Physics

Is it possible for a particle to have a momentum vector pointing the opposite direction to its velocity vector? Or is that forbidden by the laws of physics?

Let's take some NP-problem: we have a verifier which can quickly say that given input is correct or not, but there is huge number of possible inputs and we want to tell if there is a correct one (find it). Such problem can be for example finding a divisor (RSA breaking) or finding a key that if we use it to decrypt the beginning of the file, there will be significant correlations (brute force attack). Imagine we have a chip with 'input' and 'output' in which is implemented (e.g. FPGA): IF 'input' verifies the problem - THEN send 'input' to 'output' - ELSE send next possible 'input' (cyclically) to 'output' such that this chip uses only basic logic gates - c…

What is the difference between energy levels and electron orbitals? And why does this occur, for example with hydrogen: n =1 -13.6 eV n =2 -3.4 eV n =3 -1.51 eV Then the maximum electrons per shell are: orbital_1 = 2 orbital_2 = 8 orbital_3 = 18 orbital_1 goes into orbital_2 4 times (n=2) goes into (n=1) 4 times

I had an idea that I thought might work but didn`t and I don`t know why? basically I wondered if I could make a sort of telescope by using a magnifying glass on the image of a distant object in a mirror, needless to say it Failed. so I tried a macro lens on my camera and that didn`t work either, I had to use the same focus distance as the object was far, in order to get a clear image. Even though the image was only a few inches away? can anyone explain in Simple Terms what`s going on? Cheers

So, I'm sure we've all seen plenty of movies where, in order to escape some enemy, Our Intrepid Hero jumps off something really tall into water below. I also recall hearing the urban legend that hitting the water from more than 90 feet up is like hitting concrete. This is obviously wrong, since the world record high dive is almost twice that (172 feet, Dana Kunze). So, what is the actual maximum height, and if nobody knows, how would it be best to calculate it, based on force, energy change, or impulse? Mokele

Is a 1 Newton of gold worth more on the Moon than on Earth?

I am trying to understand the basic concept of what ENERGY actually is. I am getting very frustrated because I cannot actually put it in to words, it just seems to be a random thing that is. However, my husband is insisting that heat is energy, and the basis of all things but in my opinion heat is just one form or result of the use of energy. I have read a definition that energy is the capacity to do work, but even that seems a bit random, where does it come from, how does it happen? Does anyone have a simplistic answer for a not too scientifically minded person. I can see where my huscband is coming from that heat causes things to happen, but surely somethin…

Hello SFN, I had a question about photons and the information they carry. We call photons "messenger particles" and they carry the electromagnetic force. When an electron emits a photon and it gets absorbed by a proton, the proton is attracted to the electron. We say, in a sort of metaphorical manner of speaking, that the photon carried a message that said "Hey! Look here! I'm an electron. You better be attracted to me." Even though this is just a metaphor, it still leaves me with a question (which I think still needs to be asked even when taken literally): How does the proton know it was an electron that emitted the photon? I mean, in the metaphor, I guess we're …

the intensity of magnetic field at a point is defined as the force experienced by a unit north pole placed at that point . WHat does unit north pole mean ???

Does fine, pure graphite block electromagnetic waves like aluminium or other conductive metals?

why does spectrum of hydrogen have many lines though it has only one electron???

Hi all,hope someone clever can help me think my questions through. I'm wondering a number of things. Firstly, what is the maximum speed a guitar string moves when plucked? To expand further, a C string for example has a fundamental wave. When pulled back and released ,the string must accelerate to a maximum speed then slow down to a stop, then travel in the reverse direction ,oscillating back and forth until it comes to rest. To complicate matters,to my understanding the string will vibrate with harmonics of which these will be integers of the standing wave. The string appears to have nodes or points at which the string is not moving but at other points it is movi…

Desiring to know how various types of energy compare to one another, I am creating a sort of game/exercise for any takers. You start with one type of energy source and its level of energy, then draw comparisons to other energy sources and list the individual amounts needed in order for their energy levels to match. I've started it with the Krakatoa eruption of 1883 that was heard in several nations. What is your prediction of the amount of energy in that sound? After figuring that out, predict what amounts the others would need to match that sound's energy. Sound: Krakatoa volcano in 1883 (loudest recorded sound in history) Fire: what size forest fire would match…

Does anyone know of a circuit design that uses 9VAC to operate an electronic switch (something like a transistor or relay) to turn on a seperate 12VDC circuit?

Having two hydrogen lazer beams cross can results in plasma being created in the air. How many of the most powerfull sort of nexus lazers would need to be crossed\what sort of focusing optics would be required to create a human visible amount of plasma?

Hello, My name is Tom - I'm new to the Science Forums. I am not a scientist - just someone who has a general interest in physics. Not sure if this is the proper area in which to ask for HELP regarding the spin of a particle. Up to now, my searches have lead me to believe that "spin" is a term that refers to a paticular "behavior" of a particle with fractional and whole number notation and does not imply actual rotation of a particle. This "behavior" could have been given any term. However, I don't quite understand what this particle "behavior" is. Any help would be appreciated. Thanks, Tom C

I would like to set up a statistcal equation to describe the probabiliity of where a particle can be found in a sphere of zero potential, and the collisions betweeen the wall and particle is perefctly elastic.

If I ram two ball together in a tube to produce some kind of energy when they collide, what material should the balls be made out of? and they need to produce and also survive to collide again....and again and so on....

I have interactive physics 04. It sucks....I want something better. Any ideas?

How does an increase in voltage with a constant DC current affect an electromagnet? Is the increased voltage just transformed into heat, or extra strength in the electromagnet? For example, at start there is an electromagnet with a current of 5A at 6V. The current is shut off, and a new supply of 5A at 30V is applied to the same electromagnet. How does the electromagnet react?

As I'm sure you are aware the various pitches in sound are classified by numbers (440 vibrations per minute=an A) so the question is as light is also a wave and color is differences in those waves are there numbers to correspond to colors? thanks for your help

can anybody advise I have not thought about heat and its definition in quite a while. does heat exist independantly of matter and radiation or are these "mediums" required to transport " joules" as we know them. The reason im asking , is that i cannot think of any instance where heat is not measured by transporting photons or particles from one physical state to another. IS THIS CORRECT?

In the early 90's a Professor proposed a theory for a "quantum Time machine" http://www.npl.washington.edu/AV/altvw45.html

Hello.I have a question wich popped up: Suppose we send two beams of red and green light(or,lets say blue and yellow light) towards a surface,and both beams are projected at the same spot?What will we see there?Some of us said we would see:yellow and green(since red+green=yellow and blue+yellow=green) while others said it is not true...The question is,do the basic ideas about colour combinations work here too or not?

i know that the atoms/molecules in a solid are less energetic than those in a liquid, and therefore vibrate less, and are hence 'solid' but i don't know how these "less energetic" atoms/molecules stick together