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Known since prehistoric times, it is the brightest object in the sky after the Sun. Capture and retention of primordial gases In evolution of the atmosphere: Escape exosphere In exosphere. Help us improve this article! Contact our editors with your feedback. You may find it helpful to search within the site to see how similar or related subjects are covered.
Any text you add should be original, not copied from other sources. At the bottom of the article, feel free to list any sources that support your changes, so that we can fully understand their context. As it rises up, gravity tugs on it and it slows down. As it gets further away, gravity diminishes so it decelerates more slowly. Eventually, it gets to some distance where it has come to a stop, but Earth's gravity no longer has any effect on it.
The velocity our object had at Earth's surface is Earth's escape velocity. In precise terms, a body's escape velocity is the velocity an object in "free fall" must have in order to escape the gravitational influence of that body - no more and no less. Technically, escape velocity can be specified for any distance from the center of a body, and the value will decrease with distance, but when a planet's escape velocity is stated, it is usually for the planet's surface.
Mathematically, it is calculated as an integral of the body's gravitational acceleration from some specified distance to infinity. An object does not have to travel at escape velocity to escape a planet's gravity, but the same amount of energy needed to accelerate an object to escape velocity must be applied to an object giving it potential energy to lift it out of the planet's gravitational sphere of influence.
The difference is that at escape velocity, the object needs no external influence to escape; at anything less than escape velocity, some external force must be applied. Escape velocity reduces as you get further away from the Earth. If you proceed upwards at a constant speed of 1 mph which as noted will require continuous thrust to counteract gravity , you will eventually reach a distance where the escape velocity is equal to 1 mph. Then, you will have reached escape velocity and are no longer gravitationally bound to the Earth.
In practice, third-body effects moon, sun, other planets will dominate when you get beyond 10 5 km away from the Earth. To sum up the answers: That is, if you are AU from Earth, you don't need any more fuel to counteract Earth's gravity, you just float away. However, when at Earth's surface, you will need additional acceleration to sustain the 1mph velocity - otherwise you just fall back down like the tossed ball. You are confusing velocity and acceleration. If you have a high enough velocity, the effect of de acceleration can not slow you down before you get far enough away from the gravitational source.
The problem is that would require constant thrust. The escape velocity is only for objects thrown projected into space , with the initial velocity and they are not powered. Escape velocity is the speed at which you'll leave the Earth and not return if you don't continue to propel your craft. Below that speed, gravity will pull you back down.
What is escape velocity?
XKCD's got one of the more accessible explanations. The key difference is that "escape velocity" is how fast you would have to throw a stone straight up from the Earth's surface ignoring air drag , for it to escape from Earth's gravitational influence.
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It would be coasting the whole way, always losing speed due to Earth's gravitational pull. If, on the other hand, you have a rocket engine with sufficient fuel, you can just keep rising slowly 1 mph , which is almost a hover, until you've gotten way out into space and Earth's gravity is overwhelmed by the Sun, Jupiter, etc. You could keep throttling back to maintain the same upward speed gravity decreases with distance, and the rocket carries less fuel if you wanted to, or let the rocket speed up.
Unless you are very far away from Earth, if you are only moving away at 1 mph the gravity of Earth will pull you back to Earth assuming you do not have an infinite fuel supply to maintain a 1mph thrust. So you are correct when you say. Is it because the object has to gain a certain speed once it reaches orbit in order to maintain that altitude. Think of a ball tossed in the air, it starts by moving quickly, but as it rises higher it goes slower, than stops and falls back down. At some point it is moving away from Earth at 1mph, but gravity overcomes that momentum. Air Resistance has some impact on the ball, but you can throw horizontally much farther than you can up.
Gravity works pretty much them same on the surface of the Earth as it does a miles up. When you throw something horizontally it falls towards the earth in an arc, attracted by the gravity of the Earth. If it is moving fast enough the curvature of the Earth will match the arc of the falling object, this is called Orbital speed and the object will not hit the earth. If you had a nearly infinite fuel supply, and you kept moving away from Earth at 1 mph, yes you could escape.
You could do this with a solar sail there are a couple of issues using the sail near Earth but assuming you start in a high stable orbit, you could easily expand until your escape. Of note, using a solar sail, as you move farther from Earth your speed would increase unless you lowered the efficiency of the sail. In other words, if you started with a solar sail to get 1 mph thrust, you would need to work to maintain that speed, otherwise you would soon be going faster.
Looking at this in another way, consider the concept of gravity wells. The gravity well of course is not a "real", physical well, but it is a commonly used metaphor to describe how much energy is required to escape from the gravitational effect of a body, and it provides a reasonably straight-forward way of answering your question.
Space buffs, bear with me below; this is meant as an explanation, not a university-level physics and astronomy lecture. If you are at or near the bottom of a gravity well say, at the surface of the Earth and want to climb out of that well, you basically have two options. Either climb very fast for a short distance this is the approach taken for getting off the surface of the Earth, for reasons stated in other answers , or climb slowly for a much longer distance this works once you are far enough away from the body forming the gravity well that the predominant gravitational forces acting on you are small or negligible.
Each way of looking at it represents the same thing: The energy provided as input becomes potential energy as you climb farther from the surface, and at some point, your potential energy exceeds the gravitational pull at that point of the body that forms the gravity well; you "continue on a tangent" and move straight on from that point forward rather than following the curve of the gravity well.
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Once that happens, you have reached escape velocity from that body. If you don't climb far enough for your rate of climb at the time you stop actively climbing, then when you stop climbing let's assume you cannot grab hold of anything, because in space there is nothing to hold on to you will fall back toward the body that forms the gravity well you are trying to climb out of; you did not attain escape velocity. Of course, there are usually multiple gravitational forces to contend with at any one point.
However, one of them will project a stronger force on you than the others; that's the concept behind the sphere of influence.
What is escape velocity?
Near Earth yes, that most definitely includes low Earth orbit , it's Earth's gravity that dominates; take a trip to Luna and its gravity will exert the greater force once you pass the Earth-Moon system L1 Lagrangian point. Hence, the depth of Earth's gravity well is approximately Wikipedia gives the escape velocity at 9, km above the Earth's surface as 7.
To get outside the hill sphere and into "solar space" rather than being in "Earth Space" , you're looking at years of continuous 1. Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site the association bonus does not count.
Would you like to answer one of these unanswered questions instead? Home Questions Tags Users Unanswered. Couldn't I escape Earth's gravity traveling only 1 mph 0.
Escape Velocity
Comments are not for extended discussion; this conversation has been moved to chat. Escape velocity is a mathematical definition. What initial speed do you need to reach infinite distance to the planet. It takes infinite time to get there, but the escape velocity has the necessary kinetic energy for infinity.
To reach a low or higher orbit, less energy and velocity is needed. Anthony X 9, 1 35