Module 1 Lesson 2

Module 1—Motion

Lesson Summary

In this lesson and related lab activities you explored the following questions:

How are speed and velocity calculated?
What is the relationship between velocity and acceleration?

Displacement Versus Distance

Distance travelled is a measure of how far an object has moved. Displacement is a measure of the magnitude of a change in position, and it includes an expression of direction.

Quantity	Symbol	SI Unit
displacement (a vector quantity written as with an arrow on top)		m, direction
magnitude of the displacement		m
distance (a scalar and therefore written as Δd without an arrow)	Δd	m

Note that the magnitude of a displacement, , is, in general, different from the distance travelled (Δd).

Average Velocity Versus Average Speed

Average velocity is defined as the ratio of displacement divided by time elapsed. It has both magnitude and direction. Average speed is defined as the ratio of distance travelled divided by time elapsed. It does not have an expression of direction.

Quantity

Equation

SI Unit

average velocity

(displacement divided by time)

m/s, direction

average speed
(distance divided by time)

m/s

Acceleration is a measure of the change in velocity during a given time interval. Therefore, acceleration is a measure of the rate of change of velocity.

Expressed as an equation, it is .

Quantity	Symbol	SI Unit
acceleration		m/s2
change in velocity		m/s
time interval	Δt	s

Δ means change.

Lesson Glossary

acceleration: a measure of the rate of change of velocity in relation to time

distance: the length of the path taken to move from one place to another

speed: a measure of the distance travelled per unit of time

velocity: a measure of the rate of change of position in relation to time