Greg H.

My avatar is the photo negative of a false color image of the magnetic field lines of a black hole. In the context of this thread, my post makes as much sense as the OP.

If its kinetic energy stayed the same, I would expect its momentum to change, since a comet will lose mass as it passes the sun due to out-gassing. The change in momentum would be required to maintain the same [math]E_k[/math]. That doesn't make your statement about the ball any less ludicrous as the math simply doesn't support your statement. You cannot change the momentum of the ball without the mass also changing, and have [math]E_{ki} = E_{kf}[/math]. They're called equations for a reason - they have to be equal.

What you just stated is a physical impossibility unless the ball somehow gained mass by bouncing off a wall it passed none of its kinetic energy to.

Changes in momentum cause changes in kinetic energy by: [math]E_k = \frac{p^2}{2m}[/math] where p is momentum m is mass of the body.

It's not that they can't, it's that they don't. Do some reading on the electron cloud model.

No, they really aren't, when you get right down to it. They're a lot better than they used to be, but you can still kill one with a stray burst of radiation. They're delicate, finicky, and it's only thanks to governing standards that they can even talk to one another at all. You want resilience, use an abacus, a pencil, and a scrap piece of paper.

Job trading only works within a narrowly defined field, which is not what I think you're discussing. I doubt anyone wants their greengrocer and their neurosurgeon to trade places the day they're due for brain surgery.

Releasing a virus like that would kill a lot more people than you might expect. Ask yourself this - if 5 billion people all dropped dead within, say, 10 days of one another, how are the other billion supposed to dispose of the bodies without the decay polluting the ground and water. Sounds like a good recipe for sickness and (additional) death to me.

So given the choice between "My multimeter is on the fritz" and "The laws of physics are wrong" you went with the second one. That pretty much tells us all we need to know.

As Enthalpy says, it's the density that matters. You can actually calculate surface gravity based on density using the following: [math]g = \frac{4\pi}{3} Gpr[/math] Where [math]p[/math] is the density of the object at radius [math]r[/math]. Since [math] p = \frac{mass}{volume} [/math] you can compute the change in the surface gravity based on the changes in volume and mass of the planet as compared to earth.

Use [math]g = \frac{-GM}{r^2}[/math] to calculate the surface gravity of the planet you care about. Then just compare that to Earth Norm (~[math]9.8 m/s^2[/math]) Edit: Had to remind myself how to do Latex. Been gone a while. Edit 2: Looking at your numbers, the 40kg seems right, if I'm doing the math right (albeit, I'm doing it in my head, so I may be off by any number of orders of magnitude). Edit 3: Actually, kg is a measure of mass, not weight, and your mass wouldn't change. Your weight (in Newtons) would change by 1/2. On Earth, you weigh [math] 80 kg \times 9.81 m/s^2 = 784.8 Newtons[/math]. On a planet twice the mass & twice the radius of Earth, you should weigh 392.4 Newtons.

The issue is that, there are actually two air brake systems on most modern North American trains. You have the individual reservoir on the car which is what actually provides the clamping power for the brakes. By default, this tank holds the brake closed by supplying constant pressure from what's called the train line. A separate line, called the brake line, uses compressed air supplied by the locomotive to engage and disengage these tanks, which is what releases or applies the brakes. The problem is that the locomotive is also responsible for keeping the air brake reservoirs on each car fully charged (via the train line). If a car needs to sit for a long period of time without a powered locomotive, manual hand brakes still need to be set (they're the large wheels you see on the ends or sides of the railway cars). Without a running locomotive, eventually the charged air system will leak away enough pressure that it can't hold the brakes closed. If the manual brakes have not been engaged at that point, the whole thing is basically at the mercy of gravity and friction. If you're interested, here's a recent article from popular mechanics that explains it in more detail without being too technical. http://www.popularmechanics.com/technology/engineering/understanding-a-runaway-train-how-do-air-brakes-work-15678938

That's the best thing about science, to be honest - it's self correcting. If you somehow manage to publish a paper that's full of bunk, someone, at some point, will try and recreate it and point out the flaws in your work. It may take a while (like the whole sun orbits the Earth thing), but eventually science fixes its mistakes.

It would depend entirely on how their brain was wired and what happened to the electrical signals the brain captured in response. "Seeing" is just a convenient term to used to describe one possible method of processing external spatial stimuli by the brain. There's no reason to say that bats cannot "see" using echolocation, and indeed, judging by the size of the objects they routinely hunt, their "vision" has a much finer resolution than ours, at least at close range. However, given that bats operate in a three dimensional environment as a matter of course (being flying mammals), their brains certainly have the capability to represent their environment topographically to keep them from flying into things. Is that good enough to be called "seeing"? THat's probably for the philosophers to decide. 1: http://www.neuro.uoregon.edu/wehr/lecturenotes/echolocation%20lecture%20notes.pdf, p 4

As this is a homework assignment, I won't provide you with the the answer directly. What I will say is take a look at the methods in the Java.Math class. Some of them may be what you need.

I was going to suggest this. I've read the book twice myself, and it's actually quite interesting, especially in the time differences between the humans and the cheela (the aliens on the neutron star). Well worth the read. Forward also included some appendixes (at least in my copy) that delve more into the science behind the book.

To put that another way - maybe the problem is they're just aggravating twits, rather than their political leanings.

Threads like this make me ask why we can only give out 1 neg rep a day. Can I have a few more just for the next 24 hours?

I'm just going to leave this here. http://mythbustersresults.com/nasa-moon-landing Enjoy.

Perpetual motion supporters are the snake oil salesmen of the modern era. If you simply assumed that everything they say is deliberately deceptive, you wouldn't be far off the mark.

As a self described control freak, I prefer a manual transmission because it gives me a much better feel for what the car is doing. Between the steering wheel, the pedal under my foot, and the shifter, I can tell when we're about to have a problem early enough to stop it from becoming a problem. it provides you finer control of the car, and it also allows you to adjust the amount of torque you're applying at any given time (for example, for driving on ice or snow - living in Iowa in the winter this is an issue). Manual's are simpler, in concept, since they're just a bunch of spinning gears, as opposed to a fluid based vacuum driven system, I find I get better gas mileage from them, and they are lighter if that's a concern.

For the planet? No. We're incapable of doing any long standing damage on a scale large enough to significantly impact the Earth itself. For every living thing on the planet including ourselves? Yes - as a species we are incredibly arrogant and stupid and seem bent on destroying everything around us as rapidly as possible. Oh, I think my misanthropy is showing.

We have enough trouble just predicting the weather. I shudder to think what might happen if we start actively tampering with it.

But that's just it - we choose what to believe everyday. When a politician makes a campaign promise, I make an active choice to believe or not believe in what he's saying (granted the choice may be easier depending on whether he's spouting bullshit or not). I made an active choice to stop believing in God (or any other deity in general) as a teenager because the more time I spent thinking about tit critically, the more I realized there was no need for it in my life. My belief gradually waned until it ceased to exist.

What do you need it to do, and more importantly, how small and lightweight do you need it to be? I assume, as a DJ you have other pieces of equipment, so the fact that you have to carry something and set it up anyway isn't much of an inconvenience?