Foot per Second to Mile per Hour

A professional golfer's driver launches the ball at roughly 250 ft/s (170 mph). An amateur averages about 190–220 ft/s. The PGA Tour record ball speed is around 330 ft/s (225 mph), set by long-drive competitors using specialised equipment. For comparison, a tennis serve reaches about 180 ft/s and a baseball pitch about 150 ft/s — making a driven golf ball one of the fastest objects in non-motorised sport.

A skydiver in a stable spread-eagle position reaches terminal velocity at approximately 120 mph (176 ft/s) after about 10 seconds of freefall. In a head-down dive position, terminal velocity can reach 200+ mph (293+ ft/s). With a deployed parachute, descent slows to about 10–17 ft/s (7–12 mph) for a safe landing.

Vertical speed indicators in aircraft (VSI) use feet per minute because typical climb and descent rates produce sensible numbers — a commercial aircraft climbs at 1,500–2,500 ft/min, and descends at 300–500 ft/min for approach. In ft/s these would be 25–42 and 5–8 respectively — workable, but ft/min produces rounder pilot-friendly numbers for the ranges encountered.

Foot per second squared (ft/s²) is the imperial unit of acceleration. Standard gravitational acceleration is 32.174 ft/s² — meaning a falling object gains 32 ft/s of speed every second. This is used in US aerospace and artillery calculations. Engineers must be careful not to confuse ft/s (speed) with ft/s² (acceleration), as the units look similar but represent entirely different physical quantities.

One knot is approximately 1.6878 ft/s (or 1 nautical mile per hour). This means 100 knots is about 169 ft/s. Aircraft airspeed is measured in knots by international convention, but US military aircraft radar tracks and some engineering documents also express speeds in ft/s for compatibility with imperial-unit weapon system specifications.

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.