QUESTION #167

# Is the rotation of the earth considered the initial kinetic energy for a rocket before take-off?

Yes, a rocket sitting on its launching pad on Earth has an eastward velocity due to the rotation of the Earth. That is why almost all rockets take an easterly trajectory after a vertical launch. (Exceptions would be satellites designed to cover the largest portion of the Earth's surface, placed in a polar orbit to allow the Earth to rotate beneath them.)

The maximum eastern velocity available is at the equator, where a point on the surface travels about 25,000 miles in 24 hours, or over 1000 miles per hour. As you move north or south of the equator, the circle traveled each day, and therefore the speed, becomes smaller until it becomes zero at the poles. This was a prime factor in locating Cape Canaveral as far south, in Florida, as it was. The velocity already imparted by Earth's rotation is that much less needed by the rocket's own fuel to attain the necessary orbital speed.

Interplanetary vehicles travelling to the outer planets can also take advantage of the Earth's orbital velocity around the Sun (about 18 miles per second), while those travelling to the inner planets must reduce the orbital speed imparted by the Earth to 'fall' toward a closer orbit.
Answered by: Paul Walorski, B.A. Physics, Part-time Physics Instructor