Imagine you're inside an elevator, and the cable breaks and it starts falling. This elevator doesn't have any of the usual safety systems to stop a freefall. In fact, just to make it worse, all the air has been pumped out of the elevator shaft, and it's also set up so there is no friction to slow it down.

So the elevator keeps falling, and accelerating as it falls.

Inside the elevator, you're also falling and accelerating at exactly the same rate.

You're going to start floating around inside the elevator, because it's falling, and you're falling, and you're both falling exactly the same. To you inside the elevator, it won't look like the elevator is moving at all. You can just float around inside it.

Only problem is when you hit the ground.

How can we avoid that? Take the elevator car out of its shaft, but keep it in a near-vacuum so there's no air resistance. Now give it a really hard push sideways. It's still going to fall, just like before, but if you get it going fast enough sideways, then by the time it would have fallen to the ground, the ground will have dropped away too! Because the Earth is round.

So now you won't hit the ground any more. Get that sideways speed just right, and as your elevator car falls, the ground will drop away (because of the curvature of the earth) by exactly the same amount.

It's like magic. The elevator car is still falling - you can't avoid that. After all, the Earth's gravity keeps pulling it down. And you're still falling too. But just like before, you and the elevator are falling at the same rate, so you can keep floating around inside it. Or outside it if you like.

And since the surface of the round Earth is also getting out of your way as you fall, you can keep doing this as long as you like. You're in orbit!