What is Escape speed?
'''Escape speed''' is the initial [[speed]] that something would need to completely escape the [[gravity]] of a large body, like a [[star]] or a [[planet]] (such as the [[Earth]]), by mere [[inertia]]. If a ball is thrown upwards while standing on the ground, the ball will reach a certain height (the faster thrown - the higher) and fall back down. But imagine if the ball is thrown fast enough that it ''never'' falls back down, and instead travels into [[Space (physics)|space]] farther and farther away from the Earth. The minimum speed at which this could happen is called the escape speed. The escape speed at the surface of the Earth is 11.2 [[kilometer]]s per [[second]] (or 6.96 [[mile]]s per second), assuming there is no [[Drag (physics)|drag]]. This is, of course, a very high speed compared to how fast a ball can be thrown. Even a [[bullet]] shot into the sky will fall back down, because its initial speed of nearly 1 kilometer per second (or 0.621 miles per second) is far from escape speed. [[Spacecraft]] starting from the surface of Earth has a zero initial speed. But, if it has enough [[fuel]], it may be permanently [[Acceleration|accelerated]] by its [[Rocket engine|engine]] until it reaches escape speed. Then it will travel into space even after the engine is shut off. ==References== *{{cite book |author1=Roger R. Bate |author2=Donald D. Mueller |author3=Jerry E. White |title=Fundamentals of astrodynamics |url=https://archive.org/details/fundamentalsofas00bate |publisher=[[Dover Publications]] |location=New York |year=1971 |isbn=978-0-486-60061-1 |oclc= |doi=}} {{reflist}} [[Category:Astrophysics]] {{physics-stub}}