 # Janus

Resident Experts

2039

26

## Everything posted by Janus

1. ## How long till the sun goes supernova?

2. To add to what Swansont has already stated. The speed of light in a vacuum is always c, where c is 299,792,458 meters/sec as measured by any observer. Thus say you have three observes: A; standing next to the light source, B; moving away from the light source, and C; moving towards the light source. Each has a device capable of measuring the speed of the light from the source relative to themselves. They will each measure that the light has a velocity of c to relative to themselves.
3. It depends on your orientation of the ship's gravity to the impact. If the impact is at a right angle to the "up" of your ship's gravity and strong enough, then, yes, you will be thrown off your feet. While the gravity will pull you down to the deck plates, it has no sidewise component. If the ship is hit hard enough to shift it sideways, your feet, due to the friction between them and the deck plate, will go with it. your upper body, however will try and stay in place (law of inertia). Your feet come out from under your center of gravity and you lose balance. If you were hit from the "bottom", you would feel heavier for a moment. If the impact is large enough and you weren't prepared, you could also end up falling. If you were hit from the top, you would feel lighter, and again, depending on the severity of the impact and what you were doing at the time, it could throw off your balance.
4. ## Validity of non-carbon based life

While there has been some speculation on the possibilty of silicon based life, I don't think that any positive conclusion of it possibility has been reached. In fact, most of the evidence points against it. Example: carbon dioxide is a gas at standard temp and pressure, silicon dioxide is a solid. The same is true for other silicon based molecules. This means that silicon based molecules tend to be less reactive. In order to form life you need chemical reaction to take place. A way around this is to place the molecules in a warmer enviroment, meaning you would need a hot planet for silicon life. The problem is that you also need complex molecules for life, and molecules made from silicon chains are more fragile than those made from carbon. The upshot is that the conditions needed for the molecules to be reactive enough for silicon based life to exist are too harsh to allow the formation of the complex molecules needed for life.
5. The trick to all this is the rocket equation. v_f = v_ex ln( M_i/M_f) The part within the parenthesis is known as the mass ratio, and is the ratio of the fully fueled rocket to the rocker empty of fuel. for any given mass ratio, the final velocity of the rocket depends on the exhaust velocity. the higher the exhaust velocity the greater final speed your rocket can achieve with the same amount of fuel. In other words, higher exhaust velocity leads to better efficiency. The ion rocket is more efficient that the chemcal rocket because it is capable of producing higher exhaust velocity. The downside is that Ion drives produce a "thin" exhaust (The total amount of exhaust it can produce in a given amount of time is low), this leads to low thrust and slow acceleration. Falling somewhere between is a system under development called a VASIMR (VArible Specific Impulse Magnetohydrodynamic Rocket) It is more efficient than chemical rockets, while producing more thrust than ion rockets. It is also adjustable so that you can choose either the highest efficiency or the most thrust, depending on the what you need at the moment.
6. Well, Proxima (Alpha Centauri C) is the closest star, but it is unknown as to whether is has any planets. It is a small red dwarf that is part of the Alpha Centauri system which also includes Alpha Centauri A & B. 'A' is a yellow star of about the same mass as the sun, and could have planets in the habital zone, but it is unknown as to whether it does.
7. http://web.mit.edu/space/www/voyager/voyager.html
8. ## Basic Relativity Question

9. ## Is there a way to find out the current Earth-sun distance?

Go to http://ssd.jpl.nasa.gov/cgi-bin/eph Choose the target as the Sun. Set the date/time range you want. Generate the ephemerides. The distance to the sun will be under the heading "delta" and in AU. One AU is 149,598,550,000 meters.
10. A graviton would be a quantum of gravitational raditation, in the same way that a photon is a quantum of electromagnetic radiation. And just like the virtual photon is the mediator for the electromagnetic force, it is the virtual graviton that would mediate gravity. This is assuming that gravity can be quantisized.
11. Its me, I forgot to convert the meter/sec to cm/sec before plugging the numbers in. It would be 125 watt-sec, .03 watt-hrs, run a 100w bulb for 1.25 secs, etc.
12. No, Mass x velocity is momentum. The force imparted in an impact is related to the "stopping" distance of that impact, which in turn is related to the stopping time, and that in turn is a measure of acceleration. I.E. It takes ten times more force to stop a bullet over a distance of 1 mm then it does to stop it over 1 cm. Of course it takes the same energy to stop the same bullet in both instances, as energy is force times distance.
13. As stated above, the speed of sound in a gas is: $v= \sqrt{\gamma R T}$ Gamma is the Ratio of specific heats R in the gas constant T is the Temp in Kelvin. For air: Gamma = 1.4 R = 286 For CO2: Gamma = 1.3 R= 189 From this it is obvious that sound travels faster in air. (330 m/s vs 259 m/s at 0 degrees C)
14. ## Acceleration of Gravity for large objects

Yes, they do. Your calculations only took into account the acceleration of M1 due to its attraction to M2, but neglected the acceleration of M2 due it's attraction to M1.
15. ## Is the Universe travelling or the Space Ship ?

If the twin accelerates then S' is not an inertial reference frame and remain permanently attached to the twin. If it is an inertial refernce frame it cannot remained attached to twin. Now, the formula above does not involve the acceleration a of the ship, it only makes reference to the instantaneous relative speed v. So if you look at things from the point of view of the twin in frame S`, he sees his brother accelerate away from him at speed v as well. No, he can easily tell that he was the one who actually accelerated. He can feel the acceleration, he can fire a laser perpendicular to his path and notes that it curves, etc. And while the time dilation formula holds when used by either twin while they are at constant velocity, and holds for the twin that does not accelerate (remains in the same reference frame the whole time.), It is incomplete for the twin who undergoes acceleration while he is accelerating. For him he has to add an additional transformation that takes into account his acceleration and the distance between himself and his brother. No paradox as long as you take all the consequences of Relativity into account, including length contraction and Relativity of simulataneity. No, it is not. Again you must take all the effects involved into account to properly address this. In fact, when you do take them into account, the time dilation formula must be applied in [/i]all[/i] frames in order for there not to be a paradox. I would strongly urge you not to try and explain Relativity to others, you do not grasp it properly yourself.
16. ## earth and moon proportionality

No, that remark was not correct. Let's see if we can make things clearer. The force acting between two bodies is equal to the formula given already: $F= \frac{GMm}{d²}$ G is the universal gravitational constant. M is the mass of one body and m the mass of the other d is the distance between their centers. Using this we can calculate the force between the Earth and a 1kg mass sitting on its surface: The radius of the Earth is 6,378,000 m so this is d The mass of the Earth is 6 x 10^24 kg so we get: F= $F = \frac{((6.673 x 10-11)(1)(6 x 10^{24})}{6,378,000^2}=9.8N$ For the Moon, Mass = 7.35 x 10^23kg radius = 1,735,000m So the force acting on the same 1kg weight sitting on the Moon is: F= $F = \frac{((6.673 x 10-11)(1)(7.35 x 10^{22})}{1,735,000^2}=1.6N$ 1/6th that of if it was sitting on the Surface of the Earth. So we can see that even though the mass of the Moon is only 1/81 that of the Earth, an object sitting on the Moon's surface is is less than 1/3 as far from the Moon's center than an object sitting on the surface of the earth is from the Earth's center is. This is why the force of gravity on the surface of the Moon is 1/6 that of that on the surface of the Earth.
17. ## Question about General Relativity Theory

That's like asking: If Unicorns really existed, would their horns actually be an aphrodisiac?
18. 19. ## Will a Magnetic Induction Engine work?

Yes.
20. A magnet is a magnet because of two things: 1. the indivdual atoms/molecules have a magnetic moment(due to an imbalance of the spins of the electrons each atom has a net magnetic field. 2. These moments are aligned. (the magnetic fields of the atom all point in the same direction.) And thus re-enforce each other. If you strike a magnet sharply, you "dislodge" some of these atoms out of alignment and randomize them so that they no longer add to, and to some extent cancel out the total field of the magnet. The same thing happens if you heat a magnet. As you heat it, the atoms vibrate. Heat it enough and the atoms will vibrate right out of alignment, and you will demagnetize your magnet.
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