Escape velocity
The launch speed needed to leave a planet and never fall back, v = sqrt(2 G M / R), ignoring air.
Last updated
Analogy
A throw so strong the ball never returns.
Example
v = sqrt(2 x 3.98e14 / 6.37e6)v = 11,200 m/s
In practice
Earth's escape velocity is about 11.2 km/s.
Practice
Flashcards
- What is Earth's escape velocity?About 11.2 km/s.
Questions people ask
Is escape velocity the speed rockets must reach?
Not exactly. It applies to a single launch at high speed, ignoring air. Rockets keep their engines on and climb gradually, so they never need 11.2 km/s at ground level. They do need enough total energy, and orbit takes even more energy than just climbing.
Why is a black hole's escape velocity special?
A black hole is so dense that its escape velocity at the surface called the event horizon exceeds the speed of light. Nothing can travel faster than light, so nothing, including light, gets out once inside. The formula is the same, but with extreme mass squeezed into a small radius.