Kilometer per Second to Mile per Hour

Earth orbits the Sun at an average of about 29.8 km/s (107,000 km/h). This speed varies slightly because Earth's orbit is elliptical — it moves fastest in January (perihelion) at 30.3 km/s and slowest in July (aphelion) at 29.3 km/s. You're traveling at this speed right now relative to the Sun.

Escape velocity is the minimum speed needed to leave a body's gravitational influence without further propulsion. From Earth's surface it's 11.2 km/s. From the Moon it's 2.4 km/s. From the Sun's surface it's 617.5 km/s. The Voyager 1 spacecraft left Earth's sphere of influence at about 16.6 km/s.

Primary (P) waves travel at 5–8 km/s through Earth's crust, reaching 13 km/s in the mantle and core. Secondary (S) waves travel at roughly 60% of P-wave speed. This speed difference is why seismologists can calculate earthquake distance — the gap between the P and S wave arrival times reveals how far the sensor is from the epicenter.

Meteoroids enter Earth's atmosphere at 11–72 km/s, depending on whether they're moving with or against Earth's orbital direction. The friction at these speeds heats them to incandescence — the streak of light visible as a 'shooting star'. Most disintegrate completely above 80 km altitude. The upper bound of 72 km/s is the sum of Earth's orbital speed plus the body's own velocity.

A typical high-powered rifle round (e.g. 7.62×51mm NATO) travels at about 0.85 km/s (850 m/s or 3,060 km/h). Purpose-built anti-materiel rifles reach ~1.0 km/s. Railgun projectiles in military experiments have exceeded 3 km/s. All of these are far below orbital speed — getting to orbit requires speed, not just height.

The UK officially began metrication in 1965, but road signage was exempted to avoid the enormous cost of replacing signs. The 1969 decision to postpone road metric conversion was intended as temporary, but no subsequent government has prioritized the change. A 2021 review considered reverting the post-Brexit UK to imperial in other areas too, but road signs remain mph by law (The Traffic Signs Regulations and General Directions).

The Saffir-Simpson Scale defines a hurricane as sustained winds of 74 mph or more. Category 5 begins at 157 mph. The strongest recorded tropical cyclone was Typhoon Tip (1979) with 190 mph sustained winds. For context, a Category 1 hurricane at 74 mph will rip roof shingles and topple shallow-rooted trees; Category 5 causes catastrophic structural damage.

Aroldis Chapman set the official MLB record with a pitch recorded at 105.1 mph in 2010. The ball travels the 60.5 ft (18.4 m) from mound to plate in about 0.39 seconds — leaving the batter about 0.15 seconds to react after recognising the pitch type. For comparison, a tennis serve record is 163.7 mph (Sam Groth, 2012).

60 mph is 96.56 km/h — close but not the same. The actual crossover is at 62.137 mph = 100 km/h. Many countries set urban motorway limits at 100 km/h partly because it approximates a round 60 mph for visitors from mph-using countries. The error is about 3.5%, negligible for driving but meaningful for engineering calculations.

The 55 mph national speed limit was set in 1974 during the oil crisis — Congress chose it to maximize fuel economy, not because it was a round number. When the federal mandate was lifted in 1995, states picked 65, 70, or 75 mph based on traffic engineering studies of the 85th-percentile speed drivers naturally travel on a given road. Texas has the highest posted limit at 85 mph on a toll road near Austin. The seemingly arbitrary numbers are actually data-driven safety thresholds, not aesthetic choices.