SuperCioci@

Where did the pineapple come from ?!

Does international law forbid soldiers / armies from NOT wearing distinctive military insignia (such as the flag of the country they belong to)?

References please.

Thanks

Someone is sitting on a stool with a wheel spinning in, say, the clockwise direction (the axis of rotation is vertical). The guy then turns the wheel upside down, so that it is now spinning in the counter clockwise direction, and the person himself starts rotating in the clockwise direction:

http://www.youtube.com/watch?v=eLRFsy0fOTE

I understand this is due to the conservation of angular momentum, but I was thinking:

if the guy started moving with the stool, then something must have applied a torque on him?

Motion is always caused by a force right? So where did the force that started the rotation of the guy on the stool come from?

Thanks

Does air embolism only occur when someone is scuba diving? I.e. breathing air mixed with gas from a tank?

If yes, does it have to do with some gases in the tank?

Why can't there only be Oxygen?

So in apnea diving there should be no risk of air embolism upon ascent?

What is the minimum depth from which one could re-emerge safely without having to wait?

Hello everyone.

So I start my computer, type my password, and it says "Starting...".

When the desktop is supposed to come up, there is a blue screen instead.

Just blue, nothing written on it.

After about 10 minutes, this blue screen vanishes and the desktop appears, and everything works OK.

What can be causing this?

How can I solve it?

Thanks in advance

what is the electric field generated by a particle that is CONSTANTLY and LINEARLY accelerating (i.e. that does NOT stop to move at constant velocity, which is usually the approach used to calculate the transverse field emitted as radiation)?

What would it look like and how would one go on about calculating it?

Thanks

A cone with aperture alpha, centred on the z axis and with UNIFORM charge density.

I used the general solution to Poisson's equation and got an expression for the potential at any point r, in spherical polar coordinates, so in terms of r and theta (no phi dependence because of the symmetry of the cone).

My problem is: when I set theta equal to the aperture of the cone, which corresponds to calculating the potential of the points ON the cone's surface, I do not get a constant, but something which varies with r.

Now, conductors should be equipotential surfaces shouldn't they?

So why don't I get a constant on the surface?

Or rather: since I know that charge accumulates in the sharp regions, could this example be physically unrealistic since it is considering a UNIFORM surface charge density? Could this explain the non-constant potential on the surface of the cone?

Many thanks.

I'm trying to get "An introduction to quantum physics" by French and Taylor but I can't find anywhere.

Help pleassee?

To anyone who has done experiments in X-ray crystallography in the past.

We are bomarding copper with high energetic electrons, thus forcing it to emits the K-alpha and K-beta characteristic radiations ( X-rays) and some background. These are shone on and scattered by a crystal. We detect the intensity of the diffraction pattern as a function of the angle of declination of the crystal.

We get a graph with 2/3 sets of double peaks. This makes sense, since each doublet corresponds to the K-alpha and K-beta emission, and each set corresponds to when constructive interference occurs.

What I don't get, is why these peaks get lower with angle. That it, at large angle of declination of the crystal, we get less intense peaks. WHYYYYY?

In this graph:

http://en.wikipedia.org/wiki/File:TubeSpectrum.jpg

the background radiation, as far as I understand, is the Bremsstrahlung radiation.

Why does it have a maximum at short wavelengths and then decreases??

thanks

For example. In a cloud chamber, when an ionising radiation passes through the vessel, the alcohol condenses on the trail left by the particle. What does this physically mean? Does the incoming particle (say, a muon) knock off an electron thus forming an ion? Shouldn't the muon be deviated then? And what if the incoming particle were an electron itself??

This question arises while I was studying how a silicon detector works: apparently it's the same principle, but I don't get how the incoming radiation (alpha particle, beta particles) can actually cause the creation of ions without its path being deflected...

http://www.wolframalpha.com/input/?i=expand+tan%C2...

Anyone know how can we mere mortals get the expansion WolframAlpha got?

Is there a general rule/method to produce power series of functions about their singularities?

Ho un cavo VGA, quando lo uso per collegare computer a tv sulla televisione vedo solo lo sfondo del desktop (vale a dire un secondo schermo)

Come faccio a vedere lo STESSO schermo che vedo sul computer.

ogni passo per favore (windows XP)

Conoscete un programma gratis e facilmente scaricabile per inserire delle scritte su un filmato?

Mi spiego meglio: ho questo filmato fatto da diverse tranches e negli intramezzi vorrei inserire una "slide" (sfondo bianco o di qualuque colore) con una scritta... e se possibile anche scritte sul filamto vero e proprio.. grazie

I really don't understand what STEPS to follow to do this problem.

We have a plank of length 6.0 m, which is held by two sawhorses at a distance 1.5 m form each other and 0.75 (each) from the centre of the plank. On the left end of said plank there is a mass of 90 kg, while on the right end there is a man. How massive should this man be in order for the system to be balanced?

Now, my book says that "in order for the system to be balanced the centre of gravity should coincide with the right sawhorse". Why??

Thanks

a slender uniform rod is rotating around one end. length = 1m, mass = 50.0 g

A bug sits at the other end of this rod, and has mass 10.0 g.

It jumps off the bar with velocity 20 cm/s.

What is the angular velocity of the bar after it jumps?

Now, I think I am tackling the problme the wrong way, using the wrong formluae... what would you do?

thanks

Salut à tous:

quand je démarre mon ordi tout se passe normalement jusq'à quand le desktop apparait: j'ai un Windows 7 Pro, mais le fond d'écran devient noir et la barre des applications en bas devient grise et semble celle d'une version antérieure de Windows. Tout icone présentes sont des applications: tous les données (word, excel etc.) sont disparue. Dès que le Desktop apparait, il y a ce message:"Echec de connexion à service Windows. Windows n'a pas pu se connecter au service Service de notification d'événement système. Ceci empeche les utilisatuers standard de se connecter au système."

J'ai déjà essayé à le démarrer en mode sans échec, mais la seule différence est que le message n'apparait plus et que les données et les documents reapparaissent.

Conseils?

Hi everyone, I was studying the cyclotomic equation and I came across an example:

x^4 + x^3 + x^2 + x +1 = 0 ; this equation cannot be factorised neither using Ruffini's rule nor replacing an x with t. The book said that it is sufficient to divide all by x^2 and rearrange the terms to obtain --> x^2 + 1/x^2 + x + 1/x + 1 = 0, then let w be equal to x + 1/x, and the equation (I also have verified) becomes w^2 + w -1 = 0.

My question is: does it exist a formula (or a procedure) that allows to reduce an equation with a degree greater than 2 to a quadratic? Procedures other than replace x^4 with t and x^2 with t.

In fact there would be Abel-Ruffini theorem to take into account...which says that there is not a general algebraic solution for quintic equations and higher degrees...

Could you help me please?

Hi everyone, I was studying the cyclotomic equation and I came across an example:

x^4 + x^3 + x^2 + x +1 = 0 ; this equation cannot be factorised neither using Ruffini's rule nor replacing an x with t. The book said that it is sufficient to divide all by x^2 and rearrange the terms to obtain --> x^2 + 1/x^2 + x + 1/x + 1 = 0, then let w be equal to x + 1/x, and the equation (I also have verified) becomes w^2 + w -1 = 0.

My question is: does it exist a formula (or a procedure) that allows to reduce an equation with a degree greater than 2 to a quadratic? Procedures other than replace x^4 with t and x^2 with t.

In fact there would be Abel-Ruffini theorem to take into account...which says that there is not a general algebraic solution for quintic equations and higher degrees...

Could you help me please?

integral of x/(x^2-4) from -sqrt3 to 0.

In my opinon, it should be ln2...what do you think?