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Yahoo and crash courses
Monday. 2.18.13 6:22 pm
Never ask a deep physics question on a Yahoo Answers forum. I'll give you a hint: there aren't any experts (seemingly of anything) who bother using Yahoo.

For anything.

During my furious and ultimately pointless study session last night, I realized something interesting. Let me begin with the obvious. Matter has potential energy and kinetic energy. Kinetic energy is easy: it's the energy an object gets from being in motion. When I throw a ball, I add kinetic energy to it. M(V^2)/2.

Potential energy is a little trickier. It's the amount of energy an object MIGHT have. It's situational; if I have a have a ball on a table, I could say it has 0 potential, or some number x, or some huge number X, depending on if I use the table, the ground, or the center of the planet as my reference point. If I "drop" it onto the table, it won't gain energy because it's already there. If I drop it from table height to the ground, it'll have x joules of kinetic energy when it hits. If I drop it to the center of the earth, it'll have...a lot more kinetic energy when it hits.

Potential is based purely on position and acting forces. Kinetic is based purely on mass and velocity. Energy flows between one and the other. If I hold my ball over the ground, it has x potential and 0 kinetic. After I drop it, right before it hits the ground, it has exactly 0 potential and x kinetic energy. Pretty cool.

So we're studying electrodynamics. It's time dependent electronic and magnetic fields, and how they get mixed up. A single charged particle creates an electric field, sort of like gravity (except gravity always attracts, but electric fields can repel). If the charge is moving, it creates a magnetic field, which is pretty complicated. I'm skipping a lot of stuff, but basically when you put the two together you can get crazy things. If I drive a current through a loop, it creates a magnetic field. Let's say that field goes through a different loop that isn't connected at all to the first loop. If my current changes, the magnetic field changes, and that changing field drives a current through the second loop.

That's pretty cool, but it's not my point. Another effect is that if there's a current, the field lines from the first loop are actually affecting it as well. If I try to change the current, the changing field lines make a new current that counters the change I've made. It's called self-inductance, and it's sort of like inertia, the property of mass that makes it want to stay the same speed. The current wants to stay the same. In fact, if I call the inductance L and the current I, then the energy I have to expend to create the current is L(I^2)/2.


Inductance acts just like inertia, and the energy stored in a magnetic field looks and acts the same as kinetic energy.

As for stationary charges, the energy I have to expend to make a configuration of charges (for example, holding together two charges that don't want to be close) is related to their position...and the force that they exert on each other.

Do you see what I'm getting at? Kinetic and Potential energy of matter correspond to electric and magnetic energy, respectively.

That's about as far as I've taken the parallel. Not very exciting. :D Have a good day guys.

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Sunday. 2.17.13 10:58 pm
This weekend has been drenched with studying and...snow? I must have slept through it.

I have a headache from reading and glaring into the sun too much.

I just realized I got a somewhat unsatisfactory grade on my Friday test, and now I'm extra prompted to do well tomorrow. SOOOOO

This is all you get. Sorry I'm not sorry!

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Saturday. 2.16.13 6:23 pm
I don't feel like posting. Nyeahhhhh

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Saturday. 2.16.13 12:25 am
What a long day:

8 - 10; Wake, study, eat, walk
10 - 11 AM; Astronomy Test
11 AM - 12 PM; Electrodynamics Class
12- 3 PM; Working in the lab
3 - 4; Sociology Class
4 - 5:30; Walking, eating, and my free time
5:30 - 7; Family time
7 - 10; Friday Night Devotional and hanging around
10 - 12; IHOP with riddles

As you can see, I keep a heavy Friday rotation. It's weird, I seem to be busier on the weekends than during the week. Oh well. You see that half hour of free time around 5? I spent that writing up cards that the guys gave to the GT/Emory sisters during family time. So yeah.

IHOP was originally a way to put food into my stomach. But then one guy wanted to come. And then my whole car wanted to come. And suddenly nine people were coming. And somehow we spent almost TWO HOURS sitting at the table, just joking around and telling riddles. It was a rare moment where I wasn't aware of the passage of time. Definitely a lot of fun, and I was able to bond with some of the guys I don't see as often (i.e. don't live with).

I'm...really tired.

I have to drive home next weekend to get my driver's license renewed. It expired on my birthday, and I can't do anything about it here in Georgia. Ironic. I have to make an eight hour round trip to fix the thing so I don't get ticketed for driving without it.

mmmm bed now kiddies

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