stupid particle physics questions...

Man, I have been up all night trying to figure out this crazy-ass homework, and I’ve actually succeeded (thank you internet) on 32 out of 34 of these hellish problems…

These last two read like they’d be the easiest/most obvious of them all, but I just cannot seem to find anything that addresses them in a way that I can understand, including this laughable excuse for a book. If anyone can help me out (by explanation, by direction to a good website, anything at all), you’ll have forever restored my faith in humanity.

First one:
An electron participates in:
a) strong force only
b) strong & weak force only
c) electromagnetic & gravitational force only
d) electromagnetic, gravitational, & weak force only
e) electromagnetic, gravitational, & strong force only

(If it was an option, I’d have said all of the above! :confused:)

Second one:
A particle can only decay to particles with greater rest mass
a) if antiparticles are produced
b) if photons are also produced
c) if neutrinos are also produced
d) if the original particle has kinetic energy
e) never

(I’m not even sure what “rest mass” IS…)

er, that is, :confused: …weird disembodied smiley-head, there…

I won’t answer them as it’s your homework but I’ll give you enough information to answer them:

The stong force is the attraction between nucleons and quarks, the electromagnetic force is the attraction/repulsion between charged particles, gravity is the attraction between massive particles and the weak force affects leptons and quarks.

The electron is a massive charged lepton

  1. The conservation of mass-energy means, where RE is the rest energy obtiane from E = m[sub]o[/sub]c[sup]2[/sup], where m[sub]0[/sub] is the rest mass of a particle (i.e. the mass of a particle at rest):

K.E.[sub]in[/sub] + R.E.[sub]in[/sub] = K.E.[sub]out[/sub] + R.E.[sub]out[/sub]

Cool, I was just about to post saying I thought I had figured out the second one; that confirmed it for me.

And the first…
so I would guess that it’s electromagnetic, weak, & gravitational? Weird…I never thought of an electron as “massive” at all; in fact I thought it was the smallest of the three main particles. Oh well, goes to show how far logic takes you in physics… XP

Thanks for your help!! Faith in humanity duly restored. :wink:

Yes you’re correct, the electron is small comapred to the proton and neutron, but it does have mass, therefore it is ‘massive’.

Massive simply means having mass. Any particle with mass is called massive. Particles like photons, which have zero rest mass are called massless. Even though an electron is about 1/2000[sup]th[/sup] the mass of a proton, it’s still called a massive particle.

first thing, i’m just guy who sometimes reads books on this stuff.

first one is c i’m guessing. here is my reasoning an electron can’t be split anymore and still be a particle, so i don’t think the strong force counts. it orbits the nucleus becouse of an electromagnetic attraction, not the weak force. so i think we can rule out weakism.
leaving c electromagnitism and gravity.
second one is d i’m guessing. a-c violate conservation of mass and energy. d however does not. if your particle has energy there is no reason that i know of an unstable particle could not, if the condition were right, convert some enery to mass when decaying.

hope this helps

A nitpick: I assume that by “three main particles” you mean electron, proton, and neutron. If you’re talking in physics terms, though, the three main types of particles are massive fermions (including the electron), neutrinos, and quarks. There are three types of massive fermions, three neutrinos, and six quarks. Over the past five years, in fact, a huge amount of evidence has led most physicists to believe that neutrinos actually have a very small mass (something like 1/50 000 the electron mass), instead of being massless as was previously thought, so the electron isn’t even the “lightest particle”.

You have the wrong answer for the first one, electrons are involved in weak intercation the most obvious example being beta decay in which a down quark in a neutron decays into an up quark (still confined to the nucleon which becomes a proton), an electron and an anti-electron neutrino.

quarks are massive fermions.

You can divide the particles up sevral ways: gauge bosons, leptons, baryons and mesons or gauge bosons, leptons, quarks would both be standard ways. gauge bosons are bosons, leptons are fermions, baryons are hadrons which are fermions, mesons are hadrons which are bosons. Hadrons are particles made out of quarks.

Except that the reaction has to be valid in any reference frame. If the reaction can’t happen in the center-of-mass frame (particle at rest), or any other frame, it can’t happen at all.

i see. i forgot about the ego-centric, everything moves but me, nature of matter. the particle being able to convert kentic energy to mass without direct interaction of another body would violate newtons third law. i stand corrected.

Your right swansont, i didn’t even think about that.

a massless photon can decay into an electron and a positron, but the reaction needs to be mediated by other matter. A photon in a vaccum decaying would violate the conservation of momnetum-energy which is invariant under Lorentz transformations.

Closed at the request of the OP.

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