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The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. More simply, the speed of sound is how fast vibrations travel. At 20 °C (68 °F), the speed of sound in air, is about 343 m/s (1,125 ft/s; 1,235 km/h; 767 mph; 667 kn), or 1 km in 2.91 s or one mile in 4.69 s.
Assuming an individual can maintain a speed on the flat of 5 km/h, the route will take 6 hours and 34 minutes. The simplicity of this approach is that the time taken can be easily adjusted for an individual's own (chosen) speed on the flat; at 8 km/h (flat speed) the route will take 4 hours and 6 minutes.
Hull speed or displacement speed is the speed at which the wavelength of a vessel's bow wave is equal to the waterline length of the vessel. As boat speed increases from rest, the wavelength of the bow wave increases, and usually its crest-to-trough dimension (height) increases as well. When hull speed is exceeded, a vessel in displacement mode ...
< 1 mph < 1 km/h 0–0.2 m/s: 0 ft 0 m Sea like a mirror Smoke rises vertically 1 Light air 1–3 knots 1–3 mph 1–5 km/h 0.3–1.5 m/s 0–1 ft 0–0.3 m Ripples with appearance of scales are formed, without foam crests Direction shown by smoke drift but not by wind vanes 2 Light breeze 4–6 knots 4–7 mph 6–11 km/h 1.6–3.3 m/s
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]
The scalar absolute value of velocity is called speed, being a coherent derived unit whose quantity is measured in the SI (metric system) as metres per second (m/s or m⋅s −1). For example, "5 metres per second" is a scalar, whereas "5 metres per second east" is a vector.
A 30 mph speed limit reminder road sign. Used when there is insufficient street lighting for a road to legally have an automatic 30 mph speed limit. In the UK Highway Code for England, Scotland and Northern Ireland, a built-up area is a settled area in which the speed limit of a road is automatically 30 mph (48 km/h). In Wales it's 20 mph (32 ...
d MT = braking distance, m (ft) V = design speed, km/h (mph) a = deceleration rate, m/s 2 (ft/s 2) Actual braking distances are affected by the vehicle type and condition, the incline of the road, the available traction, and numerous other factors. A deceleration rate of 3.4 m/s 2 (11.2 ft/s 2) is used to determine stopping sight distance. [6]