Scots Taffer on 31/3/2006 at 06:02
my wife and i once saw a bat masturbate
true story
Wyclef on 31/3/2006 at 06:21
Quote:
let say you are traveling away from the earth at 15,000mph still fast why wouldn't just take a little longer to do it?
This is a really simple but still very instructive concept in energetics. Escape velocity is the velocity one must have at departure from r_0 (the earth's radius) if one isn't expending any additional energy (i.e. through rocket thrust.) 0.5*m_you*v_e^2 = G*m_earth*m_you/r_0; cancel m_you (escape velocity is the same for everyone) and rearrange. At v_escape, one can travel to r = infinity, though at infinity velocity will asymptotically approach zero. Maintaining 15k mph requires a constant expenditure of energy, as the Earth's gravitational potential ~ -1/r.
Just draw out the -1/r potential and everything will become clear. KE_escape = is the distance between the r-axis and the gravitational potential energy at r = r_0.
kingofthenet on 31/3/2006 at 06:36
I am not sure I get that,are you saying it is Possible as long as you have energy to expend? I know Rocket engines tend to work like heating systems in houses, all on or all off,and the longer it is on you ship will contantly be picking up speed,(so it is hard to maintain a steady rate, but the way I understand EV is that if you don't reach that magical speed you can never leave,at all, please advise with less math and fancy words.
Wyclef on 31/3/2006 at 06:48
If you want to escape orbit without expending additional energy -- for instance, without using a rocket -- escape velocity is the velocity you need to have when you leave the surface of the earth. For instance, if you had a sufficiently <A HREF="http://en.wikipedia.org/wiki/Project_Babylon"> powerful gun</a>, you could shoot a bullet that will have enough speed to escape orbit. The bullet's speed will drop as it travels, but it will have just enough energy to escape orbit.
BlackCapedManX on 31/3/2006 at 06:48
Quote Posted by kingofthenet
Agent Monkeesee, you seem knowlegable, answer me this one, what is Escape Volcity, and why is it important, I could never quite grasp it, lets say for shits and giggles, that for the earth it is 25,000 MPH, ok, so not to be really crazy, let say you are traveling away from the earth at 15,000mph still fast why wouldn't just take a little longer to do it? I have heard you would run out of fuel, but that doesn't seem right as it would depend on the "Type" of fuel and engine efficenency,what if you had a hose that supplied endless fuel, couldn't you Escape at like anything over 1mph, so long as you were making "foward" progress.
Presuming you're actually serious about the question (I realize I am not the esteemed Mr. Monkeesee, but you get what you can take):
Engines on any type of vehicle are only capable of a maximum amount of thrust, where the output of energy cannot, via the mechanations of the engine and friction and external forces, actually produce any more total speed. If that initial speed fall beneath the escape velocity, "escaping" cannot happen. This is because velocity isn't constant the way acceleration is constant, at t=0 you may be going 15000 mph but after several seconds your speed would be drastically reduced. The further away from a massive body you are, the slow the rate of this reduction, and the goal is to reach a "safe" distance before that reduction turns into a negative velocity and pulls you back to earth. If your engine is only capable of going 15k mph and you need 25k mph your engine is going to need to be able to get you to 15k mph and another constant +9.8 m/s^2 on top of that, otherwise your 15k is going to turn into 10k and 5k and -5k etc. And if your 15k mph (approx 6700 m/s, since metric is much more convenient) + 9.8 m/s^2 gets you to 25k mph, than you've reached escape velocity and you can leave (it actually work differently than this, since, again, gravity is less the further from earth you go, so if you start at 10000 meters you won't have to keep quite 9.8 m/s^2 since gravity won't be as forceful at that altitude). The issue isn't really escape velocity, it's escape acceleration, the only issue is in the way we can engineer things, and creating a ship with the ability to maintain +9.8 m/s^2 is stupidly hard (in two minutes it would be traveling 3.5x the speed of sound... now realize that this is thousands of tons of metal you're trying to move and the fastest plane we can build goes a little over 2x, weighs much less, and won't get any faster the longer it goes) making it much easier to consider how fast you need somehting to get initially, than how powerful an engine you need to make it maintain escape acceleration. It makes things like ion thrusters and antimatter generators somewhat desirable.
BlackCapedManX on 31/3/2006 at 07:08
Right, but the point is that engines should give continual acceleration, escape velocity only deals with the abstract concept of having a fixed velocity and a fixed gravity at a certain point and knowing what the velocity needs to be move infinitely out of the field. The initial question pertains to why can't you just add more force and keep going, and the answer is basically because we can't practically build the engines to do so.
If we could make a ship that could, regardless of what external forces acted on it, move away from the earth at 2 mph consistantly, it would leave orbit, regardless of what escape velocity says, because velocity isn't the only thing at play here. However, since velocity is the only thing we can practically acheive in great quantities with modern engines, we deal with the term "escape velocity."
I explain it this way rather than with formulas and graphs for the sake of those who don't have sufficient understanding in physics to be able to filter the math through to the logic of it.
Scots Taffer on 31/3/2006 at 07:14
You physics nerds are turning this into a proper discussion.
Bitches, leave.
kingofthenet on 31/3/2006 at 07:14
Quote Posted by BlackCapedManX
Presuming you're actually serious about the question (I realize I am not the esteemed Mr. Monkeesee, but you get what you can take):
Engines on any type of vehicle are only capable of a maximum amount of thrust, where the output of energy cannot, via the mechanations of the engine and friction and external forces, actually produce any more total speed. If that initial speed fall beneath the escape velocity, "escaping" cannot happen. This is because velocity isn't constant the way acceleration is constant, at t=0 you may be going 15000 mph but after several seconds your speed would be drastically reduced. The further away from a massive body you are, the slow the rate of this reduction, and the goal is to reach a "safe" distance before that reduction turns into a negative velocity and pulls you back to earth. If your engine is only capable of going 15k mph and you need 25k mph your engine is going to need to be able to get you to 15k mph and another constant +9.8 m/s^2 on top of that, otherwise your 15k is going to turn into 10k and 5k and -5k etc. And if your 15k mph (approx 6700 m/s, since metric is much more convenient) + 9.8 m/s^2 gets you to 25k mph, than you've reached escape velocity and you can leave (it actually work differently than this, since, again, gravity is less the further from earth you go, so if you start at 10000 meters you won't have to keep quite 9.8 m/s^2 since gravity won't be as forceful at that altitude). The issue isn't really escape velocity, it's escape acceleration, the only issue is in the way we can engineer things, and creating a ship with the ability to maintain +9.8 m/s^2 is stupidly hard (in two minutes it would be traveling 3.5x the speed of sound... now realize that this is thousands of tons of metal you're trying to move and the fastest plane we can build goes a little over 2x, weighs much less, and won't get any faster the longer it goes) making it much easier to consider how fast you need somehting to get initially, than how powerful an engine you need to make it maintain escape acceleration. It makes things like ion thrusters and antimatter generators somewhat desirable.
The thing I don't understand what is slowing you down? Gravity, well the space shuttle starts at zilch, and i am sure it's a good 30 sec before it is even going 1000mph, I understand it is increasing in speed as it goes, but still, the further you get away from the "core" the lower the gravity, so I mean if you say yeah, the speed is increasing but apparently there is a cut off as to how long you have to reach that magical 25,000mph is it a minute, it can't be 10,or 100 because even at a lower speed then that you would still be free of the earth, as in very far from the core, and free of earths gravity, I always thought to go "straight" up you just need to have more thrust than the weight of your ship, from what I understand the "Falcon" jet can go true verticael as it has more thrust than weight(it's engines need air so it is not a rocket ship though)
What about the material from a Newtron star is that quoted cubic inch weight, on the star or anywhere, say if you took a chunk to earth
Wyclef on 31/3/2006 at 07:18
Yes, "escape velocity" is not a particularly useful concept when we're dealing with rockets with thrust. Rockets can "escape" at any speed, after all, if they're exerting just enough force to counteract gravity. Nevertheless, I supplied a clear explanation, even if the concept wasn't precisely what he had in mind.
