# Search results

1. ### Finite Cylinder in an electric field

Hi, I was just wondering if anyone could might know where maybe the following situation has been worked out: A finite cylinder of length L sticks out of a flat, horizontal plane. The plane and the finite cylinder are both grounded, and are placed into a previously uniform electric field, E =...
2. ### Electron / muon

Well, since you mentioned Muons, I figured I'd bring up: http://en.wikipedia.org/wiki/Muon-catalyzed_fusion Of course, it is impractical, and would be foolish to develop as an energy source, but still kinda neat.
3. ### What are projects about nuclear controlled fusion reactor to achieve Q > 1

Here's a few links about the performance of JT-60 if you're interested. I guess they were able to reach gains of 1.25 or thereabouts. http://www.mext.go.jp/english/news/1998/06/980611.htm [Broken] http://www.jaeri.go.jp/english/press/980625-jt/ [Broken]
4. ### Interesting story

Ah ok, you mean like making the semiconductor devices themselves and things like that... Yeah that's not happening, heh.
5. ### Interesting story

Just some guy who built his own playstation 2 portable - as in it can play playstation 2 discs (and also playstation 1 games) in a handheld console.
6. ### Interesting story

Hey Pengwuino, have you seen this guy? http://www.benheck.com/
7. ### Mathematicians and physicist underpaid

Hmm... I wonder if my physics degree will help me break into the garbage picking industry...
8. ### Measuring the height of a building

What's wrong with using a barometer? Are you not allowed? Your second idea sounds pretty good, where you drop an object and listen for it to hit the ground, seems like it would be quicker than trying to measure shadows and figure out angles.
9. ### Bijection, Injection, and Surjection

So would a bijective homomorphism be an isomorphism? I was taught (working with vector spaces) that a linear bijection is an isomorphism. Are these okay?

I once saw a 6x1.5 inch cylindrical magnet on ebay, i think around 200 hundred dollars? If I had an extra two hundred dollars, and perhaps an application for it I'd like to get one of those. I guess the optimal geometry for the neodymium magnet is a 1/8 "pancake" or cylindrical height/diameter...
11. ### Motorcycle Crash

425 pounds ---> about 200 kg, if we add the driver that's about 290 kg, 155 mph ---> about 70 m/s, so the kinetic energy is 1/2 mv^2 ---> ~ 95,550 joules. What units do you want? Joules? Calories? Btu's? Kilowatt-hours?

What kind of application? I would recommend looking into magnets of the neodyium iron boron variety. Just search for them on ebay, you should see a lot for sale there. I bought a 2x2x1 inch neodyium magnet that i think lifts over 200 pounds of steel. I've tested a little under 200 pounds so...
13. ### Accelerators and fusion of elements

Huh, nifty. I wonder what the cross section for neutron capture of Hg 196 would be?
14. ### Quantum Entanglement and Communication

So, in essence, I'd have to call you up and ask you about your data you have on betelgeuze which would basically defeat the point of using this method to communicate, right?
15. ### Evaluate the following integral

If you want to skip the integration by parts, you can choose to use the differentiation under the integral sign: \int_{-\infty}^{\infty} x^{n} dx e^{-ax^{2}} = \int_{-\infty}^{\infty} dx \frac{d^{\frac{n}{2}}}{da^{\frac{n}{2}}}(-1)^{\frac{n}{2}}e^{-ax^{2}} So now you can take the...
16. ### A tricky integral

Did you mean this? E(\phi , k) = \int_{0}^{\phi} dt \sqrt{1 - k^{2} \sin^{2}{t}} An elliptic integral of the second kind?
17. ### Lagrange and Hamiltonian question

Additionally, you may want to write the derivative with respect to time in the final differential equation (containing r's and theta's) as: \frac{d}{dt} = \frac{d\theta}{dt} \cdot \frac{d}{d\theta} Nothing more than a chain rule here. However, you're probably going to glean a lot of...
18. ### Lagrange and Hamiltonian question

Well, I guess the easiest way to go about figuring it out would be to start out by writing the lagrangian, but in polar cooridinates (kinetic energy, potential energy parameterized by radius, theta). Once you have done this, you should be able to see where it goes. Of course you could also...
19. ### Infinite sum

I don't know if this is really adding to the discussion or not, but if you perform the integral test on the (harmonic) series, (using a as any constant, doesn't matter), you end up with \int^{\infty}_{a} dx \frac{1}{x} when integrated gives \ln{x}|^{\infty}_{a} = \ln{\infty} - \ln{a}...
20. ### What's your favorite tea

Favorite teas? Well, for me personally I would say: 1.) Earl grey 2.) Chai 3.) English Breakfast 4.) Orange pekoke 5.) green tea 6.) Chamomile (although I usually reserve this for when I have a sore throat or am sick, it is quite soothing) And that's all I can think of right now
21. ### Infinite sum

Yeah weird to think about I guess, but \sum^{\infty}_{i =1} \frac{1}{i} is a divergent series, so it has to be true. Seems that it is not something easy to think about intuitively
22. ### Mathematica Fundamental rules for physics mathematical derivations.?

As was mentioned before, there is not necessarily one simple set of rules to follow in order to tackle a physical problem. What works the best in learning how to solve physics problems is actually doing them, that is, practice. It's something you have to do in order to really learn.
23. ### A shorter proof to 0.999 = 1

Does anyone have any links to the original discussion from battle.net? Thanks in advance.
24. ### Prove that the limit of the functions

Note that e^{ix} is bounded: e^{ix} = \cos(x) + i\sin(x) so, for large, or arbitrary x, e^{ix}, the imaginary part will never be greater than 1, and the real part will never be greater than 1. Thus, if you had: \lim_{x \rightarrow \infty} e^{(i-1)x} the e^{-x} part forces the whole...
25. ### Righty tighty, lefty loosy

Another example of left-handed threads can be seen in scythes (the thing that death carries around). Since it is swung from right to left, the grips on the handle would have a tendency to loosen if a right-handed thread were used. Screws remind me of cross-products as well
26. ### Computers & Determinants

Looks like if you pick out all the distinct terms (the ones in the summation that aren't equal to zero) you get (N!). On top of that, you would need to do N multiplications each time (so N multiplications N! times). Yikes Yeah didn't work that one out before
27. ### Govt Poisoning us through Water supply?

A very awesome movie was (sort of) based on the danger of flourine in our water: http://www.imdb.com/title/tt0057012/ Although I suppose this has no relevance to the discussion.
28. ### A car question

first and second gear on an automatic are for "pulling stumps out of the ground".
29. ### Computers & Determinants

How would this fare computationally? det(A) = \sum_{{i}_1, {i}_2,...,{i}_n = 1}^{N} \epsilon_{{i}_1, {i}_2,...,{i}_n} a_{{i}_1, 1} \cdot a_{{i}_2, 2} \cdot \cdot \cdot a_{{i}_n, N} Cumbersome and inefficient for a computer algorithm?
30. ### PETA activist group or whacko brainwashing cult?

Darn. You beat me to it. That was the first thing I thought of when I saw this thread.