Does everything produce a gravitational field in zero gravity?

Question

I understand from basic Physics at school that an item must travel at a particular trajectory around another item floating in zero gravity in order to be picked up into orbit. I was taught that satellites are maintained in orbit through physics alone, because they are caught in the gravitational field of Earth, while traveling at a particular angle, which prevents them from ever colliding with the planet. I was also taught that gravitational fields only occur in zero gravity. Does this mean that any item traveling in zero gravity could take things into orbit? For example, could an astronaut, floating in space, place small items into their own orbit? Is orbit determined purely by the size of the orbiting item in relation to the item it orbits, or does an item have to be a certain size to develop or enter orbit?

Answer 1

In general, the answer to all of your questions is yes, but your wording is a bit off. Gravitational fields don't occur in zero gravity - that's like saying that Coke only exists in the absence of Coke.... I'm going to try to explain it all for you, so bear with me.

Any two objects in the universe experience gravitational attraction. If you had a universe that was entirely empty except for two grains of sand, and they were 5 billion light years apart from each other, they would still be attracted to each other, and eventually collide.

Take those same two grains of sand and put them just as far apart in our universe. They still experience the same gravitational attraction, it's just that each would be MORE attracted to something else closer and more massive, which would prevent them from bringing each other together.

What you're thinking of by "zero gravity" is more correctly referred to as "microgravity" (which is actually a misleading term). In any region of space, one particular object (or collection of them) will have a gravity field that dominates all others present. Yes, the astronaut's pen floating beside her is attracted to her by gravity, but the Earth's gravity is the dominant field while in Erath orbit, so the pen and the astronaut are both orbiting the Earth and not each other.

Earth's gravity is actually still mostly as strong in orbit as it is on the surface - what do you think keeps the Moon where it is, and the space shuttle from flying off into space?

Once a space craft does escape Earth's gravity, the Sun's gravity becomes the dominant field. Outside the Solar System, the galaxy's combined gravity becomes dominant. On your way out, you may swing by Jupiter for a boost. While near Jupiter, its gravity is dominant and your motion is changed by that gravity. Once you escape that on your way out, you're back in the Sun's gravity field until you get far enough away to be in the galactic gravity field.

Actually, you're always in the Sun's gravity, the Moon's gravity, the Galaxy's gravity, and the gravity of some pebble sitting on the surface of Mars. It's just that wherever you are, one field will be stronger than the rest and will be the dominant gravitational force affecting your motion.

There is nowhere in the universe that has zero gravity. The reason you don't feel it in the space shuttle is that you're both equally effected by Earth's gravity, and the difference between you and your surroundings is zero. On Earth, sitting in your living room, the floor is not able to fall any further than the ground, so it is "pushing back" against you as gravity pulls you downward.

As far as the orbiting objects around an astronaut, you would have to be VERY remote from the rest of the universe before your own gravity with the pen would be stronger than any other gravitational field in the universe. Assuming you were, though, the pen would have to be moving VERY slowly to be in a stable orbit.

Speed and gravity determine the size of an orbit. Since the mass of you and the pen are constant, the remaining variables are the speed of the pen, yes the direction of the pen, and how far away from you the pen is. A pen would probably take weeks or months to orbit you due to gravity, even sufficiently far from the rest of the universe that your gravity is the strongest field affecting the pen.

If you're willing to spend some time reading to learn it more, then here is an excellent document: http://www2.jpl.nasa.gov/basics/

The basics of space flight can tell you a LOT about how orbits work and much much more. It's broken up by subject matter, so if matters of time and communications don't interest you, just don't read those parts.

Enjoy!

Answer 2

You got some misleading information. There is no "zero gravity" zone. Anywhere you are in the solar system, you are under the influence of gravity. Within about 200,000 miles of the earth, it is the strongest gravitational influence. Get farther away and the sun's gravity becomes stronger than the earth's, (if you are in that direction.) And we are constantly under the strong influence of the Milky Way's collective gravity.

Things stay in orbit because there is a balance between their forward speed and the gravity of the object they are orbiting. Gravity will exist wherever there is a mass. And the amount of gravity experienced will be a matter of how massive and how far away the masses are.

Small objects could orbit something the size of a human, but the gravity is so weak that any movement on the part of the astronaut would leave the particle behind. The orbital period of an object around something like a human would be exceedingly slow, and any disturbance at all would break up the system.

Answer 3

All objects that have mass produce a gravitational field of their own. This is whether they are in the gravitational field of any other object, or not. Since in effect gravitational fields are infinite in extent, we are in the field of the furthest visible galaxy right now. Mass, not size.

If you think about it gravitation fields cannot occur in zero gravity. If there is a gravitational field, then you do not have zero gravity. Again, we are in the grav. field of the furthest galaxy right now let alone nearby stars like Sirius.

Yes, it is hypothetically possible for an object, say a ball bearing, to orbit an astronaut in free space. However the orbital speed would be so slow we would have trouble seeing it move at all. In all likelihood the astronaut would get bored and slope off to do something else more interesting, like watching paint dry.

Since an astronaut is an irregular object, has a variety of mass concentrations and gets bored, we could substitute a ball of iron of the same mass. Then we would have a simpler model and it would be possible to calculate the orbital speed of the ball bearing in relation to the iron ball of 1 astronaut mass from Newton's laws. It would be almost impossible to get the bearing to travel at the correct very slow speed as a practical consideration though.

Answer 4

Everything with mass (solids, liquids, gases) has gravity, and has it whether it is in "zero gravity" or not. Remember, though, that gravity is considered a weak force. It may not seem like it, but compared to the other forces around (like electromagnetism and nuclear forces), it is considerably weaker. It takes a mass the size of the earth to exert 1 G, which is easily overcome by a magnet weighing 1 ounce.

So an astronaut would have her/his own gravity, and an object could go into orbit. But the gravitational field would be very, very weak, and it would take very little additional force to cause the object to achieve escape velocity and leave orbit. The orbit is determined by the mass of the two objects (hence the total gravitational attraction between them) and their velocity relative to each other.

Answer 5

Everything has its own gravitational field, in proportion to its mass. There is no such thing as "zero gravity". Objects in space or on Earth respond to all the gravitational fields around them. In space, there is no resistance, so objects fall (or orbit) freely. Here on Earth the surface of the planet resists our falling through it, so we experience Earth's gravity as a static force rather than an acceleration. There is still a gravitational attraction between your sofa and your television, but it's too weak to notice.

For an astronaut floating in space, his gravitational field is so much weaker than the earth's that nothing can orbit him. If he were somewhere in empty intergalactic space, his gravitational field might be the strongest thing for some distance, and objects within that range either orbit him or fall into him if their relative velocity was below escape velocity. But escape velocity for a 100kg mass is very small!

Answer 6

Absolutely.

However, it's not size that determines where an object can orbit, it's mass. So, a ball, moving very slowly, *could* orbit a man at a distance of say, 6 feet. Or 10 feet if it was moving even slower.

Likewise, say that "man" in the spacesuit is really a mass of lead shaped like a man - then, the orbits at 6 feet and 10 feet would still be there, but since the mass they're orbiting is much more, they'd have to move faster in order to maintain that orbit.

Answer 7

OK... some of the things you were taught or that you picked up are incorrect. Let's start with the main one:

"I was also taught that gravitational fields only occur in zero gravity."

That is exactly the opposite of reality. Every mass gravitates and it does so completely independently of other masses, electromagnetic fields, chemical composition or any other influence imaginable!

In physics this is called "the weak equivalence principle" and it is absolutely fundamental for our understanding of gravity. It has also been experimentally verified with extreme precision.

http://en.wikipedia.org/wiki/Equivalence_principle

The language used in that article needs a little getting used to. You have to have a pretty firm understanding of what "inertial systems", "reference frames" etc. are. But the essence of it is that gravity only depends on one thing: mass. Nothing else matters!

So 1 kg mass sitting next to you at a distance of 1m will attract you with the same force, no matter if it is here on Earth, in the Space Shuttle in orbit or floating in a balloon in Jupiter's atmosphere.

From this it follows that orbital parameters only depend on your relative velocity to the attracting body. If you show me something outside of Earth's atmosphere and let me make one position and one velocity measurement, I will know exactly if that thing is in orbit or not.

OK... let's say you are in orbit and you would have an infinitely strong thread (Spiderman to the rescue!) of negligible mass. That thread, by the way, is called a "tether" and it is seriously investigated as a means of launching spacecraft into the solar system.

So if you had such a tether, could you pull something else into orbit with it? Yes, you could. But by doing so, you would lose altitude. And if you tried to pull a heavy object up to you, it would actually pull you down into the atmosphere or make you collide with the surface!

There is no free lunch, not even for orbiting astronauts. If you want to get something into orbit, you have to invest the energy to speed it up to orbital speed. Where that energy comes from, does not matter.

Hope this helps.

Answer 8

Anything that has mass has a gravitational field, so yes, something very small (maybe the size of a smoke particle or smaller) could orbit around an astronaut in the vacuum of space.

Answer 9

YES! do you lack education? The big bang created the universe and world and evolution produced the plant life and gave man enough intelligence to be able to use that plant to make tea! The Pope, Catholic Church, Church of England and mainstream churches all accept the big bang and evolution! Lord Carey the former Archbishop of Canterbury put it rather well – “Creationism is the fruit of a fundamentalist approach to scripture, ignoring scholarship and critical learning, and confusing different understandings of truth”! Nice that Christians and atheists can agree and laugh together even if it is at fundie expense! But behind the laughter is the despair at the fundamentalists striving so hard to destroy Christianity by turning it from a religion to an ideology! Surveys suggest that 29% of American Christians are so extremist in their beliefs that they fall well outside of the accepted bounds of Christianity! But the question is why do you post like you do? Just immaturity or a desire to make Christianity into a laughingstock?!

Answer 10

Yes, exactly. Just as the new Japanese and Chinese satellites are orbiting the Moon which is orbiting Earth which is orbiting the Sun, a man space walking (floating really) in space COULD have another smaller object orbiting around his body. But the gravity would be EXTREMELY weak so the orbit would be EXTREMELY slow and prone to disturbances of all kinds.