Space
Explainer
Escape velocity: energy, not rockets
To leave Earth without more thrust, you need about 11.2 km/s.
Quick check · tap an answer to continue
Lesson notes
Key points
- Escape velocity is the minimum launch speed where kinetic energy exactly cancels gravitational potential energy.
- Setting half m v² equal to G M m over r gives a speed independent of the object's own mass.
- For Earth's surface this works out to roughly 11.2 kilometres per second.
- It is exactly √2 times circular orbital speed at the same radius, a common exam connection.
Definitions
- Escape velocity
- Minimum speed for an unpowered object to reach infinity with zero remaining speed.
Takeaway: v_esc = √(2GM/r), independent of the escaping mass.
Quick check: Doubling a probe's mass changes escape velocity by?
- Doubles it
- Halves it
- No change
Escape velocityEnergy balanceEarth's value√2 relation
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