Conversion from 4 Feet per second to Meters per second

Information about the Foot per second (fps)

The foot per second is a unit of speed equal to one foot travelled in one second. Its symbol is fps, sometimes written ft/s. It is the imperial and US customary counterpart of the metre per second, and it appears wherever a short-duration speed is measured in a country that works in feet.

Ballistics is its main home. Muzzle velocities are quoted in feet per second almost universally in English-language sources, so a rifle cartridge at 3000 feet per second or a subsonic pistol round below 1100 are standard descriptions among shooters. The threshold matters because the speed of sound at sea level is about 1125 feet per second, and a bullet that crosses it produces a sonic crack that suppressors cannot remove.

American engineering uses it for anything falling, flowing or rotating over short intervals. Acceleration due to gravity is 32.174 feet per second squared, a number as familiar in American textbooks as 9.81 metres per second squared is elsewhere. Fluid velocities in pipes, conveyor speeds and the descent rates on aircraft instruments follow the same convention, though aviation more often uses feet per minute for vertical speed.

Sport measurement in the United States uses it for pitch and swing speeds where a short flight makes miles per hour feel coarse, and film and animation borrow the abbreviation for a different quantity entirely, frames per second, which is a frequency rather than a speed.

Falling bodies gave the unit its place in the classroom. In imperial terms gravity accelerates an object at 32.174 feet per second every second, so a stone dropped from rest is moving at about 32 feet per second after one second and 64 after two, and the height fallen is sixteen feet in the first second. Those round-ish numbers were the staple of American and British physics teaching for a century, and they survive in rules of thumb: a fall from a first-floor window reaches roughly 25 feet per second, and the terminal velocity of a human body in air is about 175. Each of them describes a hazard in the unit the trade already uses.

One foot per second equals 0.3048 metres per second exactly, about 1.09728 kilometres per hour, or about 0.681818 miles per hour.

Information about the Meter per second (m/s)

The metre per second is the SI unit of speed. Its symbol is m/s. It is a derived unit, formed from the base units of length and time, and it is the speed at which an object covers one metre in one second.

Physics uses nothing else. Every equation of motion, every conservation law and every result in mechanics assumes speeds in metres per second, because mixing in an hour or a mile would force conversion factors into formulas that are otherwise clean. The speed of light in vacuum is exactly 299,792,458 metres per second, a defined value since 1983, and that definition is what fixes the length of the metre.

Outside the laboratory the unit is less comfortable. Road speeds in metres per second would be small numbers with awkward decimals, which is why almost every country signs roads in kilometres per hour instead. Where the metre per second does appear in daily life, it is usually because the quantity is short-lived or physical rather than navigational: wind speed in meteorological reports, the speed of sound at about 343 metres per second in air at twenty degrees Celsius, and lift or conveyor speeds in engineering specifications.

Sport uses it for anything measured over a short course. Sprint velocities, swimming splits and ball speeds are often analysed in metres per second even where the published result is in kilometres per hour, because it makes acceleration and stride analysis straightforward.

A handful of speeds in this unit are worth carrying in memory because so much else is measured against them. Sound travels through dry air at about 343 metres per second at room temperature, through water at 1480 and through steel at some 5000, which is why a distant lightning strike is timed at roughly three seconds to the kilometre. Light in vacuum moves at exactly 299,792,458 metres per second, a number now fixed by definition rather than measured, and the metre itself is derived from it. Between those extremes sit the everyday values: a brisk walk is 1.4 metres per second, a motorway car 33, and a passenger jet about 250.

One metre per second equals 3.6 kilometres per hour, about 2.23694 miles per hour, or about 1.94384 knots.