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T 25 is 298.15 K (= 25 °C = 77 °F), giving a value of 346.1 m/s (= 1 135.6 ft/s = 1246 km/h = 774.3 mph = 672.8 kn). In fact, assuming an ideal gas , the speed of sound c depends on temperature and composition only, not on the pressure or density (since these change in lockstep for a given temperature and cancel out).
4–7 mph 6–11 km/h 1.6–3.3 m/s 1–2 ft 0.3–0.6 m Small wavelets still short but more pronounced; crests have a glassy appearance but do not break Wind felt on face; leaves rustle; wind vane moved by wind 3 Gentle breeze 7–10 knots 8–12 mph 12–19 km/h 3.4–5.4 m/s 2–4 ft 0.6–1.2 m
The original Naismith's rule from 1892 says that one should allow one hour per three miles on the map and an additional hour per 2000 feet of ascent. [1] [4] It is included in the last sentence of his report from a trip. [1] [8] Today it is formulated in many ways. Naismith's 1 h / 3 mi + 1 h / 2000 ft can be replaced by:
If the speed of sound is not known, Mach number may be determined by measuring the various air pressures (static and dynamic) and using the following formula that is derived from Bernoulli's equation for Mach numbers less than 1.0. Assuming air to be an ideal gas, the formula to compute Mach number in a subsonic compressible flow is: [8]
A 420-gram (15 oz) football (FIFA specified weight for outdoor size 5) kicked to a speed of 8.6 km/h (5.3 mph). 0.42 38 16 The momentum of the famous football kick of the Brazilian player Roberto Carlos in the match against France in 1997. The football had a speed of 137 km/h (85 mph), making it one of the hardest kicks measured. 1300: 10 13 000
DIN 66036 defines one metric horsepower (Pferdestärke, or PS) as the power to raise a mass of 75 kilograms against the Earth's gravitational force over a distance of one metre in one second: [17] 75 kg × 9.80665 m/s 2 × 1 m / 1 s = 75 kgf⋅m/s = 1 PS. This is equivalent to 735.49875 W, or 98.6% of an imperial horsepower.
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.
Airspeed is commonly given in knots (kn). Since 2010, the International Civil Aviation Organization (ICAO) recommends using kilometers per hour (km/h) for airspeed (and meters per second for wind speed on runways), but allows using the de facto standard of knots, and has no set date on when to stop.