Is the speed of 25,000 MPH really necessary to achieve escape from earths gravitation?

Question

Surely, if a body is propelled verticaly from Earth, even at a low speed; as long as this force is kept applied for long enough, wouldn't the time come when the body would be free from gravity and travel on even when the force has ceased?

Thanks for the wealth of answers. Great. Perhaps I should be a bit more specific.

Surely with a light enough craft with a sufficient reaction mass ( maybe some sort of future fusion reactor) it would be possible to continue at a low velocity and eventualy out of the influence of the earth's gravity.

Am I breaking any laws of physics in this theoretical mind-experiment?

Answer 1

You're actually right. Furthermore, escape velocity is a function of distance from the center of mass (of the Earth in this case)

Escape velocity applies to ballistic motion.

V(esc.)=(2G*M/r)^1/2

Where G is the gravitational constant
M is the mass of Earth (in this case)
And r is the initial radius from Earth's center from which you are computing escape velocity.

Answer 2

No. The force must be powerful enough to break free of earth's gravity. A lesser force that only propels you to a lower speed will not be sufficient and you will only get into orbit around the earth or fall back to earth if it is not enough to maintain an orbit.

It's also important not to confuse force with speed. A small force can eventually propel you to a very high speed if it is able to overcome other forces acting against it. If your question is referring to that situation, the constant force applied to the object must be enough to lift it off the earth's surface and then it will eventually reach escape velocity.

On the other hand, there is an idea to build a "space ladder" using carbon nanotubes attached to a counter-mass in orbit where we could then get things into orbit by simply climbing the ladder at any speed. But this technology is a long way off.

Answer 3

In order to escape from Earth's gravity an object must reach a speed of 25,038.72 MPH (miles per hour). If an object does not reach this velocity, no matter how long it tried or how much energy is used, it would never be able to escape Earth's gravity. The only possible way around this would be to launch an object at the Earth's equator toward's the east (travelling with the Earth's spin) and then the escape velocity would be reduced to 23,920.92 MPH.

Answer 4

Picture throwing a baseball as hard as you can. If you throw it 50 miles an hour, it will travel horizontally few hundred feet and arc toward the Earth until it hits ground. If you throw it 1,000 miles an hour (if you could) it might travel a few miles but still eventually arc toward Earth and hit. No matter how fast you throw it, you'll keep getting bigger arcs but eventually it'll hit the ground. At some point, just under 25,000 miles per hour, the arc you throw will be so great, it will follow the curvature of the Earth. This is the point where it is in orbit. It will just keep falling in that arc around the Earth forever until something stops it. Now, if you throw it fast enough, it will no longer arc to Earth-- that's escape velocity.



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Terry F-- Quite wrong-- opposite in fact. The speed IS for escape velocity. The FASER it goes, the more chance of burning up-- not slow. It could burn up from coming in on too steep an angle, and therefore too fast.

Answer 5

The speed is a factor. Once you reach orbit, you're ability to propel within the vacuum of space is greatly reduced and you become slowed by gravity very quickly. If you don't have a certain speed to break the threshold of gravitation vs momentum, then you will even tually stop and be pulled back to earth. So there is definately a certain speed required, but i dont' know if it's 25,ooo mph.

Answer 6

25,000 mph is the orbital velocity, which is the speed required to circle the Earth in low Earth orbit. About twice as fast is ecape velocity, which is the speed that must be achieved to escape to infinity without continuous thrust. This is the most fuel efficient way to escape the Earth's gravity field because continuous, slow burns mean you are accelerating the fuel mass for a long time. It's most efficient to burn as much fuel as possible in one mighty orgy of acceleration.

Answer 7

tie a weight to a string , hold it out at 1 arms length fro your body, so it hangs down to about 6 inches from the ground.

Spin around at 1 speed and note how high the weight rose.

now double that speed and note how high the weight rose.

Do you think if you spun at the first rate for a longer amt of time , that the weight would rise as far as the faster speed?

The answer is no it wont. Nor will a rocket acquire the force needed to counter gravity by simply applying the same force for a longer time period.

Answer 8

Yes, if you kept pushing all the time, you could get away from Earth at any arbitrarily slow speed. But even at very great distances there is some tiny pull from Earth's gravity, so you could never stop dead anywhere in space and not slowly start falling again. In theory, at infinite distance the escape velocity is 0, but you can never be infinitely far away.

Answer 9

The key is unpowered orbit.

If you have an infinite source of power and infinite reaction mass you can achieve and maintain all kinds of unstable orbits.

Most lauunches work more like a bullet. They are accellerated for a fairly short period and after that they are unpowered and coasting. If you think of rocket launch velocity like bullet muzzle veloicty you can see how the speed is required.

Answer 10

it really is the get away speed, i.e.: if I threw a stone instantly up, it would favor to be going that quickly (because it left my hand) to flee the earth's gravitational pull, as quickly because it has left my hand no longer something is pushing it. you may want to holiday at a million mph see you later as you had a consistent rigidity. it really is neglecting air resistance to boot that cost.

Answer 11

I agree with you. Maybe it's the force required to go 25,000 mph is the force required to break through the gravity's pull.