# why do things orbit in outer space?

I know that the smaller object is pulled in by the gravity of the larger object but the smaller object must have some kind of counter-acting force on its own which propels it around in a circle instead of collapsing into the object. What keeps the object moving? Will the smaller object eventually crash into the greater object?

Relevance

Will the smaller object eventually crash into the greater object?

Yes, this is why we have meteors that crash into earth. Also, whenever the space shuttle come back into earth's atmosphere, it uses earth's gravity to help it get in.

Think of it like this:

You have a ball on a string. Your swinging the ball around over your head. Your hand acts as the greater object, the string represents gravity, and the ball represents the smaller object. Whenever you swing the ball around, the string is pulling on the ball, however, centripetal force is also pulling on the ball in the opposite direction, which keeps in the same orbit since the forces acting on the ball are the same. This is equilibrium. However, when the gravitational force becomes greater than the centripetal force, the object falls into the atmosphere of the greater object with the gravitational pull.

You're exactly right -- there's something acting on an orbiting object that counteracts the larger object's gravity. And the force that propels it is inertia, or momentum. An orbit reflects the balance between the object's momentum and the gravity of the thing it is orbiting.

Newton's second law of motion describes this: A body at motion will tend to remain in motion, unless acted on by an outside force. So an orbiting body -- the shuttle, the ISS, the Moon, or looking a little larger, the Earth as it orbits around the Sun -- is clearly in motion. As a moving object, it has momentum -- the tendency to remain in motion, just like your car keeps rolling if you get off the gas.

But even in space, the orbiting object is acted on by an outside force: the gravity of the Earth, in the case of the Moon, the shuttle and the ISS. Gravity is constantly pulling these orbiting objects toward the Earth -- in a very real sense, the ISS is continually "falling" towards the Earth, but it stays in orbit because its momentum very closely balances the attraction of gravity.

Will the smaller object eventually crash into the larger? Not necessarily -- the Moon is actually moving AWAY from the Earth. The determining factor is how closely the forces of momentum and gravity are balanced. If you have more momentum than gravity, the smaller object will gradually move away from the object it is orbiting. If you have less momentum than gravity, the smaller object will eventually crash into the object it's orbiting. And calculating the exact velocity required to achieve this balance is one of the things that makes rocket scientists rocket scientists.

• Anonymous

Objects want to keep moving in the same direction. Only when a force is applied, this direction changes. So, the normal behavior would be to move in a straight line, with no change in speed or direction.

Both objects pull each other. The smallest object (more precise: the lighter one) doesn't influence the larger (heavier) one much. In most cases it is hardly noticeable. For all practicable purposes, we can assume only the large object is pulling the small object in.

The moon is moving west to east. If it would move in a straight line, the distance to the center of the earth would increase, and eventually the moon would be gone.

If the moon would have no forward velocity at all, then as soon as the earth starts pulling, the moon would fall in a straight line to the center of the earth.

The combination of these two movements makes that the moon falls towards the earth just enough to cancel the moving away from earth. The distance to the center of the earth stays the same (more or less) and the result is an orbit.

Not all objects will orbit:

Sometimes gravitational pull is too strong when compared to the original speed. In such a case, the small object will eventually collide with the larger one.

In other cases, the gravitational pull is not strong enough. The small object will be moving in another direction but will move away from the large object.

Only when the gravitational pull and the forward speed of the object are matched, the result is an orbit.

Will the smaller object eventually crash? No! For instance, the moon is slowly moving away from earth, and eventually it will escape earth's gravitational field.

What one poster said above is wrong; it is not true that there is no gravity in space.

Objects orbit because their forward momentum is fast enough that the object falls around the Earth instead of falling toward it (actually, the object is falling toward the Earth, but it is moving forward at the same time, so the direction of "down" keeps changing due to the fact that the Earth is round).

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...In this diagram you can see that the shell is going far enough to actually follow the curve of the earth for a period of time before hitting the ground.

One thing that gums these examples up is air resistance, so imagine that you took this cannon to the moon and mounted it on top of the highest mountain. The moon has no atmosphere and is completely surrounded by the vacuum of space. If you adjusted the speed of the shell just right and shot the cannon, the shell would follow the curve of the moon perfectly. It would fall at exactly the same rate that the curve of the moon falls away from it, so it would never hit the ground. Eventually it would curve all the way around the moon and ram right into the back of the cannon! On the moon you could actually have satellites in extremely low orbits like that -- just a mile or two off the ground to avoid the mountains. And satellites could conceivably be launched from cannons.

On earth, it's not so easy because satellites have to get up above the atmosphere and into the vacuum of space to orbit for any length of time. 200 miles (320 km) up is about the minimum to avoid atmospheric interference. The Hubble space telescope orbits at an altitude of 380 miles (600 km) or so. But the principle is exactly the same. The speed of the satellite is adjusted so that it falls to earth at the same rate that the curve of the earth falls away from the satellite. The satellite is perpetually falling, but it never hits the ground! ...

• iMi
Lv 4

Whoa.

There are actually two things that keep objects in orbit. Gravity pulling it in as you've mentioned and the object's velocity. While the object's tangential velocity keeps trying to push it away in a straight line, gravity keeps pulling it in. See this illustration: http://sol.sci.uop.edu/~jfalward/physics17/chapter...

You can imagine there that if you were the sun and you were swinging that green ball around on a string that you are pulling it towards you (like gravity) but there is also a sideways velocity swinging it away. If you let go of the string the ball would fly away in the direction of this tangential velocity.

The centripetal force is just kind of an outcome of this motion.

Another way to help you visualize it is to think of an object being caught by the gravity of another object. It moves along in a straight line (assuming nothing else is acting on it), it's velocity is in this direction. When it gets near the gravity source it is pulled in to it, it looks like it is still trying to run away but the gravity source has it on a leash and is slowly shortening it, pulling it in.

A smaller object will not necessarily crash into the larger object, it depends on where it entered the orbit (I think microsoft encarta has a little game you can play to help visualize this). If it is headed towards the larger object it will crash into it (obviously if it is headed straight towards the larger object it will crash straight into it). If it is moving quickly enough and is not aimed at the larger object, the larger object's gravity can still act on it but not pull it into an orbit... it will briefly be tugged in towards it, then escape. There is a happy medium, where if it hits the gravity perfectly it will stay in a stable orbit. Many moons of planets (including our own, have decaying orbits that will allow them to eventually escape from the gravitational pull of the planet: their tangential velocity is too great to be balanced by the planet's pull of gravity.

Source(s): Astrophysics student
• Anonymous

Many things contribute to this:

the gravitational force of the big object is what brings the small one into orbit. But the gravitational force can only be strong enough to bring it in a certain distance. On top of that the Centripital Force of the smaller object also helps keep it at a semi-steady distance. As-well as the gravitational pull of other astronomical bodies in space

• 4 years ago

there's no particular distance required so you may be in orbit a pair of planet, and your mass won't remember. that's, different than for sensible concerns mutually with being severe adequate above the ambience to decrease drag, and that your mass is tiny while in comparison with the planet's mass. based upon your preliminary velocity and direction of action out of your beginning element, the planet's gravity will reason you to stick to a direction which will take the form of the two an ellipse or hyperbola. Hyperbolic orbits happen once you have adequate ability to start with to coast all a thank you to infinity from the place you started. in case you have much less ability than that your orbit will take the form of an ellipse. If that ellipse would not intersect the planet's floor, then you will flow around and around encircling the planet. If the planet is in the way you will crash into it. If there is extra beneficial than one planet on your place then you are plagued by employing the vector sum of the forces that each and each planet applies to you. when you consider that gravity decreases in capability by employing the sq. of the area from the source, the closer planet will impression you much extra strongly than the some distance one in the event that they have comparable lots. however, there'll continually be a place the place each and each impacts you the two and in opposite guidelines so there will be 0 internet tension.

Two objects orbit each other around their center of mass. The earth and sun orbit around the center of mass of the two objects. Because the sun is so much larger, the center of mass is actually inside the sun's sphere. Hence, it appears that the earth orbits the sun, when in fact they both orbit their center of mass.

And space is curved by their masses too. They travel around the curvature of space.

Source(s): Myself