A physics lesson in speed and velocity – Part 1

Let me walk you thru a session with my children on (un) teaching them basic concepts of speed and velocity… thru a series of posts.

At the end of the posts I will deconstruct the method behind this approach.

Scene 1: Luke Skywalker gets on his pod. He needs to get to the Sand Dunes on the planet of Tatooine. He travels north for 3 Kms. At the Dulcos pass he takes a left turn to go west. He then travels 5 Kms. At that point he suspects that the sand people may be stalking the area ahead. So he turns north again and travels for 7 Kms. He then reaches the Sand Dunes of Tatooine.

  1. Can you draw the journey? Make sure you draw the pod, sand people and the mountains. Any other aliens and planetary images get extra points 🙂
  2. How much did Luke travel in all?
  3. How much did Luke travel North? West?

Luke traveled a ‘distance‘ of 15 Kms in all. In the direction of North he only traveled 10 Kms. So the ‘displacement‘ is 10 Kms North. Similarly, his ‘displacement‘ west is 5 Kms.

Here is the picture from Star Wars on the two suns setting in the planet of Tatooine.

STAR WARS

A shot of Luke Skywalker and his pod.

mark-hamill-as-luke-skywalker-5

As the text book definition [2] goes:

Distance and displacement are two quantities that may seem to mean the same thing yet have distinctly different definitions and meanings.

  • Distance is a scalar quantity that refers to “how much ground an object has covered” during its motion.
  • Displacement is a vector quantity that refers to “how far out of place an object is“; it is the object’s overall change in position.

Displacement has a value and direction (called vector in physics). Distance just has value (called scalar). As we go along we will see why the distinction is needed.

References:

  1. Introduction to displacement, velocity and time in Khan Academy
  2. 1-D kinematics: Distance and displacement from PhysicsClassroom
  3. Tatooine pics
  4. Luke and his pod
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