Intro to Motion
Speed vs. Velocity
Speed & Velocity on a Graph
Average Speed vs. Instantaneous
Speed
Objectives
 11.2.1) Explain the difference
between speed and velocity
 11.2.2) Identify the appropriate SI
units for measuring speed and
velocity
 11.2.3) Use a distance time graph to
determine the relative speed of a
moving object
Objectives
 11.2.4) Explain the similarities and
differences between average speed
and instantaneous speed
 11.2.5) Describe how two velocities
combine to produce a resultant
velocity
Speed
 Ratio of the distance
an object moves and
the time it takes to
move that distance
 SI Unit: meters per
second (m/s)
d
s
t
Speed
d 50m
s 
t
6s
Calculate the speed of the
runner
d 400m
s 
t 70sec
Average Velocity
 A ratio between the displacement of
an object and the time it takes to
complete that displacement
 SI Unit: (m/s)
vavg
x

t
Velocity
 A description of both the speed and
direction that an object is moving
Calculate the average
velocity
Velocity
 A description of both the speed and
direction that an object is moving
 Velocity is a vector – it has
magnitude (how fast is it moving?)
and direction (which way is it
moving?)
Calculate the average
velocity
Speed vs. Velocity
d 400m
s 
t 70sec
Speed vs. Velocity
vavg
x 0m


t
70s
Average vs. Instantaneous
Speed
 Average Speed: the total distance
traveled (d) divided by the total time
it takes to travel that distance (t)
 Instantaneous Speed: rate at which
an object is moving at one particular
moment in time
Calculating Speed &
Velocity
 A roller coaster travels a distance of
800 m in 25 sec. What is the
average speed of the roller coaster?
 How long would it take to drive to
Cedar Point, which is 70 miles away,
if you drive with an average speed of
65 mi/hr?
Determining Speed from a
Graph
 Which swimmer is faster?
 Swimmer 1 (white cap) travels a farther
distance is the same amount of time
On a graph of distance vs.
time…
Small slope =
low speed
Big Slope = high
speed
Average Speed vs.
Instantaneous Speed
Speed
Combining Velocities
 A fish is swimming in the water at 2
m/s. The current is moving in the
same direction as the fish at 1.5 m/s.
What is the velocity of the fish as
seen by a person sitting on the
dock?
2 m/s
1.5 m/s
Combining Velocities
 A fish is swimming in the water at 2
m/s. The fish is swimming against a
current moving at 1.5 m/s. What is
the velocity of the fish as seen by a
person sitting on the dock?
2 m/s
1.5 m/s