Poetry uses forms and conventions to suggest differential interpretation to words, or to evoke emotive responses. Devices such as assonance, alliteration, onomatopoeia and rhythm are sometimes used to achieve musical or incantatory effects.
The average speed of an object tells you the (average) rate at which it covers distance. If a car's average speed is 65 miles per hour, this means that the car's position will change (on the average) by 65 miles each hour.
Mach number (Ma or M) is the speed of an object moving in air, divided by the speed of sound at that particular conditions, including temperature and pressure. At Standard Sea Level and temperature 15 degrees Celsius, the speed of sound is 761.2 miles per hour (mph) = 340.3 meters per second (m/s) = 1225 km/h = 1116 foot per second (ft/s) = 661.5 knots (kn, kt or kts).