Velocity Converter

The Parker Solar Probe reached a record speed of about 192 km/s = 692,000 km/h at its closest solar approach in late 2024, making it the fastest human-made object. This corresponds to about 0.064% of the speed of light. NASA's Helios probes reached 70.2 km/s in the 1970s. By comparison, Voyager 1 travels at about 17 km/s relative to the Sun.

The speed of sound decreases with temperature: v_sound = 331.3 × √(T/273.15) m/s, where T is in Kelvin. At 11,000 m (commercial cruising altitude) where T ≈ 217 K, Mach 1 = 295 m/s = 1062 km/h, compared to 343 m/s at 20°C sea level. Commercial aircraft cruise at Mach 0.82-0.85 = 854-888 km/h true airspeed at cruise altitude.

No information or massive object can travel faster than c. However, the phase velocity of light in a medium can exceed c (but carries no information). Quantum entanglement correlations appear instantaneous but cannot transmit information faster than c. Galaxy recession velocities can exceed c in an expanding universe — but these are not motion through space, they are expansion of space itself, which is not bounded by special relativity.

Escape velocity v_esc = √(2GM/R): Moon = 2.38 km/s; Earth = 11.19 km/s; Mars = 5.03 km/s; Jupiter = 59.5 km/s; Sun = 617.5 km/s from its surface; neutron star surface ≈ 0.4-0.5 c; black hole event horizon = c (by definition). The asteroid Vesta has escape velocity of only 0.36 km/s — a strong throw on Earth would escape Vesta.

Stars in the Milky Way orbit the galactic center at typically 200-250 km/s. The Sun orbits at 220 km/s (0.073% of c) at radius 8.2 kpc, with an orbital period of about 225 million years (one galactic year). The Milky Way itself moves at about 600 km/s relative to the Cosmic Microwave Background rest frame — this bulk motion is sometimes called our peculiar velocity relative to the CMB.

The International Space Station orbits at approximately 7.66 km/s = 27,600 km/h = 17,100 mph at altitude ~408 km. At this speed, it completes one orbit every 92.68 minutes, experiencing about 15.5 sunrises per day. The relativistic time dilation at ISS speed (7.66/299,792 km/s = 2.56 × 10⁻⁵ c) causes clocks on ISS to run slow by about 7 microseconds per day compared to Earth.

The drift velocity of electrons in a copper wire carrying typical household current (1 A in 2 mm² wire) is only about 0.07 mm/s — astonishingly slow! The electrical signal propagates at 50-90% of c because it is an electromagnetic wave, not the actual motion of electrons. Electrons in a wire undergo random thermal motion at ~10⁶ m/s but drift only ~0.1 mm/s in the current direction.

Using the Maxwell-Boltzmann distribution at 300 K: nitrogen (28 u) has mean speed v = √(8kT/πm) = 474 m/s and rms speed = 517 m/s. Lighter hydrogen molecules (2 u) move at 1770 m/s mean. These random molecular speeds explain the speed of sound (~343 m/s for N₂-dominated air) and the distribution of atmospheric escape: hydrogen can occasionally achieve Earth escape velocity (11.2 km/s) through the high-energy tail of the Maxwellian distribution.

Terminal velocity is reached when air drag equals gravitational force: v_t = √(2mg/CdρA). For a person in spread-eagle position: m ≈ 80 kg, Cd ≈ 1.0, A ≈ 0.7 m², ρ_air ≈ 1.2 kg/m³ → v_t ≈ 56 m/s = 200 km/h. In head-down position (skydiving): Cd ≈ 0.7, A ≈ 0.2 m² → v_t ≈ 90 m/s = 324 km/h. The record is 1357 km/h (Felix Baumgartner, 2012), achieved in near-vacuum where drag is negligible.