## Why can't a plane fly slowly and let the Earth pass underneath? (Beginner)

This question has been bothering me for ages. When an airplane is airborne, why does it have to travel when it can just stay put at a safe distance above the earth, wait for the earth to rotate and then land when its destination landing nation is available. For example when traveling from India to Egypt, a plane can just get airborne and stay put at safe distance in the sky for about 6 hours during which time the Earth would have rotated and the plane would be above Egypt.

If you fly in the opposite direction that earth is spinning, basically flying against the spin, the earth is moving toward you with the spin at the speed of 1000 miles per hour. Assuming the plane is flying at 500 mph on its own, why are you not flying toward your destination at the speed of 1500mph?

The reason an airplane can't just idle and let the ground pass underneath is the same reason as why a ball dropped from a tall tower lands at the base of the tower and not next to it. A plane sitting on the ground is moving with the surface of the Earth, and while it appears to us to be at rest, it is actually moving at around 1,000 miles an hour (the exact value depends on your latitude). When it takes off, it still has speed from sitting on the ground. In order to fly east, the plane increases its speed relative to the surface of the Earth and begins to overtake it. Flying west it decreases its speed relative to the surface of the Earth, and the Earth slips by.

Here's a thought experiment. Imagine three moving walkways with a person standing on each one. Now let the person on the left walkway walk forward in the same direction as the walkway, the person in the center stay standing, and the person on the right walk backward in the opposite direction. All three people are moving in the direction that the walkway is moving, but the two people walking are moving in that direction more quickly and less quickly, respectively, than the person at rest. When the plane is sitting on the ground, it is like the person standing still on the moving walkway. The two people walking in same direction and opposite direction of the walkway are like the plane in air.

#### Laura Spitler

Laura Spitler was a graduate student working with Prof. Jim Cordes. After graduating in 2013, she went on to a postdoctoral fellowship at the Max Planck Institute in Bonn, Germany. She works on a range of projects involving the time variability of radio sources, including pulsars, binary white dwarfs and ETI. In particular she is interested in building digital instruments and developing signal processing techniques that allow one to more easily identify and classify transient sources.