Cosmic Velocity - Second to Knot

The second cosmic velocity (Earth's escape velocity) is approximately 11,200 m/s (11.2 km/s), the minimum speed to escape Earth's gravity completely.

v₂ = √(2GM/r) = √2 × v₁ ≈ 11.2 km/s. Exactly √2 times the first cosmic velocity.

To km/h: × 3,600. To mph: × 25,000. 11.2 km/s = 40,320 km/h = 25,053 mph.

Moon missions, Mars missions, deep space probes (Voyager, New Horizons), and any mission leaving Earth's gravity well.

Apollo missions: ~11.2 km/s. Voyager probes: exceeded v₂ to leave solar system. New Horizons: launched at record 16.26 km/s (fastest ever from Earth).

Thinking you need this speed everywhere — you only need it at launch. In space, much less Δv is needed.

~11 km/s to escape Earth. √2 × orbital velocity. Remember: orbit ≈ 8 km/s, escape ≈ 11 km/s.

A knot is one nautical mile per hour, where a nautical mile equals exactly 1,852 meters. It's the standard speed unit in maritime and aviation contexts.

1 knot = 1 nautical mile/hour = 1,852 m/h = 1.852 km/h = 0.514 m/s. One nautical mile = 1,852 meters exactly.

To km/h: × 1.852. To mph: × 1.151. To m/s: × 0.514. To ft/s: × 1.688.

Ship cruising speeds (cruise ships: 20–25 knots), aircraft speeds (Boeing 747: 490 knots cruise), wind speed in aviation weather reports (METAR), and sailing.

Fastest ship: 60+ knots (naval vessels). Blue whale swim: 5–20 knots. Jet stream winds: 80–140 knots. Hurricane-force winds: 64+ knots.

Saying 'knots per hour' — incorrect! A knot already includes 'per hour.' Just say 'knots.' Also, confusing nautical and statute miles.

1 knot ≈ 1.85 km/h. Roughly: 10 knots ≈ 20 km/h. Remember: knots are for sea and sky, km/h and mph are for land.