Kinematics
Uniform Motion, Velocity &
Speed
Uniform Motion:

When an object moves uniformly

If both speed & direction remain the
same, velocity is constant & is an example
of uniform motion

Ex. an elevator
Velocity:
Is the displacement of an object in a unit
of time
 Rate of change of position
 Vector quantity


 d
v
t
v = velocity
∆d = displacement
∆t = time
Speed:
Is the distance covered by an object in a
unit of time
 Scalar quantity
 The speed and velocity of an object will
often have the same magnitude but, of
course, velocity will have a direction and
speed will not.
s = speed

d
s
t
∆d = distance
∆t = time
Jamaican sprinter Usain Bolt ran 100m in
9.69 seconds at the Beijing Olympics.
Assuming uniform motion, what was his
speed in m/s? km/h?
d
v
t
100
v
9.69
v 10.32m / s
0.1
v
0.00269
v  37km / h
An air traffic controller notices that an
aircraft has a velocity of 360km/h [SW].
What displacement will the plane
experience in the 25s period before the
controller checks its position again?
d
v
t

d
360 
0.00694

d  2.5km[ SW ]
A car travels from a position of 2km [N] to
a position of 20km [S] in half an hour.
What is the car’s velocity?

 d
v
t
22km[ S ]
v
0.5 h

v  44km / h [ S ]
A student leaves school at 4:00pm & eager to
get home (almost 2km away) and start
writing his physics lab report, starts to jog at
a steady rate of 3m/s.
His lab partner leaves school five minutes
later on her bike, follows the same route at
7.0m/s.
What time is it when she catches up with
her partner?
When she catches up, both have traveled
the same distance. But she has traveled
300s less!
distance
traveled
time
y  ax  b
velocity
y  ax  b
y  3x
y  ax  b
y  7x  b
y  7 x  2100
initial value =
distance
“started” at

d
7
300
d  2100m
BEHIND!!!
y  3x
y  7 x  2100
3x  7 x  2100
x  525s
8 min 45 sec
They meet at
4:08:45