How far must you travel from earth for zero gravity? Zero atmosphere?

Answer 1

There's no such thing as "zero gravity."

There's microgravity, in which things appear to float, but in truth they are still being affected by gravity. Microgravity is a condition--an illusion, really--created by falling. It is created when objects fall together.

This occurs in space, with orbiting shuttles and space stations. Objects in orbit are constantly falling towards the Earth, but never reach it because the Earth is also constantly moving.

Microgravity conditions are also created in airplanes, most notably NASA's "Vomit Comet" planes, a Boeing 727 and a McDonnell Douglas C-9B. These planes fly in parabolic arcs that create conditions of microgravity for a few seconds at a time.

Answer 2

The force of Earth's gravity on "you" or a traveling object is calculated with

F = G * m * M / (d^2)

F is the force
G is a constant (not equal to zero)
m is "your" mass (or the mass of the traveling object) - not zero
M is the mass of the Earth (certainly not zero)
d is the distance between Earth and you
d^2 indicates the distance is squared.

For F to be zero, either one of the factors has to be 0 (like the mass) or the distance has to be infinite.

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Zero atmosphere is different. In theory, the atmosphere keeps getting less and less but never zero. In practice, there is a point where the Earth's atmosphere has a density less than the Sun's "atmosphere" -- the solar wind -- in our vicinity. This happens well before reaching the Moon. The exact distance changes from day to day (because of solar activity. mostly).

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PS:

Weightlessness is not the same as zero gravity (even though even scientists use the expression "zero gravity" when talking about weightlessness).

Even at an altitude of 4,500 km (well above the highest "low orbit" satellites), Earth's gravity is still half of what it is on Earth's surface. The reason an astronaut in orbit at that altitude does not feel weight is because the force of gravity causes him to "fall" around the planet at exactly the same rate as the capsule he is in. It is like being in an elevator that is in free fall.

The elevator is falling just as fast as you are, therefore your feet do not press on the floor.

Kids, don't try this at home.

Answer 3

Both gravity and atmosphere just get less and less with distance but never really go to zero. The atmosphere gets thinner than the solar wind (which is kind of like the Sun's outer atmosphere) at an altitude of a few thousand miles, but that altitude varies tremendously according to solar activity. The Earth's gravity is strong enough to keep the Moon in orbit at a quarter of a million miles away, and strong enough to have affects on the motions of asteroids and space craft that are large enough to be important for millions of miles, but at distances larger than a few million miles the gravity of other objects becomes more important. But theoretically, Earth's gravity never goes to zero at any distance, no matter how far, even billions of light years.

Answer 4

Most people probably don't realize why astronauts float in space. It isn't because gravity is so weak up there that they don't fall. It's because they are falling around the Earth, which is essentially what an orbit is.

At 22,500 miles you are in a geosynchronous orbit (you orbit the Earth at the same angular velocity as the Earth's rotation, allowing you to remain over a specific spot on the Earth's equator). Gravity still affects you here, as you are still in orbit.

Answer 5

If you travel towards the moon a distance of 22,500 miles you will sit in a stationary orbit. Virtually no gravity.
After 30,000 ft the atmosphere drops off rapidly,you can't really say when it is gone completely but satellites orbit at 250 miles with little or no resistance.

Answer 6

Well the thing is that there is a universal equation for gravity that involves mass and distance. since you will always have mass and the earth will always have mass, and there will always be a distance between you two, there will always be some gravity (however it might be so little that you can't notice). and As to Zero atmosphere, that could be achieved, but i don't know the distance.

Answer 7

Bradley has it correct.

Also, it is hard to define zero atmosphere. Even where the ISS orbits, there are millions of molecules of air per cubic metre (down here there are trillions per cu m).

The atmosphere thins out gradually, but nobody could say where there was zero. Even if there were 10 molecules per cu m thousands of kms out, that is nearer to a perfect vacuum than anything we can create down here, but is still some atmosphere.