Question for Physics: Weightless in orbit? Why?

[LarrySamDavid25]

Okay, now I understand that gravity has what we consider to be infinate range. But here's my beef:

http://www.space.com/scienceastronom..._020903-1.html

Now, it says that the effect of weightlessness in orbit is due to the fact that they are constantly freefalling, but continuously barely missing the planet? I find this hard to swallow, as if perhaps they have tried to put it in a way so simple, that it has become bogus. Am I wrong? I don't know. I remember arguing this with my 8th grade teacher, and got it wrong on every test because I refused to except the fact that while in orbit you continuously freefalling towards the earth. Orbitting, yes.

So is the weightlessness due to a bit of a tumble created by both the force of gravity and the velocity or inertia of the orbitting vehicle? And what would the G's equal if a vehicle where in fact maintaining position at one of these orbital heights?

Can anyone help me with this?

[M_Six]

Learn it all at HowStuffWorks.com .

[LarrySamDavid25]

At the correct orbital velocity, gravity exactly balances the satellite's inertia...

not as specific as I was looking for...I'll keep looking.

[LarrySamDavid25]

Well, most the sites state it to be because of being in a freefall. I still think this over simplification is innacurate. Because in what we consider a free fall, you are closing in on an object at the same speed in which it is pulling at you. But in orbit, one is not closing in on the earth, but rather maintaining a constant distance (idealy, providing no decay is in effect, such as in low level orbits due to faint atmospheric friction).

So how fast would one need to orbit to be weightless at say 30000feet?

To maintain an orbit that is 22,223 miles (35,786 km) above Earth, the satellite must orbit at a speed of about 7,000 mph (11,300 kph). That orbital speed and distance permits the satellite to make one revolution in 24 hours.

So here we're maintaining both the orbital heighth, and the perpendicular position over earth. So this object would either incur the effect of weight, or would plumit straight to earth according to this freefall statement, no?

Actually, thinking about it, it's a bit of a paradox here, if you are indeed freefalling. Because in order to feel the effects of gravity here, there would have to be some sort of potential device, supporting the satellite, preventing it from falling, creating a barrier between it and gravity.

I mostly understand the concept of orbit. It's this "freefalling" explanation that I have a tiff with.

[M_Six]

In space there is no air, nothing to slow something down once it's in motion (inertia). The only thing that keeps satellites from flying off into space is gravity. Gravity is pulling the satellite towards the earth with the same amount of force as the satellite's inertia. Hence the orbit. Without gravity to "curve" the flight path of the satellite by pulling it towards the earth, the satellite would go flying off to parts unknown. And without the inertia, the satellite would crash to earth.

[Orbiter]

I feel kind of obligated to take a whack at this one, my name being "Orbiter" and all. I started to type out an answer, but I think you are looking for more than simple explanations and that's about all I have time to give, so try this link out:

http://users.commkey.net/Braeunig/space/orbmech1.htm

I will try to come back and answer any specific questions if you have them. I think the part about centripetal acceleration may have the answer you are looking for.

Enjoy! Orbital Mechanics can be fun!

[daveleau]

The velocity of the orbiter keeps it from crashing into the earth as it falls. Velocity is in a straight line, while the falling due to gravitational pull causes the curvature of the orbit. Once these two values are balanced, the orbiter is in constant free-fall.

F= (Gm1m2)/r2

Force equals the universal gravitational constant times mass of object 1 times mass of object 2 divided by the radius squared. (sorry had to spell it out since we have no subscripts and superscripts.) This is Newton's universal law of gravitation. It states that the gravitational force exerted by a mass (m1) on another mass (m2) is proportional tot he products of their masses and inversely proportional to the square of the separation (r). G= 6.67x10 -11 Nm2/kg2

The force (F) is the force bringing the two objects together in a direct line towards each other. If a velocity in the perpendicular plane is equal to F, then the body will constantly be attracted towards the other mass and the velocity will keep it in constant orbit.

If you take into account the mass of the earth and the close proximity of orbiting objects, the force of gravitational pull is significant and requires a fairly significant velocity.

(glad I kept my college physics book around...)

I hope this helps.
Dave

[nukes]

I was under the impression that gravity puts welds in spacetime and everything sort of rolls around in these. The fact that the planet is moving means that it won't actually hit it and the orbitting object simply continues to be pulled around it.
Hard to think of an example you may have seen.

[Epidemic]

Because!!!

[Theophylact]

Here's another way of looking at it. Imagine that you're in an elevator ten miles up. Someone cuts the cable. You -- and the elevator car -- both fall, accelerating toward the Earth at the same rate. That's free fall; you can float free within the car until you splat.

Now imagine a second car, also dropped from ten miles up. Give this car a big shove westward as the cable is cut. The car will still be in free fall until the splat, but it will splat somewhere west of where it would have without the push.

It'll also take somewhat longer before it splats, because as it falls, the Earth curves away under it. The bigger the shove, the further to the West the car will land.

With a large enough impulse, the car will accelerate towards the Earth exactly as fast as the Earth's curvature recedes from it. The car will then be falling freely towards the Earth without ever hitting it.

That's orbital velocity.