Annemarie

Another annoying this about the ipod This is really annoying! I have a number of spoken word files, inclding the Feynmann lectures, frnech lessons and other things that I enjoy listening to. Even though there is an audio book section, I cannot find a way to transfer these files to that section, which means that they are treated by the ipod as normal song files, so when I'm listening to all 2,000 of my tracks, very now and then I get the booming voice of Richard Feynmann and jump up in alarm, before skipping to the next song. Does anyone know a way to transfer these files out of the song respoitory to the audio books one?

~What do you mean by a perfect frame of reference? I thought you would experience all of those effects when you are travelling at c, or is that what you mean? In that case, why is travelling at c called being in a perfect frame of reference?

The seeds that get carried away by the wind or any natural reason, will be more sucessful. Surely the tree needs leaves to extract energy from the sun, but yes also to provide shade for roots. The tree would ideally like the largest surface area to absorb as much of the suns rays as possible, leaves are flat and large.

I'm going to get a scanner, I think I have pretty much considered all the possibilities, so you need to see it. I do have an additional problem. As I mentioned before I'm reading the Feynman lectures to expand my own knowledge and I've just foudn something that doesn't make so much sense again. Chapter 15 part 1, Feynman is talking about relativity, and he says that the speed of light waves is unaffected by the velocity of the emitter, which I'm totally cool with, then he says "This is analogous to the case of sound,. the speed of sound waves being likewise independant of the speed of the source". Erm, that doesn't make sense to me, I thought the Doopler shift was the key thing there to do with sound waves being emitted from a moving source, where it's wavelength and frequency change according to the speed of the source, and therefore the speed of the emitted waves is changed....?

Theres really no point in any replying unless they can see a copy of the lecture notes. He's definatly not just using it as legnth because he actually uses the length p to cancel with a real density p.

Simply put. The earth is not hollow for this reason. When you get an earthquake, the p n and s r or whatever waves ( I don't know too much about that part of it being a physicist) travel at different rates through the earth due to the varying densities of it's layers, if it was a vacume, then these vibration waves wouldn't travel through its center. And don't try to say that the waves travel along the surface, because it cannot work that way due to the frequency shift of the received waves and well look it up. http://www.yorku.ca/esse/veo/earth/sub1-10.htm Also, I mean its just ridiculous the suggest that the Earth is a vacume because the gravity just wouldn't work, if the Earth's actual mass was significantly reduced due to you scooping out it's inside it's angular momentum would drastically be made smaller and it would just spiral into the Sun, it wouldn't be able to maintain orbit.

A Lepton, is one group of fundamental particles of the universe, Quark is the name of the other group. In each group there are 6 fundamental particles, and 6 of their anti particles. Most of the matter that you see around you is baryonic material, you see Leptons can exsist on their own, for instance the electron, where as quarks team up to form baryons or mesons. A meson is a pair of quarks and a baryon is made of three quarks. A proton is made up uud (u-up, d-down, these are some of the names of particles called quarks which partically make up an atom), and a neutron is made up ddu, this is called baryonic matter because it's made of baryons, also we cannot touch or interact with all of the fundamental particles and some of them are very mysterious. They make up everything in the universe and it's the most inspiring and compelling thing to study. I haven't really even scratched the surfae, but don't be afraid to dip into a few websites and text books, you'll find the information much more friendly than you would expect. But alike you I have no idea how the names match the profiles. Take care

Another key point here is that electrons weigh 10^-31 KG, and are TINY, it's not possible for us to ever "see" an electron, in the tradition sense of a photograph (this is because the wavelength of light that is visible to us has too long a wavelength to be diffracted opr affected in anyway by the presense of an electron in it's path, and when a photon is incident on an electron the interaction that occurs, (bound free absorbtion or scattering, in any number of processes), we still won't be able to "see" it. Therefore it has no "shape". The pictures that you have seen are visual representation which try to help us recall the information more clearly, visual aids always help, but they're not true to the quantumness of the atom.

Chapter 13 part 4, Gravitational field of large objects, (page 13-8 in the commemorative edition) Just a foreword, I'm not trying to prove Feynman wrong and I'm expecting to be shown where my own judgement has let me down. I don't understand why Feynman has used p (roe, density) for the length if the mass per unit area is constant. I can see how length wise r^2=p^2+a^2, it's just pythagerous, but how can a length unit be equivalent to p, density? I don't understand. Whats more interesting is that when I use my own method of finding the field, I find exactly the same answer. Odd or what? Oh and if anyones wondering why I'm still studying the Feynman lectures even though exams were ages ago, well I've decided that before my third year starts I want to have studied as much as possible so I can concerntrate on my dissatation, but I still have no idea what to do it on...

I don't think religion has anything to do with physics, personally I think when the two mix it generally has bad concequences. Also when physics mixes with anything except what it naturally should.

I hope thats the right equation, but it doesn't really mater if it isn't because it was given in solutions to a piece of coursework, and if thats what my lecturer thinks it is, then if I use a different equation then he would mark it wrong, so I'm going to use it in my exam. I think it is diffusion though, I mean, the gamma rays are diffused by the lead particles. Their intensity is reduced.

Hertfordshire

At the speed of light some amazing things happen, firstly your mass when you're travelling at c will go to infinity, i.e. you will exsist at all points in the universe simultaneously. Also you shrug off all of the forces you meet in everyday life, below c. For insance electromagnetic forces gravitational etc... are all lost and there are proofs for all these things. When I'm done with my degree my masters and phd it's my life long ambition to create a time machine. A little extravagant, pretencious and far fetched, I have a feeling that it is possible, I want to find out if it is. All that I try to remember when setting my sights on something that is currently unattainable, is that when they were going into space, who thought they could? People said it was impossible and they never would.

The law that governs this kind of problem (the intensity problem) is Fick's Law I=Io e(-uX) Io- Origonal Intensity I- Final intensity u- Some constant which can be determined when you know two other piece of information, u varies from one material to another X-Length of the shield

I just want to say that today is my last exam, it's High Energy Physics and Astrophysics (and the other exams I've had have been Optical Physics and Spectroscopy, Thermal and Condensed Matter Physics and Electromagnetism and Mechanics), I'm really nervous. But after 5-15 today I will have a year and a half in which I'll be doing some physics work but I'll mainly have a shed load of free time. I'm going to be doing a little bit of work to earn some money, thankfullly I've got a good job with St. John's Ambulance, as one of those peky tabbard people trying to get you to ive your money to help others, but honestly all we want is your money and then you can get on with your lives again! Anyhow, I've been considering lots of different possibilities of what to do with my spare time, I am definatly going to do something to do with physics to enhance my knowledge. I'm also going to learn French and try to advance in my piano playing. It's the nicest feeling in the world knowing that soon you'll have nothing to do, no responsibilities, nothing to worry about. Just free time. *sigh* So anyway, if anyone has any suggestions let me know. Also, I always used to use the How Stuff Works forum, now I'm going to adopt this as my new forum home, I think I recognise quite a few names from other forums, espcially Swansont, which can't be a regular name. Anyhow wish me luck and thankyou again for your help!

I don't think you meant to ask, why do electron spins exist. Becasue thats like asking why do humans exist. Well know one knows. But the question is, even though all atoms have electrons with spin, why do some exhibit magnetic properties and others not. Well, there are two main groups, rare earth metals (lanthanum to lutetium) and the iron group. I will now talk about energy levels within the shells of electrons of an atom. A stable atom will have filled shells and subshells, that at least makes it less reactive because for any filled shell or subshell the net angular moment and spin is 0. In the rare earth group metals, there is an incomplete 4f subshell, meaning the electrons within will be effected by a magnetic field, their dipoles becoming aligned and they exhibit paramagnetic behaviour, but this subshell is shielded by two outter complete shells 5s and 5p, so the electrons are not affected by interactions with other atoms. For Iron their outter most subshell 3d is incomplete, meaning that the electrons will be interacting with it's neighbours, which results in ferromagnet behaviour. I would love to sit and write all about these two complex yet beautifully simple concepts, except I have an exam tomorrow and I keep on getting dsitracted by this website. Richard Turton's "The Physics of Solids" is a good text covering magnetism super conductors and everything else surrounding the subjects.

The universe could go three ways, due to the two major forces that are acting on matter on a macroscopic scale. Firstly, if the universe is expanding quickly enough there will come a point when the gravitational force thats holding everthing together will not longer be able to, the universe will expand until even the atoms split apart. The point at which the universe started expanding was the big bang and continues for ever results in a universe which is a soup of particles at an equillibrium temperature. This is called an "open universe" Scondly, the Universe may start slowing down in it's expansion, ie not enough kinetic energy to over gravity, and as you rightly stated we'll have a "big crunch", this is called a "closed universe" Thirdly, kinetic energy and gravitational energy could reach equillibrium, i.e. no explosive ending just the universe chilling out, a "flat universe". We will be able to find out which fate awaits us in a couple of thousand years, by tracking the universes expansions through red shitf. Hubble (a very clever and inspiring man) founded a law to determine the age of the universe and its fate. v = H r v- Recessional Velocity H- Hubles Constant r- Distance So from measuring the recessional vlocity of a star, you can calculate it's distance and the inverse of the Hubble Constant is the age of the universe. So the more measurements made the better the idea we have about it's age. Once we know the universes age and it's expansion rate we can extrapolate the kinetic energy gained at the big bang. The final state of the universe can be define by a constant w. w is the ratio between the current density of the universe and the critical density, if w=1 the flat, w>1 closed universe and w<1 open. Check out http://superstringtheory.com/cosmo/cosmo21.html and http://hyperphysics.phy-astr.gsu.edu/hbase/astro/hubble.html#c1 for more info

An absorbing lead sheild of 3 cm thickness reduces the intensity of a narrow beam of gamma rays to 10% of its origonal intensity. a) Is this process a quantum tunnelling one? b) What thickness is required to reduce the beam to 0.1% of it's origonal intentisty? c) What is the half-thickness, reducing the intensity to 50% d) How much is the intensity reduced if a 5cm thick sheild is used? e) Given that 10^15 gamma photons are incident, can you specify how thick a lead shield would have to be so that not a ingle gamma photon can pass it? The problem is I know that I have enough knowledge to answer this question, I just can't quite get my head round it. It's funny the things you get mental blocks on. In quatum tunnelling the amplitude is affected only (i.e. not the wavelngth of the particle), while the particle is "tunnelling" through the barrier it's amplitude decreases exponentially. I also know that intensity is proportional to amplitude squared. But now I'm stuck. Annemarie

I have my second year exams for Physics tomorrow and I've got something mixed up in my mind, and I'd really appreciate it if someone could set me straight. Why is water more effective than lead in slowing down fast neutrons? Also why do neutrinos interact weakly with material? (Their detection is proof enough that nuclear reactions are taking place, detection units are constructed and then taken under ground so as not to have the weak neutrino signal interferred with by other particles) Cheers. Wish me luck!