# Escape velocity earth confusion

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1. Apr 14, 2015

### AakashPandita

Namaste
If escape velocity on earth is 11 km/s and velocity of earth is 30 km/s how is that the atmosphere doesn't escape the pull of earth.
Is the escape velocity with reference to earth ? I don't think so because when finding the formula we add kinetic and potential energy and then equate to zero. If it is not then doesn't everything on earth has velocity greater than escape velocity...

2. Apr 14, 2015

### rcgldr

The escape velocity on earth is relative to the earth. In the outer fringes of the atmosphere, a very tiny percentage of molecules will randomly end up with >= escape velocity. Escape velocity from the solar system, is relative to the Sun (with some effect from orbiting planets). There are a few satellites that have exceeded escape velocity from the solar system. A list of them from wiki:

http://en.wikipedia.org/wiki/List_of_artificial_objects_escaping_from_the_Solar_System

3. Apr 14, 2015

### AakashPandita

If the escape velocity is relative to earth then why is it that( i read in my book) that projectiles are projected in the direction of rotation of earth ?

4. Apr 14, 2015

### A.T.

It's relative to the Earth centered non-rotating frame.

Last edited: Apr 14, 2015
5. Apr 14, 2015

### rcgldr

At the equator, the surface speed of the earth relative to it's center of mass is about 0.464 km/s. As posted by A.T., the escape velocity from the earth is not affected by the earth rotation, but by launching a rocket to the east at the equator the rocket would start with 0.464 km/s speed relative to the center of mass of the earth, reducing the fuel it would need to reach orbital or escape velocity speeds.

6. Apr 14, 2015

### AakashPandita

Thanks. It makes sense to me now,