainable?

Hello everyone, I understand wavelength,frequency but not the amplitude. Can anyone here explain what do they mean by the amplitude. In some places they say it is the maximum displacement of a particle but isn't this the wavelength. My other confusion with sound is this Ok here the amplitude is the top bit from the graph. So it is maximum change in pressure. So why is it measured in m. Can anyone tell me what does this mean in particle level. If this is how sound spreads in all directions. I don't get it. Shouldn't sound follow a straight path like the longitudinal wave in the top picture. I thought sound was a longitudinal wave then why is travelli…

According to the Apple website the maximum operating altitude of the iShuffle is 3000 m (10,000 feet). Why should the altitude affect the operation of a solid state bit of electronics.

Not to say the universe is some giant ice cube always trying to melt away, but what all is matter. Basic definition has it as anything that occupies space and has mass, so does that exclude photons then? See I am trying to make some hypothetical assumptions about things, like if you can view physical processes as transformations involving stuff in the categories of matter and energy. Basic definitions of energy has that it’s the ability of a system to do work, or work done by a system in short, but the photon is just work then? I know it’s the confusion of dealing with words, but it’s the physics definition of matter that excludes photons from being in that catego…

I was just wondering: if there is a hypothetical pot enclosed on all sides such that steam from boiling water creates pressure at a certain temperature, then the temperature is increased, will the pressure increase in proportion to this temperature?

If we could dig a hole a 1 000 miles deep, what effect would it have on our weight,if we compared our weights from that measured on bathroom type scale. (bottom and surface)? I was a mining Engineer so this led me to propose this question (please overlook the ramifications of heat lava etc) Alan

This paper shows how http://arxiv.org/abs/0906.0809 It has pictures that make it easier to understand than if it was just equations.

Is it because of Newton's 3rd Law that you find it difficult to push a beachball under water? Thanks

Hello, this is my first post here, I'm not very passionate about physics, I'm a programmer but I have a little dilemma related to physics. I was talking with someone about nanotechnology and I said that we can create nanorobots in this way(theoretically): We create a "robot creator machine" that can also create a smaller version of it self. The smaller version of the "robot creator machine" will create a smaller version of itself and so on. We keep it up to a point we have a nanometric "robot creator machine". Then the robots the nanometric "robot creator machine" creates will also be nano. The person automatically refused the idea saying that this isn't poss…

Pondering on the question of j04hn on colour mixtures, I was wondering whether any of the harmonic relations that apply to sound actually also apply to light ? For example, a fifth chord (for example A 27.50 Hz --> E 41.20 Hz) sounds pleasant to the ear. Is there anything like a fifth chord for colours ? I looked at 450 nm and 675 nm (which have the same frequency ratio - 1.5 - corresponding to a fifth), deep blue and deep red, they look nice together (see http://www.pl.euhou.net/docupload/files/Excersises/WorldAroundUs/Spectroscope/Spectra/VisibleLightSpectrum2.jpg), but do they look any nicer than other combinations, I havn't had the patience to investigat…

Does long exposure to sound affects the struture intergrity of glass?

In an a document by him called "On Light and Other High Frequency Phenomena" i need help understanding this "If i am not precisley conscious of the motion, it is, because the images are vague or indistinct, being blurred by the superimposition of many. But when i perform the motion, does the impulse which prompts me to the action come from within or from without?" a few sentences later after describing the ideas of some people he explains what he thinks the answer is. This is where i got confused "I am convinced that the motive impulse must come from the outside. For, consider the lowest organism we know-and there probably many lower ones-an aggregation o…

In relation to an article i read in scientific america i was wondering if it is possible that galaxies are at strategic points in the universe whereby they are confined to certain regins which have a higher density that is condensing them into a particular formation thus creating an extreme pressure build up at the centre? eventually leading to black hole when the field collapses? instead of the theory that galaxies are revolving around blaack holes i beileve that galaxies are creating black holes when the surrounding space compresses to its maximum, and implodes upon itself?

Take a look at these pictures: In the first picture I have a light directly on that one square inch of paper, now if I move the light up, the square piece of paper will get less light...now if more pieces of paper are placed in the second pic to fill up the area of the light...would this equal the same amount of light as in the first pic under optimal conditions? Also, if I have a light bulb that emits light in all directions...if I add a reflector on top of that bulb to direct light to a certain point...how does that work with the inverse square law? Does the inverse square law only work with light emitting in ALL directions? What would change? …