# Orbiting earth

## Main Question or Discussion Point

orbiting earth!!!

Hope iposted this question in the right spot!!!!.
If i launched something in space and then stopped its forward momentum
wouldnt the earth gradually move away from it and pick it up again so to speak..a year later???

Related Classical Physics News on Phys.org
Filip Larsen
Gold Member

Motion is always relative to something, so in this case I assume you mean to stop the motion of an object relative to the sun at some point near the earth and then want to know if the earth will move around the sun and then come back to this point a year later? If you were to ignore gravity on the object, then the answer would more or less be yes, but if you include gravity then the answer would be no, as the object would fall toward the sun.

LURCH

In fact, the object would fall toward the Sun and miss, which is kind of the definition of an orbit. Your object would be pulled into a very ellipticle orbit, with the highest point being equal to the distance from which it originaly fell, which is the distance from the Sun to the Earth (1 AU). Unless it made a close pass by Venus or Mercury, or had some other outside force change its orbit, it would continue going in close to the Sun and back out to where the Earth orbits untill it eventually gets to Earth's orbit at the same time Earth is passing through that point in its orbit. Then, of course, it would hit Earth (or Earth would hit it).

Filip Larsen
Gold Member

In fact, the object would fall toward the Sun and miss, which is kind of the definition of an orbit. Your object would be pulled into a very ellipticle orbit, with the highest point being equal to the distance from which it originaly fell, which is the distance from the Sun to the Earth (1 AU). Unless it made a close pass by Venus or Mercury, or had some other outside force change its orbit, it would continue going in close to the Sun and back out to where the Earth orbits untill it eventually gets to Earth's orbit at the same time Earth is passing through that point in its orbit. Then, of course, it would hit Earth (or Earth would hit it).
Any object that is even a bit slower than earth at earths distance from the sun would be in an orbit with a different orbital time than earth, so after a year it it will not be where earth is. If we assume this special object is put into an orbit where perihelios (closest point to sun) is approximately zero, the period of the object would be around 130 days.

LURCH

So, how many orbits before it would hit Earth?

Filip Larsen
Gold Member

So, how many orbits before it would hit Earth?
Well, after one year the object would have done 2 orbits and will be around 22 days from completing its third. In other words, everything else being equal it would miss earth with 22 days on its third orbit.

Dale
Mentor

By the way, the delta v required to get to the sun is very high, much higher than the delta v required to escape the sun. In that sense, the sun is the most difficult place to reach in the universe. You can get anywhere else with less fuel (ignoring, of course, fancy maneuvers like gravitational slingshot etc).

LURCH