How does moving horizontally prevent satellites from falling towards earth?


If I was on a satellite, and I pushed an apple towards earth, would it stop falling and level out?

And if I was on a satellite and pushed an apple in the opposite direction at the same speed I was travelling
(net speed = 0), would it start falling towards earth?

In: Physics

A bit like how swinging an unwound yoyo round lets it travel in a big circle rather than just falling down. It’s got sideways momentum and a constant force which makes it go in a circle (the tension in the string doing the same job as gravity on the satellite).


Stand on a mountain and throw a ball. It moves horizontally to the surface of the Earth, but gravity pulls out down so it eventually his the ground.

Now imagine a really tall mountain and you throw the ball really fast. It moves away from the Earth because you are on the high mountain, but gravity pulls it back towards the Earth as well.

There is a specific velocity where these forces balance out and the ball “falls” all the way around the Earth and just keeps falling. That’s a satellite.

It’s not just the horizontal motion. The horizontal motion is a result of the upward motion and the pull of gravity.

Have you ever seen ski jumping? They go down a sloping track and hit a little ramp at the end. They reach 100 meters or so before landing not because they go high, but because the ground slopes away underneath so they fly down almost parallel to the slope.

Translate that to the slope being the curvature of the Earth and the speed and launch ramp being the rocket. Go fast enough and the Earth curves away as fast as the satellite falls towards it.

Orbital mechanics are counterintuitive. If you are in orbit things don’t move in the direction you push them.

If you push something “down” it will instead move “forward” ahead of you in orbit, you need to push it “back” to get the object to move “down”.

So yes pushing the apple “back”, i.e. slowing it down will make it go lower and lower.

The trick with orbits is not that you are somehow preventing the orbiting object from falling down, it is to move so fast that as you fall down you keep missing the ground.

“Horizontally” is an object that not just flat-earthers have trouble with. In every day life we keep treating the idea of “horizontally” as a straight line. Obviously in reality the earth is not flat and on a big enough scale horizontally ends up meaning a curved path rather than a straight one.

If you are in orbit and try to move not parallel to the ground but on a straight tangent to a curve that is parallel to the ground, you would in theory move away from it.

To imagine that put a ruler on top of a ball. The further you go from the point where the ruler rest upon the ball the greater the distance between the ruler and the surface of the ball.

So moving in a straight line while up above the earth actually gets you away from the ground. The earth curves away beneath you is you move straight ahead.

Of course gravity is a thing and as the same time as you move away from the earth you also fall towards it.

When you fall down at the same rate as the earths curves away from you, you keep the same distance from it.

Satellites, like any object that is thrown into the air, are still affected by the force of gravity. They do fall towards the earth, in a sense. The harder you throw an object, the farther it will go before it lands. If you were able to throw it hard enough, and if air resistance didn’t slow it down, it could theoretically fall at the same rate that the earth curved away from it. In a sense, it’s always falling, but the earth is always curving away from it. Satellites don’t experience sufficient resistance from the atmosphere to slow them down enough to fall out of orbit. They can keep flying at a very high horizontal speed and keep “falling” back to earth. Since the earth is round, the earth “falls away” at the same rate, so they stay at the same altitude.