A CIESE Realtime Data Project

CIESE -Navigational Vectors - Lesson #6

Lesson #5

Lesson #6
Frames of Reference

Lesson #7

Ever wonder why things look like they are moving more slowly or more quickly from a different perspective? It all has to do with your frame of reference...

A) How Fast Are You Going??

  1. Look at the first image below. To you, the observer, standing on the ground it looks like both planes are going 100 km/h. In other words, each plane's velocity with respect to the ground is 100 km/h. What if, instead, you were inside one of the planes looking at the other plane. What would the other plane's velocity appear to be from that perspective?

  2. Look at the second image. The planes are now moving at the same speed but in opposite directions. If you were inside one of the planes, what would the other plane's velocity appear to be from that perspective?

B) So Many Velocities

The measured velocities for objects in motion may be different depending on your frame of reference. For airplane navigation there are 3 different velocities that are important. They are:

Plane's Ground Velocity: Velocity of the plane with respect to the ground.
Plane's Air Velocity: Velocity of the plane with respect to the air.
Wind Velocity: Velocity of the air with respect to the ground.


  1. Pilots frequently use terminology that is similar but not exactly like the terms described in a physics text. See if you can translate the physics terms on the left to the pilot terms on the right. Which terms do you think go together?

    Physics Terms   Pilot Terms
    Plane's Ground Velocity ? Air speed (+ directional heading)
    Plane's Air Velocity ? Wind speed (+ directional heading)
    Wind Velocity ? Ground speed (+ directional heading)
  2. A plane's ground velocity is the vector resultant of the plane's air velocity and the wind velocity. Can you draw a vector diagram depicting this?

  3. Can you think of a way to represent this with an equation?

  4. Go to the Flight Tracker web site shown below. Select "Track Random Flight". Look at the speed given for the flight.

    a) Does the speed of the plane represent ground speed or air speed?
    b) What is the difference between ground speed and air speed?
    c) What are the units for speed?
    d) Why do you think the term speed is used instead of velocity?

C) A Look inside the Cockpit

Inside the cockpit, a pilot has a number of instruments that provide flight information. One of them is the air speed indicator. A pilot must know at what air velocity (air speed and direction) to fly the plane in order to maintain a certain ground speed. Take a look at the airplane instrument panels below to see examples of some of the instruments available to a pilot. What instruments can you identify?

D) Ready to Become a Pilot?

  1. A Navy pilot needs to land his plane on an aircraft carrier. Which way should he approach the carrier, from the rear or from the front? Why?

  2. Imagine the movement of an object from an unusual frame of reference. Describe its movement.

  3. There is conflicting testimony in a case regarding an airplane crash on the ground. An observer on the ground claims that the plane was traveling 100 km/h during landing. The pilot argues that he was only going 65 km/h. What might account for the different claims?

  4. What do you think are the most important navigation instruments available to a pilot? Why? (Optional)

  5. Suppose you are on a world of another dimension (e.g. 1, 2, or 4 dimensions). How would your perspective of objects change? (Optional)