## Search found 14 matches

Sun Dec 11, 2011 4:11 pm UTC
Forum: General
Topic: You are the last person left on earth. What do you do?
Replies: 256
Views: 46671

### Re: You are the last person left on earth. What do you do?

What strikes me about this thread is the huge number of people that want to "learn to fly an airplane from a book".

The future of humanity relies on a guy that's probably going to kill himself 10 minutes after finding the nearest airfield.
Sat Sep 24, 2011 1:39 am UTC
Topic: 0955: "Neutrinos"
Replies: 159
Views: 44298

### Re: 0955: "Neutrinos"

I am a first year undergrad physicist, and so my knowledge of particle physics is fairly rudimentary.

Are neutrinos more or less weakly interacting than photons?
That is, is it possible that neutrinos interact with an imperfect vacuum less than photons do, explaining the minor speed difference?
Fri Apr 22, 2011 4:23 am UTC
Topic: 0889: "Turtles"
Replies: 207
Views: 60009

### Re: 0889: Turtles

Are turtles self aware?
Sat Nov 13, 2010 10:37 pm UTC
Forum: Mathematics
Topic: Inverse matrices and the determinant
Replies: 4
Views: 3172

### Re: Inverse matrices and the determinant

Thank you guys.

I have figured that (I+A)(I-A) = I^2 - A^2 = I
so the inverse of (I-A) in the A^2 = 0 case is (I+A)

similarly in the A^3 case (I+A+A^2)(I-A) = I

so the inverse is the geometric series 1 + A + A^2 + ... + A^(n-1)
Sat Nov 13, 2010 9:56 pm UTC
Forum: Mathematics
Topic: Inverse matrices and the determinant
Replies: 4
Views: 3172

### Inverse matrices and the determinant

This is homework, I'll post what I've done so far. Let A be a square matrix. Given A^2 = 0, show that (I-A) is invertible. (then extend this to A^n) I can see that if A^n = 0 then det(A) must be zero (as det0 = 0) and so A isn't invertible. How can I go from here to showing that det(I-A) is nonzero?...
Thu Apr 08, 2010 9:48 pm UTC
Forum: Science
Topic: Humans born on Mars
Replies: 58
Views: 5294

### Re: Humans born on Mars

Do you mean ~0.38g?

edit: Hahaha, it's a tilde when I type it, the board converts to a dash. What the hell?
Thu Apr 08, 2010 3:25 am UTC
Forum: Science
Topic: A physics question.
Replies: 7
Views: 1001

### Re: A physics question.

I am too lazy to make a diagram right now, but as a thought exercise, you're walking up a hill. The hill in this sense is your "plane". When it's at zero degrees, gravity's force is completely perpendicular to the plane, 9.81m/s^2. As the hill gets steeper, you're still walking on the plan...
Sun Apr 04, 2010 11:16 am UTC
Forum: Science
Topic: Why does c =c ?
Replies: 32
Views: 4217

### Re: Why does c =c ?

thoughtfully wrote:The clearest way of seeing c as a maximum speed is to see it as the only speed (in all four dimensions of spacetime)

Wow. I love physics.
Fri Apr 02, 2010 6:33 pm UTC
Forum: Science
Topic: Why does c =c ?
Replies: 32
Views: 4217

### Re: Why does c =c ?

Light doesn't "accelerate". It always travels at c. Even in a refractive medium, photons themselves travel at c before being absorbed/reemitted (the act of which slows them down). I believe that certain properties of vacuum prevent light from traveling faster/slower than it does, I'm only ...
Tue Mar 30, 2010 1:47 am UTC
Forum: Mathematics
Topic: Changing complex coordinates to trigonometric form.
Replies: 5
Views: 971

### Re: Changing complex coordinates to trigonometric form.

skeptical scientist is of course correct, however I always found that this was easier thinking geometrically. You can see from the diagram theta is 180deg + the angle in the triangle. Now just take the triangle, adjacent side is (3/2), hypotenuse 3, the ratio adj/hyp is 1/2. 1/2 is of course cos60 f...
Sat Feb 13, 2010 1:41 am UTC
Forum: Science
Topic: Regression of Cooked State into an Uncooked State
Replies: 37
Views: 8727

### Re: Regression of Cooked State into an Uncooked State

A simpler thought experiment is "unbreaking a ming vase". You have a ming vase on the edge of a table. It falls off, shattering on the ground. Imagine if all of the parts of the ming vase exactly reversed their direction. They would have enough energy to fly together, recrystallise the br...
Fri Nov 20, 2009 4:26 pm UTC
Forum: Science
Topic: The energy efficiency of boiling cold vs hot tap water.
Replies: 30
Views: 3258

### Re: The energy efficiency of boiling cold vs hot tap water.

I would imagine the boiler has a far easier job heating the water due to insulation.
Sun Nov 01, 2009 12:06 pm UTC
Forum: Science
Topic: Physics Question
Replies: 9
Views: 1582

### Re: Physics Question

Yeah, in that situation you could just turn the rockets off for .0000000000000001 seconds and just treat it as if you never even stopped...
Sun Oct 18, 2009 8:55 pm UTC
Forum: Mathematics
Topic: Circles and squares
Replies: 1
Views: 495

### Circles and squares

Hello, this is my first post on the xkcd boards :) My problem is such (not so much homework but just something I am reading into) http://i108.photobucket.com/albums/n39/mredgey/circles.png I need to find the length of "x" (in terms of r). The way I am approaching it is to use the right ang...