# MrMongoose

Senior Members

216

1. ## Harmonic Dark Matter

Aren't ions in crystals of normal matter continuously vibrating anyway?
2. ## An impossible brain teaser

[hide]N A B C D E F T[/hide]
3. ## Projection of a helix to 2d?

I assumed he meant parallel, but as for the cycloid... Why? I'm not sure here, but from observing my trusty spring, it looks as if thats just the general case for the projection onto any plane, and just as the circle is one extreme, for this other extreme, we can specifically say its sinusoidal.
4. ## Shooting down satellites?

I understand why people are concerned, but it seems as ridiculous as not developing a chemical which could potentially kill cancer because it could potentially be used to kill Chinamen.
5. ## Shooting down satellites?

What has this got to do with militarisation? I didn't realise that it's an act of war to dissemble your own equipment.
6. ## Projection of a helix to 2d?

It should just be a sinusoid. If you imagine a plane with the helix axis normal to it being moved along the helix, the intersection of the helix and the plane will move around in a circle at a constant rate. The distance of the intersection from the axis of the helix is constant, but the displacement expressed as as two orthogonla vector components, i.e. projections onto two orthogonal planes will be two orthogonal sinusoids. You can pick any plane and the projection will be a sinusoid with the phase depending on the plane chosen.
7. ## Word Puzzle

Table? Where?
8. ## Series of basic questions on microscopes

It says image, not specimen. I'd say the obvious answer is that it shows things how they really are. Most people assume that a microscope shows things the right way round.
9. ## Walking in Circles

There will certainly will be coriolis forces- one from the rotation of the Earth about its own axis and another from the rotation of the Earth about the centre of its orbit, though they will be negligible compared to the other effects mentioned. The rotation of the earth will also have an effect on the climate, and wind patterns have an effect of surface soil formations which may cause slight gradients in certain directions. Though, these will cause gravitational components along the ground in predetermined directions rather than in the centripetal direction. Also, as the Earth spins and day becomes night, wolves come out and will chase you in a direction you hadn't planned on heading in!
10. ## Prove it!

Also, are you familiar with the word please?
11. ## Third Eye or Inner Eye

This is a brain teaser?
12. ## Optimization Problem

I wish my job was that easy!
13. ## hole in a cylinder

The point is that it isn't a 6" cylinder projected through a sphere and the overlap discarded. It is a 6 inch deep cylindrical hole in the sphere, so it MUST pass through the centre and its ends must be on the surface of the cylinder. What I think should have been added to the original question, however, is that the hole goes through the sphere from one surface to another. I just assumed that that was what was meant as there was apparently a unique solution.
14. ## hole in a cylinder

Can't argue with the third one so I'll go about fixing it, and I agree the first thing is a bit shoddy. As for the second, I said they move closer in terms of angle, i.e. the cylinders length increases with respect to its radius. Again perhaps I should have been clearer! Might as well get your moneys worth;)
15. ## hole in a cylinder

I think this is right... I take it that if the hole is 6 inches deep and goes all the way through, then there are a limited set of solutions- one for each sphere. As the sphere gets larger, the edges of he whole move nearer (in terms of angle not necessarily size) to each other. If we take a calculus based approach here, a sphere of radius r is made up of a series of infinitessimal disks, but when the cylindrical hole is drilled, it becomes a series of infinitessimal annuli. moving upwards from the "equator" with h increasing , the radius, y, of any one disk is given by $y=(r^2 -h^2)^\frac{1}{2}$ Taking a cylindrical hole of radius x out with the cross section of the cylinder to what I previously called the "equator", the width on an annulus w is, $w=(r^2 -h^2)^\frac{1}{2} -x$ And when the value of h is equal to 3 (i.e. the limit of a 6 inch hole, half being each side of the equator) the width of the annulus is 0, thus, $0=(r^2 -3^2)^\frac{1}{2} -x$ Which gives $x=(r^2 -9)^\frac{1}{2}$ And the volume of an annular element is thus given by $\frac{dV}{dh}=\pi((r^2 -h^2)^\frac{1}{2})^2-\pi((r^2 -9)^\frac{1}{2})^2$ $\frac{dV}{dh}=\pi(r^2 -h^2-r^2 +9)$ $\frac{dV}{dh}=\pi(9 -h^2)$ Summing for the hole depth of 6 inches, $V=\pi\int_{-3}^{3}(9 -h^2)dh$ $V=\pi[9h-\frac{h^3}{3}]^3_-3$ $V=\pi(27-9)-\pi(-27+9)=36\pi inches^3$
16. ## Salt and Water

Of course it works. When they grit the roads, thats mainly salt.
17. ## The Cost of (Iraq) War

You have to spend money to make money. Just to be clear, the greatest negative gradient on the graph is immediately after a war Me donating solar panels to my landlord is about as realistic as 2.4 trillion dollars even existing if it weren't for war.
18. ## The Cost of (Iraq) War

Beacuse war is the only option that will make a profit So why does he only say he wouldn't do this one? If he didnt want to do the others, he'd say the same for everything. You misunderstand. I said I do as much as I can considering don't own my own house. My landlord wont let me tear the roof down and cover it in solar panels.
19. ## The Cost of (Iraq) War

I stand corrected. And yes... thats about right. The guy was just too desperate to show that he didnt want to make rich americans comfier, but rather to help foreigners. I'm not entirely comfortable with war, but realistically, the video is a load of crap. On the contrary, I realise that carbon dioxide is not so inevitable and that I personally can make a change, so do the best I can in my current situation (not owning my own house as I do).
20. ## Cryptogram Assistance ...

HAHA a=h b=i e=l f=m g=n h=o i=p k=r l=s m=t n=u p=w q=x r=y t=a u=b v=c w=d x=e y=f z=g YOU ARE SO YUMMY I COULD EAT YOU UP WHAT ARE YOU DOING NEXT FRIDAY I WILL BRING THE OIL AND THE CANDLES Have fun on friday;)
21. ## perpetual motion [quick question]

How can something be perpetual to a point?
22. ## The Cost of (Iraq) War

Glad someone isn't completely brainwashed. I think the "Not that I think we should do it, just that we could" was just put in to show contempt for laptops because they don't save trees and whales and baby jesus.
23. ## The Cost of (Iraq) War

Well if accurate information is effective propoganda, then it is propoganda. So saying it's not propoganda because it's accurate makes very little sense. I don't see why people need to be told what to think about.. like sheep.
24. ## Conservation of enthalpy

Adiabatic and reversible together imply isenthalpic, so it might help to ask yourself how steady flow is connected to those two.
25. ## Need help wrapping Christmas present for next year (2008)…

That's just so cool that I have to ask what you send when its not your turn with the flag!
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