weightless in space

[icebread]

when you go into space do you become weightless at an exact height above the earth?

[wildwood]

I believe it is a gradual thing. You don't actually become weightless, you become less influenced by the Earth's gravity. The percentage of 'weightlessness' can be very tricky to calculate as it depends on where you are in relation to Earth but at 200 miles up you loose about 10%.

[Amber63]

..lose about 10%.

[beso]

The weight due to Earth's gravity diminishes only slightly with height. The change in weight when moving away from the centre is an inverse square relationship.

The radius of the earth is about 4000 miles. At an altitude of 200 miles (radius of 4200 miles) the weight is as calculated by wildwood.

However the familiar kind of weightlessness seen on orbiting spacecraft has nothing at all to do with height. It is simply a matter of the craft and its contents moving at the same velocity.

When in orbit both the craft and the occupants are on the same orbit so all travel on the same path and everything inside appears to have no weight.

The height makes very little difference. Theoretically you could become weightless in an orbit just above the surface of the planet. However the orbital velocity for the earth is 18,000 mph so atmospheric friction would quickly slow the craft so in reality you do need to be above the atmosphere.

Weightlessness can also happen when both a craft and its contents are falling together.

An aircraft flying in a parabolic path will cause weightlessness to its occupants. Floating out of your seat in parts of a rollercoaster ride is exactly the same phenomonon.

[jake-the-peg]

Beso's put it very well

Remember the Earth's Gravity keeps the moon in orbit around us and that's a quarter of a million miles away.

You have to go a long way to actually escape the Earth's gravitational pull.

[Rollo]

And you have to go even further to get away from the gravity exerted by the Sun.

[R1Geezer]

the weightless feeling is because orbit is effectively continual freefall, There is no hieght that suddenly gravity is off. In fact the orbit is due to gravity pulling he object down but the object is moving forward fast enough that the curvature falls away at just the right rate. In H2G2 esque, Essentially the art of acheiving freefall lies in throwing yourself at the ground and missing.

[Champagne]

So would a very small, skinny person become weightless before, say, a clinically obese person?

[R1Geezer]

No, Remember Gallileo? The Hammer and feather fall at the same speed. The effect of gravity is due to proximity. The Orbit situation is not the same thing.

[dundurn]

No, if one person is weightless, everybody is weightless! Astronauts don't get weightless until their engines switch off. On Apollo there used to be a short gap during staging where they would float up into their harnesses until the second stage engines would push them back in their seats and the same happened during trans-lunar injection and all the other mid course correction manouevres etc.

[mibn2cweus]

Gravitational attraction between two bodies is not a product but the sum of mutual attraction between their respective masses. In relation to the very large mass of the Earth the difference in mutual gravitation attraction between Earth and two people of different weights is virtually identical. In comparison the Moon's contribution to the mutual gravitational attraction between it and the Earth is only about 1% of the combined total.

In relation to the Earth a feather or a cannon ball experience nearly identical gravitational acceleration. It takes a lot of mass to produce a significant gravitational 'force'.