The relationship between speed, distance and time of a moving object is given by:
where v is the speed, d is the distance that the object has moved, and t is the time being spent.
What is the average speed if it takes 4 hours to walk 16 miles?
The distance is d = 16 miles, the time being spent is t = 4 h, and the speed is:
Notice that the unit mph actually is expressed in the formula: miles divided by hours (miles per hour).
Conversion between units
You often need to convert to other units than those that are given to you.
A car is driving 5280 yards in 3 minutes.
What is the average speed of the car in miles per hour?
You convert the distance to miles first.
Since 1 mile is equal to 1760 yards, the distance in miles is:
Then you convert the time to hours:
Since 1 hour is equal to 60 minutes, the time in hours is:
The speed in miles per hour is then:
The conversion factor
If you want to convert from one speed unit to another, the first thing you do is to calculate the conversion factor, that is, the number you multiply the original unit by in order to get the new unit.
You want to convert 60 mph to ft/s (feet per second)
First you must calculate how many seconds there are in an hour.
and then how many feet a mile is:
now you can calculate the conversion factor:
Rand finally you can convert the unit to fps by multiplying it by the conversion factor:
Table of conversion factors of speed units
It’s much easier to do the conversion between units when you can find the conversion factors in a table like this one:
|from / to||km/t||m/t||m/s||cm/M||Mach||Knot||mph|
km/t = kilometers per hour
m/t = Meters per hour
m/s = Meters per second (SI unit)
cm/M = Centimeter per minute
Mach = the speed of sound, which is 343.2 meters per second (1,126 ft/s)
(Mach is pronounced “mark”. The unit is written in front of the value. Mach 2 is, for instance, twice the speed of sound)
Knot = nautical miles per hour
mph = Miles per hour
How to use the table
If you, for instance, want to convert a speed from ft/s to mph, you find the number in the row named ft/s and the column named mph.
The number is 0,681818, which means that 1 ft/s = 0,681818 mph.
So when you want to convert a speed given in ft/s, you multiply it by 0,681818 in order to get it in mph.