# Jump off earth

Seeing as how the earth rotates, if i go on board a helicopter and lifted off ground, hovering at exactly the same spot without moving for 2 hours, when the chopper lands, will i still be at the same spot? Or would my position have shifted since the earth rotates.

The air the helicopter is on is constantly moving when compared to the rotating earth bellow it. In order to hover, the helicopter has to make constant corrections, which it usually makes with relation to the ground. Don’t forget that the air is rotating too, which is why clouds aren’t rushing by so that any cloud you see now was in China 12 hours ago. OTOH, if you left the atmosphere and entered orbit, you would come back somewhere else.

Similar would be riding a train and hovering an r/c helicopter and landing it inside the train. It would land in the same spot.
However if you were riding outside on top of the train where the atmosphere is not moving along with the train, then no, it would probably land on the tracks after the train was long gone.

“Exactly the same spot?”
With reference to what?
Remember, the Earth is orbiting the Sun at around 18 miles/second, so if your helicopter didn’t move in relation to the center of the Sun, it would end up outside of the atmosphere in a flash.

Also, the sun is orbiting the center of the galaxy, and the galaxy is moving through space, too…etc,etc.

Standing still is never an option.

We have to run as fast as we can to stay in the same place.

Using the center of our galaxy as a starting point, can our current speed be calculated?

Ludicrous Speed!

220km per second, apparently. Or, what DrFidelius said.

Your mom

So using that as a base, where would our hovering helicopter be in two hours if it could ignore atmospheric drag, gravity and all other factors that cause it to “go with the flow”?

Inertia is conserved. Hovering above the Earth you retain all of the directional inertia you had before you hovered.

If you didn’t, everything in the Universe would have been destroyed long ago.

Monty Python’s Galaxy Song
Just remember that you’re standing on a planet that’s evolving
And revolving at nine hundred miles an hour,
That’s orbiting at nineteen miles a second, so it’s reckoned,
A sun that is the source of all our power.
The sun and you and me and all the stars that we can see
Are moving at a million miles a day
In an outer spiral arm, at forty thousand miles an hour,
Of the galaxy we call the ‘Milky Way’.

Even worse than that as we’re moving at an amazing 370 kilometers per second relative to the cosmic microwave background.

As Chimera said, it would still be travelling at the same speed as Earth. The hovering force doesn’t cancel out all its existing momentum. It’s not the fact that the atmosphere is moving with the Earth that keeps the helicopter moving - with no atmosphere, the helicopter (or rocket as it would have to be now) would still stay in one place relative to the Earth, thanks to its horizontal momentum.

In the example of a toy helicopter taking off from the roof of a moving train, of course it will get blown backwards (relative to the train) by the rush of wind, but that’s purely because the train is moving relative to the Earth (and thus atmosphere). If there were no atmosphere, an object launched “straight up” from atop a moving train would land back in the same spot on the train, assuming the train kept going in a straight line at the same speed.

My Mom only thinks she’s the center of the Universe…

I don’t think that’s true, because you are not accounting for the Coriolis effect. The train isn’t moving in a straight line, as the Earth is not flat. Send the object high enough, and it won’t land in the same spot.

Yo mama’s so fat she gravitationally affects galaxies in the local supercluster.

My train was travelling along a flat plane in space.

That’s the best train related excuse I’ve heard since “leaves on the line”.

An object sitting on the ground is actually zooming through space at high speeds. It doesn’t stay on the ground because of friction, or because the wind is still, it stays on the ground because it is moving through space at almost exactly the same speed and direction as the ground.

Attach a helicoptor rotor to the object and have it hover a few feet off the ground, and it is still moving through space at almost exactly the same speed and direction as the ground. It isn’t going to stay stationary while the ground rotates away underneath, because you’d have to expend a large amount of energy to stop the object moving. An object in motion stays in motion unless acted upon by an outside force.

In order for a helicopter to rise up and stay stationary as the earth rotates underneath it, you’d have to use a lot of energy to kill the helicoter’s velocity relative to the earth, then when you want to land you’d have to use a lot of energy to speed back up to the earth’s velocity–either that or use the motion of the passing atmosphere to speed you back up, or friction with the earth (this is what scientists call “crashing”). And simpler way to look at this process of killing your velocity relative to the earth is that you expend energy to move your helicopter.

We’re used to the idea that things stop moving on their own because here on Earth objects experience a lot of friction from both the air and the ground. Throw a ball, and the air slows it down, and then it hits the ground and slows down, and pretty soon it stops relative to the Earth. But it didn’t stop because it’s natural for things to stop moving, it stopped because outside forces acted on the ball.

But gravity curves spacetime…