**Knots** is how the speed of aircraft and boats is measured.
Both miles per hour and knots is a speed which is the number of units
of distance that is covered for a certain amount of time.

1 knot = 1 nautical mile per hour = 6076 feet per hour

1 mph =1 mile per hour = 5280 feet per hour

For example, if a train is moving at 50 mph on a track, how would you represent this speed in knots (even though trains are not usually represented in knots)?

To do this problem easily, one can multiply the number of miles
per hour that the train is moving by the number of feet per hour that
= 1 mph. this converts the speed to a distance traveled in one
hour.

That is,

Now, divide that distance by the number of feet in a nautical mile (6076).

- Complete the following chart:

In aerodynamics, speed is also measured by the **Mach number**, which is the
ratio of the speed of the object to the speed of
sound. Mach 1 means that you are traveling at the speed of sound or
661.7 knots, or

How would you determine the speed of sound in mph?

Since

= 4,020,489.2 feet/hr

and

We can say that Mach 1 = 761.5 mph at sea level.

Since the speed of sound varies with the density of air ( or
whatever material it is transmitted through), one needs to determine
the density of the air the aircraft is flying through. To compute
this, we will use the chart shown below, called the **International
Civil Aviation Organization Table, or I.C.A.O.**

Notice as the altitude increased, the density of air decreases as does the speed of sound in knots.

- Using the I.C.A.O. table below, complete the following chart:
- Now complete the following chart:
A text only version of this problem and answer are also available.

Altitude (Feet) |
Density |
Speed of Sound (Knots) |
---|---|---|

0 |
.002377 |
661.7 |

1,000 |
.002308 |
659.5 |

2,000 |
.002241 |
657.2 |

3,000 |
.002175 |
654.9 |

4,000 |
.002111 |
652.6 |

5,000 |
.002048 |
650.3 |

6,000 |
.001987 |
647.9 |

7,000 |
.001927 |
645.6 |

8,000 |
.001868 |
643.3 |

9,000 |
.001811 |
640.9 |

10,000 |
.001755 |
638.6 |

15,000 |
.001496 |
626.7 |

20,000 |
.001266 |
614.6 |

25,000 |
.001065 |
602.2 |

30,000 |
.000889 |
589.5 |

35,000 |
.000737 |
576.6 |

36,089 * |
.000706 |
573.8 |

40,000 |
.000585 |
573.8 |

45,000 |
.000460 |
573.8 |

50,000 |
.000362 |
573.8 |

55,000 |
.000285 |
573.8 |

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Mach Number

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WWW pages edited by Jonathan G. Fairman - August 1996

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