basics please

keu

would someone be good enough to define electromagnetism, singularity, matter and anti matter to me in a way I can comprehend, ie; the properties of each?
if thats possible?
(I know I could do a search, but a little definition would be good, thanks)

quantum bond anyone?
(I put this post here for fysh)

Fysh

Electromagnetism: "the mathematical treatment of electric and magnetic fields due to static or moving charges". (definition by Dr Klipstein, my lecturer for the subject in first year at uni). The mathematical treatment of these fields is intended to allow us to predict (and thus manipulate) the effects of moving or stationary charges on other moving or stationary charges.

Singularity - I'm not 100% on this one, I've always understood it as being a point with infinite density (as in black holes, where a star becomes so heavy that when it explodes, it collapses in on itself) , but the mathematical definition is a little more stringent as I recall. Dictionary.com offers the following (which I would agree with):
"Astrophysics -A point in space-time at which gravitational forces cause matter to have infinite density and infinitesimal volume, and space and time to become infinitely distorted.
Mathematics - A point at which the derivative does not exist for a given function but every neighborhood of which contains points for which the derivative exists. Also called singular point."

(Derivative - also known as differential - means the rate of change of some value as compared to some other value. The rate of acceleration of a person free-falling out of an airplane is the derivative of their velocity, for example. If you have a graph with a line which at some point moves only vertically with no horizontal change, that region of vertical-only change would be a mathematical singularity)

I can't think of a good definition of matter right now, so I'll go along with dictionary.com's "Physics. Something that has mass and exists as a solid, liquid, gas, or plasma.".

Anti-matter is then defined in the same way as matter, only it is made up of positrons, antiprotons and antineutrons instead of electrons, protons and neutrons.

At this point it's worth pointing out that every particle has an antiparticle. More info over here (note - this is the first site I found on Google that looked to be reasonably informative, so you may find it worth also reading other pages)

Quantum bond...heh. This might be fiddly. Basically, quantum theory predicts that a particle's properties are not fully defined until it is observed - until then there are at least two possible states for it to be in (like the old analogy with the cat in the box). It is possible to create two particles in such a way that both their properties are linked - meaning that observing one of them to determine its properties will also determine the properties of the second particle. It's hard to explain exactly how this might be done, though. Two-slit interference of light (where a single beam of light is shone on a piece of material with two adjacent slides, and the light is then projected onto a screen beyond both light source and material) can I think produce these kind of particles in certain conditions, but I'm not sure. The topic of quantum-linked particles was (and probably still is) popular as a research topic - as I recall there were intentions to use it as part of some sort of encryption system.

ecksor

Originally posted by Fysh
Mathematics - A point at which the derivative does not exist for a given function but every neighborhood of which contains points for which the derivative exists. Also called singular point."

[comment to try to relate this one to the others]: This is typically because you're differentiating a function that "blows up" at that point, i.e you're dividing by zero. While not regarded as 'infinity' in maths, I suspect that it may be treated as such in physics?

Fysh

In my experience it's treated like that sometimes, although I found that my maths lecturers in second year were very keen to stress the mathematical definition of singularity as being the one that we should use.

The problem is that it's most often used when discussing stuff like black holes where, although you have a minimum mass required for the formation of the black hole, once it's formed there's really no upper limit to the mass it can attain since the gravitational attractive force has overcome the electromagnetic repulsive force to condense it down to a very small size indeed. So you can lazily refer to it as a point of infinite density because unless you're doing calculations that's as good an interpretation as you'd need for thought experiments. Lecturers were somewhat shy about using this definition unless they were discussing something in very vague terms, as I recall. Although it does seem to be fairly popular in Science-for-the-inattentive-and-brainless-layman (sorry, but I love that phrase) books.

ecksor

That clears that up. Thanks.

keu

self employed millionaire.
don't really need science..but I can afford to be curious.

my daddy was a rich man..y'know the song

Syke

remoteviewer?

huh?

Delphi91

Originally posted by Fysh
...I can't think of a good definition of matter right now, so I'll go along with dictionary.com's "Physics. Something that has mass and exists as a solid, liquid, gas, or plasma."...

Matter is anything which takes up space, i.e. has volume.

dudara

I'd go with Fysh's definition of matter as anything that has a mass and exists in one of the state phases.

lots of things take up volumes, but have no mass, such as electric fields, etc. Including mass in the definition makes it pretty precise to me

JackieChan

If an electric field has no mass, how come its force can be measured.

maybe I'm been naive but from Aristotle we have that F=mv(Force=mass x velocity).
Since electric fields exert a force we have a non zero value for F
therefore m can not be 0.

Does this equation not apply to waves?

Fysh

Err, I think you'll find that actually forces deal with acceleration, ie F=ma.

But you seem to have misunderstood the idea behind an electric field (or indeed, fields in general). An electric field is used to describe how to electrically charged particles interact. The particle will have mass, but the field is simply the region in space in which another charged particle would experience a force due to our first particle.

Consider : The earth has mass, and as a result exerts a gravitational field. However, once you leave the earth's atmosphere, you are still subject to the earth's gravitational field.

dudara

Jackie Chan

the true definition of force comes from the rate of change of momentum. Even light waves, which don't have any mass, possess a momentum in accordance with deBroglie's Law.

So mass is not a requirement for force, but momentum is.

Steveire

i thinkn the point should be made that mass doesn't matter when dealing with electromagnetic force, but charge on the particle matters.

the four fundamental forces of nature:

gravitational force (what you use f=ma for)

electromagnetic force

weak nuclear force

strong nuclear force

these are separate and distict, but AFAIK the electromagnetic force and weak nuclear force were shown to be part of the same fundamental force called the electroweak force. Some guy won the nobel prize for it recently*, but i haven't seen much about it other than that.

* ie within the last 20 years.


wrt dudara's post, the thing about momentum is that it depends on mass, so mass is a requirement of force as you were reffering to it (ie gavintational force).

dudara

Even light waves, which don't have any mass, possess a momentum in accordance with deBroglie's Law.

Fysh

momentum in classical physics depends on mass. Once you're talking about particle physics (or quantum physics, for that matter), you have to abandon a lot of classical physics because it just doesn't work at that scale.

In the classical sense, photons are massless. However, the argument is made that, well, they have energy, and enery = mass, right? Wrong. The misconception comes from people using einstein's relation for particles moving at relativistically slow speeds (ie. not a significant fraction of the speed of light). The full version of einstein's relation is E = M C (squared) / (square root of the next bracket) (1 - (v squared/csquared)) Where v is the velocity of the particle, and c is the speed of light.

See this page for more clarification on this subject - probably better explained than my version as well.