How do things stay in orbit with gravitational acceleration?

[SaturnVee]

If an orbit is just a substantial horizontal velocity, and it is still technically a falling object, shouldn't it be susceptible to downwards gravitational acceleration and in turn need to increase its horizontal velocity to maintain a stable orbit? Or is there a force stopping the given object from falling at an increased rate?

[Psycix]

A simple way to look at it is:

You do not gain vertical acceleration because centrifugal forces (upward) cancel out the gravitational forces (downward).

Another way to look at it is:

As you fall over the planet, gravity makes you gain downward velocity, but lose horizontal velocity. In the end, your speed is the same (in a circular orbit), but you are simply going in a different direction. The reason you do not hit the ground, is because you moved OVER the planet (or the planet under you) and what first was "down" is now a different direction. The speed gained on one side cancels out the speed gained on the opposite side, causing you to travel in in an circular (or ellipse-shaped) path.

Make sure you imagine the situation from the correct frame of reference!

[SaturnVee]

A simple way to look at it is:

You do not gain vertical acceleration because centrifugal forces (upward) cancel out the gravitational forces (downward).

Another way to look at it is:

As you fall over the planet, gravity makes you gain downward velocity, but lose horizontal velocity. In the end, your speed is the same (in a circular orbit), but you are simply going in a different direction. The reason you do not hit the ground, is because you moved OVER the planet (or the planet under you) and what first was "down" is now a different direction. The speed gained on one side cancels out the speed gained on the opposite side, causing you to travel in in an circular (or ellipse-shaped) path.

Make sure you imagine the situation from the correct frame of reference!

That helped a lot, thanks man!

[lajoswinkler]

Or you could look at it from an energy conservation standpoint.

http://physics.ucsc.edu/~josh/6A/book/gravity/node15.html

Here's an interesting fact. It's one of the things that works with gravitation only. If the objects were charged and the force was electrical, orbiting would emit energy in the form of photons because the body is constantly accelerating (although the scalar stays the same, the vector changes its value, so it's some kind of acceleration) and the body would lose height, eventually colliding with the main body. It was a huge problem in the earlier days of atomic theory because electrons were thought to be orbiting the nucleus, and should therefore crash into the nucleus.

Bohr postulated "they orbit and they don't lose energy" just to make his atomic model. It was later discovered that electrons in atoms are standing waves called orbitals, so they don't lose energy.