1.2 SPEED AND VELOCITY
SCALAR
Average speed, v (SI Unit: m/s)
The total distance travelled divided by the
total time taken.
(Other units used: km/h)
d
vav 
t
VECTOR

Average velocity, v (SI Unit: m/s)
The total displacement (or change in position)
divided by the total time taken.
(Other units used: km/h)

vav 

d
t
Recall that the symbol delta, in physics means ‘change in’ and often involves an initial term and final
term. For example t = t2 – t1. In this section, we see a new variable of t, represent a change in time.
The SI Units for time are seconds (s).
Example Problems for Average Speed
(1) A paper airplane flies 3.7 m in 1.8 s. What
is the airplane’s average speed?
G:
S:
(2) A cheetah can run at a max. speed of 30.0
km/h or 8.33 m/s. How far can the
cheetah run in 3.27 s.
G:
S:
R:
S:
R:
S:
A:
A:
Example Problems for Average Velocity
(3) What is the average velocity of a soccer ball (4) A subway train travels at an average
that is kicked and travels 2.17 m [E] in 1.36
velocity of 22.3 km/h [W]. How long will it
s?
take for the subway train to undergo a
displacement of 241 m [W]
G:
S:
G:
S:
R:
R:
S:
A:
A:
S:
POSITION-TIME GRAPHS
What information does a P-T graph give?
Position Time Graph of Peter Parker Running to
Catch the Bus from his Initial Starting Point
Where does the sprinter start?
Where is the sprinter after 3 s?
What is the slope of the graph?
What does it represent?
THE SLOPE OF A POSITION TIME GRAPH IS EQUAL
TO ITS AVERAGE VELOCITY!!!
Rates of Change describes how quickly a quantity is changing. Calculating the slope is
calculating the rate of change. Is Velocity a rate of change?
Motion with Uniform (Constant) Velocity – motion at a constant speed in a straight line
Motion with Non-uniform Velocity- motion that is not at a constant speed or not in a straight line
POSSIBLE POSITION-TIME GRAPHS
The position has not
changed, therefore the
object is not in motion
The object is at a constant
positive position [E] relative
to the reference position
The position has not
changed, therefore the
object is not in motion
The object is at a constant
negative position [W]
relative to the reference
position
The graph is a straight
line with a positive slope
(constant velocity)
The object is moving with
a constant velocity [E]
The graph is a straight
line with a negative slope
(constant velocity)
The object is moving with
a constant velocity [W]
(from the negative slope)
Consider the Following:
What happens if I increase the steepness of the slope of either one of the last two diagrams?
Try this link:
http://www.physicsclassroom.com/Class/1DKin/U1L3a.cfm
HOMEWORK: Read Pages 14-20 and Complete Questions #1-8 on Page 20