## Search found 46 matches

- Tue Oct 25, 2011 5:33 am UTC
- Forum: Science
- Topic: Physics Question: Lagrangian Density and Fields.
- Replies:
**0** - Views:
**710**

### Physics Question: Lagrangian Density and Fields.

http://img641.imageshack.us/img641/2023/29399786.jpg I have this question for an advanced physics unit I'm taking, and I'm really not sure how to start it. We had a guest lecturer teach us about this stuff for 8 lectures, but I'm still really confused by it all. For a, do I find the energy current ...

- Tue Sep 27, 2011 3:01 pm UTC
- Forum: Science
- Topic: Looking for material on Electrodynamics
- Replies:
**16** - Views:
**3619**

### Re: Looking for material on Electrodynamics

Thanks Macbi, they were pretty cool! I'm yet to comb through them properly yet though. Thanks for the advice tooyoo, I know everyone is trying to help, I appreciate any advice! I should have mentioned I often use the library and pick out as many books as I can, but almost all of them skip steps here...

- Sun Sep 25, 2011 3:23 pm UTC
- Forum: Science
- Topic: Looking for material on Electrodynamics
- Replies:
**16** - Views:
**3619**

### Looking for material on Electrodynamics

I'm not sure if this is inappropriate, if so please let me know. In the past I've found an advantage in looking over different peoples perspectives on certain topics in physics, mainly because I don't think I'm all that clever, and I often have trouble using only one source since I don't see a lot o...

- Sun Sep 25, 2011 2:59 pm UTC
- Forum: Science
- Topic: Re: A question about orbits... [Solved]
- Replies:
**8** - Views:
**1820**

### Re: A question about orbits... [Solved]

Thanks guys, you were all fantastic help!

- Sun Sep 25, 2011 3:40 am UTC
- Forum: Science
- Topic: Re: A question about orbits... [Solved]
- Replies:
**8** - Views:
**1820**

### Re: A question about orbits... [Solved]

I'm curious in what magnitude of mass an object would need to have its own orbit. Or is it only a question of density? There's a whole bunch of information on how to calculate escape velocities and such, and I've tried using that to derive a way to find what sort of mass you need before you start ge...

- Thu Feb 10, 2011 7:48 am UTC
- Forum: Science
- Topic: Career prospects for a physics/math major?
- Replies:
**11** - Views:
**3446**

### Career prospects for a physics/math major?

I'm beginning my second year of a physics math major. I intend on continuing math and physics through to third year, and at the moment I'm inclined to do my honors in theoretical physics. My marks are reasonably good, and I'm enthusiastic about both fields, particularly physics (though first year wa...

- Fri Sep 24, 2010 2:59 pm UTC
- Forum: Mathematics
- Topic: Doubts about my physics study: am I smart enough?
- Replies:
**19** - Views:
**5717**

### Re: Doubts about my physics study: am I smart enough?

I came out of high school having only done art and music. Decided I wanted to do something academic, always really found physics interesting and so I learned the math I needed through the holidays on my own, much like you did, took a few exams and was given entrance to a bachelor of science major in...

- Wed Sep 22, 2010 12:46 pm UTC
- Forum: Mathematics
- Topic: Linear ODEs
- Replies:
**7** - Views:
**1283**

### Re: Linear ODEs

okay so i see this is quite a broad topic! well how about for now we stick with linear first order ODE's? I have this problem which I can't work out.. (x^2+1)dy/dx - (2xy) = (x^3+x) for some reason it's not working well for me, though I'm probably just tired. for the integrat...

- Mon Sep 20, 2010 12:43 pm UTC
- Forum: Mathematics
- Topic: Linear ODEs
- Replies:
**7** - Views:
**1283**

### Re: Linear ODEs

Thank you nimblefinger, that really cleared a lot up for me. Your last note was especially helpful too. I know it's obvious, but it's the sort of thing I'd never had thought of. Hopefully I'll get a lot better at these as time goes on. Are these the trickiest of the four types of ODEs? Homogenous OD...

- Mon Sep 20, 2010 10:47 am UTC
- Forum: Mathematics
- Topic: Linear ODEs
- Replies:
**7** - Views:
**1283**

### Linear ODEs

In calculus we're currently learning about different types of ODEs, first of which being linear ODEs. I think they're pretty neat, a little bit tricky though. There are four different types of ODE's right? Well I have a home work question, but i'm pretty confident I've solved it. Just looking for co...

- Mon Sep 20, 2010 10:37 am UTC
- Forum: Mathematics
- Topic: Teach me integration by substitution
- Replies:
**3** - Views:
**1212**

### Re: Teach me integration by substitution

Thanks you guys, this actually helped significantly. If anything, this was really easy.. Especially integration by parts. I think I just needed the motivation to learn it. Now to apply it to my linear ODE's which I'll ask about soon...

Thanks again, guys!

Thanks again, guys!

- Sat Sep 18, 2010 5:31 am UTC
- Forum: Mathematics
- Topic: Teach me integration by substitution
- Replies:
**3** - Views:
**1212**

### Teach me integration by substitution

I'm in the last unit of mathematics for a first year physics degree, and I managed to get by without completely learning integration by substitution and by parts. I'm not kicking myself seeing as I really need it just to do the basic steps of all the theory we're learning now, i.e. ODE's in linear f...

- Sun Aug 22, 2010 2:58 pm UTC
- Forum: Science
- Topic: On the subject of Astronomy
- Replies:
**5** - Views:
**1197**

### Re: On the subject of Astronomy

Yes, sir! I think I just needed a little push. Here I come, Amazon haha.

Did Hawking do something similar to cosmos, or am I mistaken? Masters of the Universe or Origin of the Universe?

Did Hawking do something similar to cosmos, or am I mistaken? Masters of the Universe or Origin of the Universe?

- Sun Aug 22, 2010 10:29 am UTC
- Forum: Science
- Topic: On the subject of Astronomy
- Replies:
**5** - Views:
**1197**

### On the subject of Astronomy

I have no history or experience in astronomy. I'm enrolled in a physics and mathematics degree, and am first year. I intend on doing relativity and cosmology in 3rd year, and so i'm doing "advanced astronomy", and skipped straight to this without doing basic astronomy because i had the mat...

- Wed Aug 11, 2010 1:44 pm UTC
- Forum: Mathematics
- Topic: Basic astrophysics - homework question
- Replies:
**10** - Views:
**1933**

### Re: Basic astrophysics - homework question

I'm still struggling, but you guys are awesome for helping out. You especially, PM 2Ring! Will let you guys know once I sort myself out or if I have any more questions, but I think I'm getting somewhere.

- Sat Aug 07, 2010 7:01 am UTC
- Forum: Mathematics
- Topic: Basic astrophysics - homework question
- Replies:
**10** - Views:
**1933**

### Re: Basic astrophysics - homework question

I think I'm a little out of my league here. I'll speak with some of the math staff and see if they can help me out. I'm sure it's simple but i'm stressing out! Thanks for your help, you guys!

- Sat Aug 07, 2010 3:18 am UTC
- Forum: Mathematics
- Topic: Basic astrophysics - homework question
- Replies:
**10** - Views:
**1933**

### Re: Basic astrophysics - homework question

I've not heard of it before, but I'm sure I could learn it. Would that just be a case of using a definite integral with 4pir^2 out the front? Sort of like Integrating volume, or revolving a function about the x axis to get a 3D solid?

- Sat Aug 07, 2010 1:38 am UTC
- Forum: Mathematics
- Topic: Basic astrophysics - homework question
- Replies:
**10** - Views:
**1933**

### Basic astrophysics - homework question

I'm in my first year of physics/mathematics, and with the one unit of physics and one unit of math i've completed I was allowed to enroll in an advanced astronomy class. We've literally had one lecture on the topic of stellar structure and received an assignment on it, but I'm feeling way out of my ...

- Mon Jun 28, 2010 4:17 am UTC
- Forum: Science
- Topic: basic physics/math problem [Solved]
- Replies:
**10** - Views:
**1895**

### Re: basic physics/math problem

How interesting, thanks for explaining all of that, you guys. I will now step away from this problem haha.

- Mon Jun 28, 2010 4:14 am UTC
- Forum: Science
- Topic: The math of string theory [Solved]
- Replies:
**3** - Views:
**1289**

### Re: The math of string theory

Sorry, i do realize that was a very vague question, though that comic and these lectures have more than answered my question! Thank you.

- Sun Jun 27, 2010 3:55 pm UTC
- Forum: Science
- Topic: The math of string theory [Solved]
- Replies:
**3** - Views:
**1289**

### The math of string theory [Solved]

I'm very curious to see what the mathematics in string theory looks like. Also, my lecturer tells me that one problem in quantum electrodynamics might take about 3 days to solve! unfortunately I don't get to do any of this stuff for another year, and i can't really find anything in google. so i gues...

- Sun Jun 27, 2010 3:46 pm UTC
- Forum: Science
- Topic: basic physics/math problem [Solved]
- Replies:
**10** - Views:
**1895**

### Re: basic physics/math problem

haha sweet, thanks dude! i thought this sort of a question would be really cut and dry to answer, evidently not. what sort of area does this come under? thermodynamics and fluids?

- Sun Jun 27, 2010 12:57 pm UTC
- Forum: Science
- Topic: basic physics/math problem [Solved]
- Replies:
**10** - Views:
**1895**

### Re: basic physics/math problem

okay so how would i solve that mathematically? again, i haven't done thermo or a lot of math yet. i think i've seen differential equations which describe this kind of thing, but i think i'm way off. is this too difficult a problem to do with my knowledge at this point? if i saw the math i could prob...

- Sun Jun 27, 2010 4:52 am UTC
- Forum: Science
- Topic: basic physics/math problem [Solved]
- Replies:
**10** - Views:
**1895**

### basic physics/math problem [Solved]

A friend of mine asked me a question the other day, and as simple as it is, i'm not sure how to solve it. The question was, if we have a 3 meter cubed block of water, how long would it take to freeze if she put it in an industrial freezer? I guess the freezer would be like -5C or something? it was a...

- Fri Jan 01, 2010 3:19 pm UTC
- Forum: Science
- Topic: Motion in a straight line (Physics)
- Replies:
**28** - Views:
**3164**

### Re: Motion in a straight line (Physics)

Ah that's rad, thanks a lot everyone! I really appreciate all of your help and advice. A little bit irritating that it took me so long to get, but i'll certainly work on it!

- Thu Dec 31, 2009 6:58 am UTC
- Forum: Science
- Topic: Motion in a straight line (Physics)
- Replies:
**28** - Views:
**3164**

### Re: Motion in a straight line (Physics)

It is just a quadratic! Oh, man, I'm so bad at this. So I worked it out using the quadratic equations and got the answers -1.12 sec and 7.24 sec. So I assume that I can't have a negative value for time, because that's silly. So the answer would be 7.24 seconds! Have I finally got there? I need to do...

- Wed Dec 30, 2009 3:31 pm UTC
- Forum: Science
- Topic: Motion in a straight line (Physics)
- Replies:
**28** - Views:
**3164**

### Re: Motion in a straight line (Physics)

I think the problem here is that I know how to integrate and differentiate, but only by rules. I don't think I actually understand what I'm doing with this in the context of motion in a straight line. I can't see how I'd work out the time it takes for the projectile to hit the ground with the equati...

- Wed Dec 30, 2009 4:06 am UTC
- Forum: Science
- Topic: Motion in a straight line (Physics)
- Replies:
**28** - Views:
**3164**

### Re: Motion in a straight line (Physics)

Hey guys, I'm sorry I've not been around lately, I've been away over the christmas break and such. I've just recently come back to trying to work out this problem and it's doing my head in! So I integrate the acceleration, find v(t) and plug in the time for initial velocity 30ms^-1 as being 0, which...

- Tue Dec 22, 2009 10:12 pm UTC
- Forum: Science
- Topic: Motion in a straight line (Physics)
- Replies:
**28** - Views:
**3164**

### Re: Motion in a straight line (Physics)

Oh I see, I didn't know I could use constants, neat. So I integrated a(t) = -9.81 , and got v(t) = -9.81t + C The problem I have here is that I'm not sure what to do next. I thought to put the velocity in as the C value, 30, is this the right thing to do? From here I integrated again...

- Tue Dec 22, 2009 1:08 pm UTC
- Forum: Science
- Topic: Motion in a straight line (Physics)
- Replies:
**28** - Views:
**3164**

### Re: Motion in a straight line (Physics)

okay, I spent a good 20 minutes on this problem, and I can't manage to work out where to start (which seems to be a problem i often have with math). Gravitational acceleration is -9.81ms^{-2}. If you toss something straight up at 30ms from a point 40m above the ground, how long will it take to hit t...

- Tue Dec 22, 2009 12:08 pm UTC
- Forum: Science
- Topic: Motion in a straight line (Physics)
- Replies:
**28** - Views:
**3164**

### Re: Motion in a straight line (Physics)

Wonderful. Thank you very much, jaap, I really appreciate it! I have another problem similar to this one, but I'll try and work it out myself before I put it in here.

- Tue Dec 22, 2009 12:04 pm UTC
- Forum: Science
- Topic: Can lead be turned into gold?
- Replies:
**20** - Views:
**3514**

### Re: Can lead be turned into gold?

It could be done via nuclear fission I believe.. but the resulting gold atom would be radioactive and extremely unstable. I don't think it would be around for very long before breaking down into a different isotope or atom.

- Tue Dec 22, 2009 9:08 am UTC
- Forum: Science
- Topic: Motion in a straight line (Physics)
- Replies:
**28** - Views:
**3164**

### Re: Motion in a straight line (Physics)

Rad! So to find the displacement I need to integrate our function v(t) = (2/3)t^3. This gives s(t) = (1/6)t^4 + C if s(0) , then C = 0 so after 5 seconds, s(5) = (1/6)(5^4) + 0 = 104.17m and it's velocty at v(5) = 83.34ms^{-1} Is this all corre...

- Tue Dec 22, 2009 8:24 am UTC
- Forum: Science
- Topic: Motion in a straight line (Physics)
- Replies:
**28** - Views:
**3164**

### Re: Motion in a straight line (Physics)

Okay I'm having a little bit of trouble keeping up here, so tomorrow I think I'll start refreshing myself on integration. I have done this sort of problem, but a long time ago, and unfortunately the person who lent me their lectures didn't take notes for this question. So, Jaap, this is a simple alg...

- Mon Dec 21, 2009 2:59 pm UTC
- Forum: Science
- Topic: Motion in a straight line (Physics)
- Replies:
**28** - Views:
**3164**

### Re: Motion in a straight line (Physics)

I sort of understand what you all mean with the definite integral. from the definite integral I got the result 83.34 + v 0 . Is this right? Where would I go from here? v(t) = 83.34 + v 0 how so I work out the value for v 0 ? Wait, I'm supposed to still have a t in here somewhere aren't i.. H...

- Mon Dec 21, 2009 1:57 pm UTC
- Forum: Mathematics
- Topic: Need help with basic trigonometry, namely identities
- Replies:
**7** - Views:
**1387**

### Re: Need help with basic trigonometry, namely identities

hey thanks, you guys, that all really did clear things up. I know how to approach the problem now, just wasn't sure if my way was right. I'm slowly becoming more familiar with all the trig functions!

The clarification on the reciprocals and their ordering was especially helpful too!

The clarification on the reciprocals and their ordering was especially helpful too!

- Mon Dec 21, 2009 1:46 pm UTC
- Forum: Science
- Topic: Motion in a straight line (Physics)
- Replies:
**28** - Views:
**3164**

### Motion in a straight line (Physics)

I'm currently learning motion in a straight line, through use of differentiation and integration. I've sort of understood the concept, I also did it in math last semester, but I can't see where to start with this problem. For starters, here's the problem: A car starts from rest and accelerates at 2t...

- Sat Dec 19, 2009 3:16 pm UTC
- Forum: Mathematics
- Topic: Need help with basic trigonometry, namely identities
- Replies:
**7** - Views:
**1387**

### Need help with basic trigonometry, namely identities

So I'm going through some introductory trig notes, and I understand when to use sin , cos , tan and that their inverses are sec , csc and cot . I understand the pythagorean identities, namely sin^2x + cos^2x = 1 , (x being theta), and I know how to derive the other two laws by dividing by cos and th...

- Wed Dec 16, 2009 9:05 pm UTC
- Forum: Mathematics
- Topic: Introduction + A few simple questions
- Replies:
**15** - Views:
**1796**

### Re: Introduction + A few simple questions

Ohhh okay I've sorted that out then, that all makes sense! So how come one would go about using that formula rather then the simple [imath](u'v-v'u)/v^2[/imath]?

Is it because you guys just derive it yourself from another formula which makes more sense to you just from experience with the subject?

Is it because you guys just derive it yourself from another formula which makes more sense to you just from experience with the subject?

- Wed Dec 16, 2009 9:04 pm UTC
- Forum: Mathematics
- Topic: Mathematicians and String Theory/M-Theory
- Replies:
**6** - Views:
**1801**

### Re: Mathematicians and String Theory/M-Theory

Neat, how interesting. Thanks for the information, guys.