Physics

I have a spherical container (15.5m diameter, ~2000m3 volume) that is filled with salt water at atmospheric pressure. Salinity is ~35g/litre. At what temperature will the contents first show signs of freezing? And..... If ambient temperature is at the initial freezing point of the liquid, how long will it take to completely freeze the contents of the container? Similarly, if ambient is 5 degC below initial freezing point? This has stumped myself and a colleague for a couple of hours, so some help would be appreciated!! Also, explanation of workings would be helpful. Many thanks.

Can antimatter be used to destroy matter ?

Hello everyone. I sometimes get niggling questions, or half baked ideas about science/religion/philosophy or whatever that keep me up tossing and turning for oh... a good 5 minutes at night. The other day I decided I might as well register on some forums where clever people could tell me what was what, and I might actually benefit from my midnight pondering. So here goes my confused thought experiment #1: I started thinking about this after reading some article talking about the geology of the earth, please excuse any shocking beginner logical/scientific mistakes! 1. Imagine a large mass of rock in space, say the size of our moon. 2. The gravity …

is friction a conservative force or is it a nonconservative force? why?

Richard Feynman said :It is important to realize that in physics today, we have no knowledge what energy is what do you think?

if each object in the universe attracts every other object through the gravitational force, then why doesn't the entire universe collapse on itself?

http://www.youtube.com/watch?v=HzfUDHa0RJo http://www.youtube.com/watch?v=Wl4mUCYKyz4 I just thought these would be cool vids to share for my first post. Does anyone have any better vids of possible black holes? These vids have amazed me since I first saw them a few years ago on a doco on, well, Black Holes amazingly enough.

what does looping the loop mean in physics?

hi every one I have a doubt on micro cantilevers. how can i set vibration in micro cantilevers if they are not made up of piezo material? how can i detect such deflections. please respond to my question. i need the answer plz...........

In a non vaccum why do you need a larger force to move a larger stationary object. Is it because of the resitance forces you have to overcome. How is this resistance force created. In a non vaccum can I move a large stationary object with anyforce because there is no resistance.

Hi everyone. After watching/listening/reading popular science materials, some questions arise. So I'm planning to ask physics related questions here. I don't want to create new thread every time, because some of them don't deserve separate thread. 1. Which layout (?) of star-planet system on image is closer to reality? 1)All bodies in the Universe lay at one angle. 2)Bodies in galaxy lay on same angle as galaxy. Or they all lay at different angles? 2. Molecules have wave/particle duality as light does. I heard that: "The best way to think about light is that it is travels as wave, arrives as particle". Can you say the same about molecules? 3. Not…

I was looking through some old stuff and found my dads old chemistry set, there are a couple chemicals that I do know what they are, my dad was sort of mischievous as a boy:rolleyes:, so I don't want to mess around with any of these until I know what they are. I did a coulple simple experiments with them. So, I was wondering if someone could help me, The first chemical I think is a metal, because it is magnetic, solid at room temperature, conducts heat, and it possess a metallic luster, but I am at a standstill at what type of metal it is. The second chemical I have no clue because, it possess a pink-red color, and it is like powdered clay.

Why wet spots are dark?

Hi everyone. I have a stupid question about those giant 3 fan blade wind turbines. Before I start, I'm not an engineer or anything like that. I work in the health field actually, but I had a thought that has been bugging me for ages. I heard someone say that one of those giant wind turbines can generate electrical power to supply 1000 homes. Now let for argument sake, we say that each wind turbine generates 1 million watts (1 megawatt). Please excuse me if that figure is way off, (it most probably is) but it's an easy round number for the purposes of this argument. What I was thinking was this. How much power would it take for an electrical motor to turn…

On the Science of Time and on the Law of the Conservation of Energy and Matter The "quantity of force which can be brought into action in the whole of nature is unchangable". Energy or "force" cannot be increased or dimished in the whole universe. Moreover, mass or matter cannot be lossed or gained in this universe. In science, the flow of time or the arrow of time considers time to be linear. This must be true, as we have repeated and performed so many experiments and many have been proven correct because of this linear time. However, others consider time to be cyclic, and some believe time has no part in nature, that what is time is merely human invention an…

When I first discovered relativity I found it perplexing. Information travels at the speed of light but matter never gets that fast. Yet 3 bodies could be in a line moving forward. One is stationary as far as it can tell although really there is nothing definative to compare it with. The second is moving past the first at close to the speed of light with the third moving close to the speed of light past the second. They all get to being in line from having a staggered start and take a photo continuing at there relative speeds, the light from the flash reaches the finish line of this race at the same time with each body staying in the center of his bubble of light but …

I know that nothing can escape a black hole but then i heard that a positive particle and a negative particle spining together can allow one to escape the gravity of the black hole? so can any one tell me which one it is. nothing can escape black holes or can something esape a black holes.

Suppose you are to desing the braking system for a jet airplane.On its takeoff run, the jet increases its speed with a constant acceleration of magnitude. 3.5 m/(s^2) until it becomes airborne at a speed of 95 m/s.The length of the runway is 2500 m. Determine the magnitude of the constant acceleration that will stop the jet at the end of the runway, assuming that the pilot aborted takeoff at the instant the jet attained takeoff speed.

Video we made for the 2009 Nobel Prize in Physics.... I detected a slight "pure physics" vs "applied physics" tone at times!

I have been thinking, if you could possibly take a three dimetional object and put it into the second dimetion. Theoretically, that limited three dimentional object would spread out into infinity in the second dimetion. Then, if you take that infinite two dimetional object and put it into the first dimention, yet again it should be infinite. Now if you take that infinite first dimetional object and put it into the next dimention below, the zero'th dimetion, which technically does not exist? Am I very confused or have I just lost my marbles?

I know this may be a stupid question, at least for us, mere mortals. But I searched for it and didn't find it anywhere on this forum, and couldn't help to ask it myself. I mean, according to Einstein's relativity, any object in a state of movement can actually be at rest relative to another object and viceversa. So, at least in concept, the earth might as well be the one resting and the rest of the universe the one going around the earth once every single day, or am I missing something? If so, practically the whole universe would be moving exponentially faster than the speed of light. What's the explanation to this?? Please forgive my ignorance and I thank you all for an…

hi to every one. I am a new user. I am greatful to scienceforum because it is a good platform to discuss our doubts in science. I have doubts regarding vibrations. what makes the cantilever to vibrates at its natural frequency? Now a days cantilever sensors are very popularized. why people are going for cantilever based sensors?

Black holes are supposed to be able to have a charge. However, as far as I know, electromagnetic fields travel at c, so that even photons cannot escape a black hole. What about the electric field of an electron? And if we are talking quantum, what about virtual photons?

What would the gravity be like in the center of the earth? Would it make objects stretch out in all directions?

Hello, Few questions about these things.This is not homework!! 1. Is Newton's 3rd law caused by conservation of momentum? 2. If I drop a stone into a pond. The stone would exert a force on the water and the water would exert a force on the stone. So why doesn't the stone move up!! 3. Is air resistance caused by collisions with air particles. How come it takes time neutralize the force. I mean if I hit a air molecule with 10N force it would exert 10N back. So If I threw something at 10N why wouldn't it immediately stop after hitting an air molecule. I know these questions demonstrate a very poor understanding but please help me so I can improve!!Thank you!!