Thread: Ask a Scientist
View Single Post
Old 07.03.2013, 09:50
Kosti's Avatar
Kosti Kosti is offline
Senior Member
Join Date: May 2010
Location: Oranje County
Posts: 488
Groaned at 27 Times in 17 Posts
Thanked 871 Times in 364 Posts
Kosti has a reputation beyond reputeKosti has a reputation beyond reputeKosti has a reputation beyond reputeKosti has a reputation beyond repute
Re: Ask a Scientist

Yes. And the linked articles are quite clear on this. An object could be moving at a minuscule speed relative to earth but still 'escape' as long as that speed is maintained by some additional force.

The key point is that the total energy needed to escape (disregarding air resistance which varies with the square of speed) will be the same regardless of the speed used - just that in the bullet example all that energy is imparted in one bang, so that initial speed must 'contain' the kinetic energy needed, whereas the rocket stores it in the form of potential energy (i.e. fuel) and converts in later to kinetic (i.e. moving) energy.
The total energy needed to escape does go up with time spent escaping the Earths gravitational well, even if you ignore air resistance.

Until the rocket achieves orbital velocity, it will use part of its fuel to push against gravity. This is called a "gravity loss" in calculations for launches.
To launch, its best to apply the highest possible acceleration for the shortest possible time.
Reply With Quote