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For example, for visible light, the refractive index of glass is typically around 1.5, meaning that light in glass travels at c / 1.5 ≈ 200 000 km/s (124 000 mi/s); the refractive index of air for visible light is about 1.0003, so the speed of light in air is about 90 km/s (56 mi/s) slower than c.
≈ 340 m/s in air at sea level ≈ 295 m/s in air at jet altitudes metre per second (SI unit) m/s ≡ 1 m/s = 1 m/s mile per hour: mph ≡ 1 mi/h = 0.447 04 m/s: mile per minute: mpm ≡ 1 mi/min = 26.8224 m/s: mile per second: mps ≡ 1 mi/s = 1 609.344 m/s: speed of light in vacuum: c: ≡ 299 792 458 m/s = 299 792 458 m/s: speed of sound in ...
using SI units of meters for , hertz (s −1) for , and meters per second (m⋅s −1) for , (where c=299 792 458 m/s in vacuum, ≈ 300 000 km/s) For typical radio applications, it is common to find d {\displaystyle d} measured in kilometers and f {\displaystyle f} in gigahertz , in which case the FSPL equation becomes
Another example: when the speed of light (exactly 299 792 458 m/s [18] by the definition of the meter) is expressed as 3.00 × 10 8 m/s or 3.00 × 10 5 km/s then it is clear that it is between 299 500 km/s and 300 500 km/s, but when using 300 × 10 6 m/s, or 300 × 10 3 km/s, 300 000 km/s, or the unusual but short 300 Mm/s, this is not clear.
This definition fixed the speed of light in vacuum at exactly 299 792 458 metres per second [121] (≈ 300 000 km/s or ≈1.079 billion km/hour [123]). An intended by-product of the 17th CGPM's definition was that it enabled scientists to compare lasers accurately using frequency, resulting in wavelengths with one-fifth the uncertainty involved ...
Low Earth orbit. A view from the International Space Station in a low Earth orbit (LEO) at about 400 km (250 mi), with yellow-green airglow visible at Earth's horizon, where roughly at an altitude of 100 km (62 mi) the boundary between Earth and outer space lies and flying speeds reach orbital velocities. A low Earth orbit (LEO) is an orbit ...
Launch to LEO—this not only requires an increase of velocity from 0 to 7.8 km/s, but also typically 1.5–2 km/s for atmospheric drag and gravity drag [citation needed] Re-entry from LEO—the delta-v required is the orbital maneuvering burn to lower perigee into the atmosphere, atmospheric drag takes care of the rest.
Because the speed of light is a large number in everyday units (approximately 300 000 km/s or 186 000 mi/s), the formula implies that a small amount of "rest mass", measured when the system is at rest, corresponds to an enormous amount of energy, which is independent of the composition of the matter.