Physics

I was just watching the Science Channel. The show was called "Cosmos," starring Carl Sagan, and he made a comment that at a gravity level of 1 million g, light continues to travel in a straight line, but a 1 billion g, light begins to bend towards the source of the gravity, as happens with a black hole. Correct me if I'm wrong, but I believe this would suggest that light actually has mass. I know that light is reffered to in the scientific community as a "wave-particle duality," but the particle part referres to a ball of energy, doesn't it? If light didn't have mass, then it shouldn't be affected by gravity. Am I thinking right?

Problem : Two blocks of masses 10 kg and 20 kg are connected by a string that passes over a pulley as shown in the figure. Neglecting friction between surfaces, find acceleration of the blocks and tension in the string (consider g=10m/s2 ). Solution : The blocks are connected by a taut string. Hence, their accelerations are same. Let us assume directions of accelerations as shown in the figure. Also, let the magnitude of accelerations be “a”. According to Newton's Law.F=ma ∑Fy=T−10g=10ay The problem is that. in above equation why we took T as positive and mg as negative? On the other hand in ∑Fy=20g−T=20ay i.e for "20Kg" we took T negative and mg positive. I w…

I have recieved some private messages from SFN members asking me about posting up some physics questions. Apparently my "Speed of Sound" thread went dry, so I'll try this one more time, and hopefully, people will participate. The first question is a high schooler question, but it will challenge high school students, and people without formal education alike. If you can answer the question, good job. I'll put up another question as it will get harder as it goes on. 1st question: A family has purchased a new 45-inch television and because they only own a subcompact car, they have placed it on the roof, as shown. Because they had no rope, the father used double-si…

Hi, I have a question regarding earthquakes. Does the rotation of the Earth have any effect on earthquakes? In any way.. I was thinking, Since the earth's crust are floating on magma, and not solidly 'attatched' the the core, if the angular velocity of one portion of the earth's crust is slower / faster than another portion, could that possibly cause shear i.e. an earthquake? Thanks

X Rays, UVLight, , Infer Red, Microwaves Take a sheet of paper and shine red light onto it, then shine green light onto the same place, the result is yello light. The elecromagnetic frequency for yello light is half way between red and green If instead you shine red and blue light you get purple, however green is half way in turms of frequency between red and blue, not purple. To me this makes little sence? This got me wondering weather someone could tell the difrence (for example) between light at the frequency for yello and equal amounts of red and green light (also making yello).

Do we know why gravity emits x amount of force from a y amount of mass? I know we can figure out how much gravity from mass, but do we know why x amount of weight delivers y amount of gravity from a z distance? Is there any situation where that can be different? how bout gas, can enough gas accumulate into an area to create gravity? Some people say we are all connected and some say nothing is connected and there are empty spaces between particles. So I'm assuming if we took trillions and trillions of humans and just put them close to each other that we'd combine our force and create a stronger gravity pull or...how does that work?

I am having my exam very soon and I have a question want to ask... it is that, friction between two bodies is determined by the equation, f=Nu, where f denotes the friction force; N for the normal force and; u for the friction coefficient, however, it is also known that the resulted kinetic friction force is proportional to the velocity of the sliding object. So does it mean that the velocity of the sliding object would affect the normal force? Or affect the friction coefficient? And I wonder the explanation for this phenomenon.

If GR already accounts for gravity, why do we need a theory of gravitons?

the final budgeting of ITER has been agreed upon and the construction of the complex is set to begin within the next couple years. Any thoughts?

I've had a look around and didn't find anything on this so thought I would ask. I need a simple formula that relates evaporation at a free surface to the air temperature at the free surface. I'm trying to model the effects of rainfall on landslip movement but need to adjust the rainfall values to include evaporation to see if the effect is significant. I have found many varying formulae online and in journals but they all include data that I just don't have. They require complex variables based on vegetation type for example and I don't need anything as accurate as that, what I need more is a crude relationship. The data I have is precipitation and air tempera…

Ok, I'm a little confused by Maxwell's paradox associated with light always traveling at light speed. Supposedly, Einstein pondered the state of affairs if we chased a beam of light at light speed, thereby causing the light beam to "appear" stationary. The question I have is, how is that a paradox? Just seems like common sense to me. We don't even need light to recreate the paradox. How about a car? If a car is traveling at 5 miles per hour, and I run 5 miles per hour along side it, then it will appear stationary relative to me. In both scenarios the car and the light are still traveling at their respective speeds, but I'm just running along with them. …

According to Greene, "the gravitational force allows us to declare that all observers - regardless of their state of motion - are on absolute equal footing. Even those whom we would normally think of as accelerating may claim to be at rest, since they can attribute the force they feel to their being immersed in a gravitational field." I can understand how we're all under the same force, so we're all in the same reference frame with respect to that force. But I don't see how that allows acceleration to be nulled. I thought that if I travel at 60 mph to work, while my buddy travels 40 mph on his way to work, that he has aged more than me - albeit in billionths of …

Ok, so I was just reading about Quantum Tunneling. About the energy a particle has can wildly fluctuate in a short enough time scale. This is somewhat difficult to absorb because it doesn't make any intuitive sense to me about "borrowing" energy and reqlinquishing it within a small timeframe. Where does it borrow this energy from? Other nearby particles? Greene explains that if you were to shoot a plastic pellet at a concrete wall, that the wave functions of the particles making up the pellet all have a tiny piece that spills out through the wall. And so, the pellet has a small chance of going through the wall after repeating the action enough times. …

It is generally agreed that Einstien should have won 3 nobel prizes instead of just the one that he did win. These would be for his paper published in 1905, on the photoelectric effect (that he did win one for), for special relativity and for brownian motion. This makes sense, considering how important these were. But what about General Relativity? I mean, even moreso than Special Relativity, this seems to fundamentally change the way we look at the universe. He did nothing less than replace newtons law of universal gravitation; one of the most important laws in physics. I would think that this, even moreso than his other would would earn a nobel prize. Yet it never s…

I have recently been studying the mathematics behind projectile motion through air resistance. We are given problems where the resistance force is proportional to v2 or v or something else (simple) containing v. I know that shape has alot to do with it but what is normally the function used for approximating air resistance for say, a spherical object. Or are such functions so complex that it would be impossible to solve without experimental data?

I've just started reading The Elegant Universe and I've run into the whole antiparticles thing again. What I don't understand and what never seems to be explained is: If every particle has a partner antiparticle upon which contact annihilates each other, then how can there be more matter than antimatter? Does something else also annihilate antimatter? I've run into this before, so apparently I'm missing something.

If a light particle went neer a black hole, then it would be pulled towards it, if it was close enough it would be pulled into the black hole. If not it would just be pulled off its otherwise straight path slightly. At some radius light must be able to orbit the black hole, we wouldn't see this light from a distance as it would be going round and round the black hole in the same way as a plant goes round and round a star. If anything large (like a space ship) was pulled into the black hole then it would hit (or float though) this layer of light particles that would seem like a very bright line crossing the ship, possibly damaging the ship due to it's intensity. …

A very quick question. What is the "empty space"* within electron orbitals in an atom? Since most of the atom is "empty space", and our world is made of atoms, than most of the stuff around us is made up of this "empty space". What is it? Does it have any properties that we know of? Is there any research being done to study it?

Ok, well I thought myself into another conundrum.... Ok, if I leave earth in a spaceship traveling 80% of the speed of light and come back in 5 years my time, then I have aged 5 years, while the earth and everyone on it has aged several decades. So, here's my question: If motion is all relative, then why do I age less and everyone else ages more? We both see our clocks running slower, however I'm the only one that time slows down for. If motion is relative, then shouldn't this be the same as the earth traveling 80% of the speed of light and coming back to me in 5 years their time?

Is transparent aluminum possible?

Here is a low quality video of the demo for the game portal that will be realised soon. http://video.google.co.uk/videoplay?docid=1299927595688205543&q=portal If you have steam installed (valve's thing for playing there games) you can view the high quality one though steam. It's graphical quite good and the physics are like most of the new games by valve (can handle meany rigid objects stacked\colliding realistically, not as stable physics as ageia) but the most incredible thing about it is it's use of "portals". There are many forums online showing many pages of "wow that incredible" type responses on every post with a few "whoa, that's like in prey" …

hi, i am doing a level physics in the uk(first year of the 2), we are doing this big coursework on the materials, where each member of the class is supposed to choose a material and make a big report on it, with plan, report, predictions, and in the end we have to have a microsoft presentation. and the project needs to be like a question, i mean the title needs to be like a question: ex. Why is Gold so expensive? Why rubber should be used for plane wheels? and things like that, all i need is a good material to start with and then i can get going myself, i didn't know what to do, so that's why i am asking people here, i am sure there are clever people who have a…

I know that the variation in Earth's gravity varies due to the following (and other) reasons: Altitude Variations in the crust density Celestial objects Distance from the equator (centifugal accelleration due to Earth spinning) But which is the most influential and what is their relative magnitudes?

I've been watching the US amazon physics bestseller list. I think I detect a shift in the market. Or maybe several shifts going on simultaneously---changes in what kind of physics books people want to buy. You may wish to comment. Here is a snapshot of the physics bestsellers (the first 20) as of 5 PM pacific Saturday 14 October. the number after the author's name is the overall sales rank among all books that amazon sells. The Smolin book has now been steady #1 for about 1 month. since about 15 September. It has been having a good sales rank, now 256 and usually in the range 200-500. Part of the shift that string books are not selling so well as they wer…

http://www.ignobel.com/ig/ig-pastwinners.html#ig2006 http://dorigo.wordpress.com/2006/10/16/the-new-ignobel-prize-in-physics/ this year the prize was awarded to Basile Audoly and Sebastien Neukirch, for their work on fractures explaining why spaghetti does not break in half: “Fragmentation of Rods by Cascading Cracks: Why Spaghetti Does Not Break in Half”, Physical Review Letters 95, 9 (2005) 95505 http://www.lmm.jussieu.fr/spaghetti/index.html you can read more about this year's prizes at the ignobel site. the chemistry prize had to do with ultrasonic velocity in cheddar cheese. the prize for medicine was for inventing an unmentionable way …