Speed of Light to Foot per Second

No object with mass can reach or exceed c — it would require infinite energy. However, there are phenomena that appear to exceed c without violating physics: the expansion of the universe (space itself stretches), quantum entanglement (no information is transmitted), and phase velocity in certain media. Tachyons — hypothetical faster-than-light particles — have never been detected and would violate causality if they existed.

It is exactly that value by definition — in 1983, the meter was redefined as the distance light travels in 1/299,792,458 of a second. The specific number came from fixing c as exact and inheriting the historical length of the meter from the earlier platinum-iridium prototype. If the meter had been defined differently, c would have been a different exact integer.

About 8 minutes and 20 seconds on average (Earth's orbit is elliptical, so the range is 8m 10s to 8m 27s). Light from the Moon takes 1.3 seconds. From Jupiter at closest approach, about 35 minutes. From the nearest star (Proxima Centauri), 4.24 years. The observable universe is about 46 billion light-years in radius — meaning the light we see from its edge left over 13 billion years ago.

According to special relativity, time dilates for an object moving near c relative to an observer. At 99% of c, time passes about 7 times slower for the traveller compared to a stationary observer. At 99.9999% of c, the factor is about 707. GPS satellites need relativistic corrections (both special and general relativity) applied constantly — without them, GPS would accumulate errors of roughly 10 km per day.

Special relativity predicts several bizarre visual effects. Stars ahead of you would blueshift into ultraviolet and eventually X-rays, while stars behind would redshift into radio invisibility. Aberration would compress the entire sky into a bright ring ahead of you — a phenomenon called relativistic beaming. Time dilation means a trip to Proxima Centauri (4.24 light-years) would feel instantaneous to you at exactly c, though 4.24 years would pass on Earth. Of course, only massless particles can actually reach c — anything with mass would need infinite energy to get there.

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.