Were you taught incorrectly about Escape Velocity?

Question

Why do so many people think you can't go into space, or go to the moon, unless you are traveling at a super-fast "Escape Velocity"? I happen to know that if you had a ladder long enough, a ladder-climbing astronaut turtle could merrily climb right past the stratosphere, past the moon, past Pluto, and on to the Andromeda galaxy, never going faster than a turtle can climb a ladder.

Do you suffer this misconception? Are school teachers to blame? Are you going to argue with me?

PS - It's one of them ladders with its own support legs, of course!

PPS. Friends, read Bramblyspam's comment about a "continual power source" to understand my point. You can easily go to the moon on a very slow moving spaceship with an engine, no ladder required.

Answer 1

"Escape velocity" implies there is no acceleration acting on the object, aside from gravity. It's the speed an object must be traveling in order to escape the earth's gravitational pull.

You could make a spacecraft that would only travel at 5 miles per hour straight upward, but the test of "escape velocity" is what happens when you shut off the engine. If it falls back to Earth, it hasn't achieved escape velocity. Of course, if you go someplace past Pluto, the Earth's gravitational pull is so weak that a velocity of 5mph may be enough to escape even after you turn off the engines. (The sun's gravity field would be another matter, but let's not quibble). Escape velocity really is dependent on how far away you are from the center of the gravity field.

A turtle climbing a ladder would have a continual power source (=turtle legs) acting to move it away from the Earth, so the term "escape velocity" doesn't apply. If the turtle can let go of the ladder without falling back to Earth, then it has achieved escape velocity.

Anyway, to answer the question: No, I don't suffer from that misconception. I guess I had a good physics teacher or something.

Answer 2

Yes, it is entirely possible for a turtle to crawl up a ladder into outer space. However when launching a payload, you don't have a ladder, and something heavy, (ex. a satellite) can't climb up a ladder. In this application, you need a certain velocity in order to escape Earth's gravitational pull. Otherwise, the rocket, cannonball, astronaut, etc. would be overcome by gravity and fall back to earth. This is much like if a person was to throw a rock up in the air. Without enough velocity, it will fall back to earth. Now, if that same rock could "crawl" up an incredibly tall ladder, at the same rate that you threw it, yes, it could escape earth.

Alas, neither rocks or rockets have legs, nor do we have 5 mile high ladders, so, we have to rely on launching things with enough force to attain "escape velocity."

Answer 3

There's a big flaw in your premise. If the object takes an infinite time to lose the initial velocity, then there is no time after infinity for it to fall back, is there? Escape velocities are more practical than that anyway, because any object launched in any direction from any planet will eventually come across something else with its own gravity. A more practical definition of escape velocity is the speed needed to reach a point where another body's gravitational attraction becomes dominant.

Answer 4

Ok, I'll clarify this a bit more. Escape velocity is defined as the velocity at which a ballistic object (i.e. one that's not using an engine) will achieve a parabolic escape orbit. It's a function of the distance the object is from the center of the body it's orbiting.

If the object has a velocity lower than escape velocity, it doesn't necessarily mean that the object will come crashing back to Earth. What it means is that the object is in an elliptical or circular orbit. Ignoring atmospheric drag, the object will only crash into Earth if the orbit intersects with Earth's surface.

Conversely, if the object has a velocity higher than escape velocity, that means it's in a hyperbolic escape orbit.

As an interesting side note, you don't need to achieve escape velocity to reach the moon. Although there's nothing stopping you from using an escape trajectory to reach the moon if you wish, all you need to get to the moon is a sufficiently large elliptical trajectory, as the moon is in orbit around the Earth.

Answer 5

Yes you could climb slowly to escape the earths gravity until it was balanced or at the mercy of the the gravitational pull of another body. here it gets complicated because we have the sun and other planets all having an influence. However a certain velocity is required to achieve an orbital speed in which the centrifugal force balances the gravitational pull of the earth and a stable orbit is achieved

Answer 6

Your idea would work if such a ladder could be built. The problem is that it cannot. Escape velocity is needed to go into space because you are pushing against air. Escape velocity is the speed you need to overcome gravity and friction resistance. Escape velocity is reality, your ladder is not.

Answer 7

You are quite correct. To clarify, if you wanted to shoot a bullet to the Moon, its muzzle velocity would have to exceed escape velocity to avoid falling back to Earth. It's also the impact speed of an object falling to Earth from a very great distance. Ignoring air resistance in both cases, which of course you can't do at 7 miles per second!

Answer 8

You can provided you climb up with a varierty of gadets to keep you alive namely oxygen and clothes to keep you warm and of course keep you feeding at high altitude. And of couse you need to assembly ladders which is not possible to be built because you need ladders which are a few hundred miles long.Technically impossible but theoritically possible for argument sake.

Answer 9

i think you are confused here. escape velocity is the speed required by an object to get out of earth (or any other planet, star, etc) without any support.
any thing going at the escape velocity (or faster) will not fall back, any thing going slower than that would fall back. but it is not the only way to get out of a gravitaional field. (at least is theory).

Answer 10

All these years, and I never knew the truth. My life is finally complete. Thank you ever so much!