Why is reaching escape velocity the only way to leave a planet or star?

Question

The escape velocity is calculated from a planet's or star's surface.

If one used powered flight to maintain a constant velocity 1/100 the surface escape velocity, you would eventually be far enough away from the body so the gravity could no longer pull you back.

By this logic, a powered spacecraft might also escape from a black hole, as it would not be necessary to achieve a small fraction of the escape velocity to escape. Assuming of course, that one had some way of protecting the spacecraft and occupants from the tidal and other hazards of being close to a black hole.

Answer 1

If you had the means of achieving thrust for an indefinite period of time, with thrust just equal to the pull of gravity plus a small delta, the sum total of all this excess thrust would be equal to escape velocity by the time you get out of the gravity well.
Escape velocity is defined as the speed you need to have where you are to be able to make it out of the gravity well with zero speed left, i.e. zero speed at infinity.

Now, if you want to pull out of a black hole gravitational pull, and that you are already beyond the event's horizon, the acceleration you need just to stay there is infinite, you need your small increment of velocity to be higher than the speed of light. Note that if you are far enough from a black hole, outside of the event's horizon, then the same rule that applies to a planet or a star is valid: you CAN get away, if you have enough thrust.

Answer 2

Escape velocity is actually a rather simple concept. Either an object has enough kinetic energy (velocity) to be converted into potential energy (elevation) to escape a planet or it will fall back to earth. Throw a baseball up in the air and it will return to earth because it was not initially traveling at about seven miles per second (neglecting wind resistance). As the baseball rises it's kinetic energy is converted to potential energy as it slows down (and no energy is lost!). Of course, a rocket with a nearly inexhaustible supply of energy could add enough energy to initial velocity to escape. A black hole is an entirely different animal! Within a black hole (time horizon) space is so curved that if a photon is thrown up (by a flashlight?) it will have too little initial velocity (the speed of light) to escape and will return toward the center of the black hole where all matter is condensed into a singularity so dense that it could occupy the period at the end of this sentence(.) The gravitational attraction of such concentrated mass is great and approachable, whereas we are limited to approaching the earth's center of gravity by the earth's surface (not to mention the heat with depth). If the earth's mass could be condensed into a singularity it too would be a black hole (and invisible in space).

Answer 3

If you flew at 1/100th the escape velocity in a vertical direction, you would eventually escape the gravity, yes, but you would be under powered flight constantly and need more fuel than is probably available on the earth by the time you left the gravity well.

Escape velocity means you get to that speed, turn off the thrust and you're free.

By your logic, you could never escape a black hole since the escape velocity exceeds the speed of light.... no cigar on that one.

Answer 4

You never get beyond a planet's (or star's) gravity. Gravity goes to infinity. It does, however, diminish as the square of the distance increases.

The escape speed is directly related to the gravity. As you move away from a planet (or star), the escape speed is less. At Earth's surface, the escape speed is 11.2 km/s.

As you move away from Earth's surface, the escape speed is less and less (never 0 in theory but, in reality, you can get far enough that some other planet's (or star's) field becomes stronger than Earth's).

Therefore, by keeping a constant speed of 0.01 * Escape-at-Surface, you will eventually reach the escape speed for the distance you are at.

Then you will have escaped.

Answer 5

There is more to a black hole than merely its escape velocity, although it's interesting that a Newtonian calculation of the escape velocity accurately predicts the location of the Event Horizon.

In GR, however, spacetime itself is curved by gravity. This means that starting from any point within the event horizon, all possible trajectories lead eventually to the singularity, regardless of velocity.

Answer 6

i'm going to respond to interior the order in which you asked: a million) via escaping Earths orbit slowly. The orbits get extra suitable and extra suitable till the craft is close adequate to its trip spot to orbit it. Then the alternative happens. Orbits get smaller and smaller around its trip spot till its close adequate to land. this is all calculated in boost interior the case of a aim at the same time with a planet or moon. 2) via timing the launch so as that the 'aim' (moon, planet or famous individual) would be the place the rocket is via the time it gets there. honestly aiming at a shifting aim, so which you may desire to purpose previous to it. 3) there is at present a rocket going to Mars carrying the hot 'interest' rover. this is going to be touchdown there August 5th of this year. 4) definite, they do have controls to shift guidelines for manned area flight (like the moon missions and area trip). Unmanned craft (which comprise satellites) even have administration via ability of telemetry. In the two circumstances there is typically no longer numerous extra gasoline, as a results of launch weight, so basically minor corrections are made. this is why the domicile windows of maximum launches is serious. New ion (electric) engines might replace this interior the destiny. 5) definite, they might decelerate the cost, besides the shown fact that it makes use of numerous gasoline so they frequently might desire to get it appropriate the 1st time. All area craft the two might desire to be accelerated or bogged right down to realize their trip spot or orbit completely. > look at nasa.gov... this is an exceedingly relaxing website to wander away on :P

Answer 7

Wrong it will not work the longer u fight the gravity the more fuel u will use. Trying to escape a black hole that is a joke. It is like climbing a Lauder will not work.

Answer 8

that is necessary in order to achieve at least a parabolic trajectory...which is obvious.

Answer 9

Good thinking