Linear
Motion
Relative Motion
• Motion is relative
• An object’s motion is always
described in reference to another
object
Relative Motion
• When an object is said to be
traveling at 60 km/h (or at any
speed), it is implied that it is
moving at 60 km/h relative to the
Earth.
Relative Motion
CLICK HERE TO
WATCH THE VIDEO!
Jamiroquai
“Virtual Insanity”
Travelling Without Moving
1997 Video of the Year
Vectors and Scalars
Vector- a quantity possessing both
magnitude and direction
Scalar- a quantity possessing only
magnitude
Vectors and Scalars
Examples of Vectors:
• Displacement (Δx)
• Velocity (v)
• Acceleration (a)
• Force (F)
• Momentum (p)
Vectors and Scalars
Examples of Scalars:
• Distance (d)
• Mass (m)
• Speed (v)
• Time (t)
Speed
Instantaneous speed: the speed
that something has at any one
instance
Average speed: the speed of an
object over a time interval
Speed
The average speed for a trip might
be 53 miles/hour.
However, during this trip your
instantaneous speed might have
been 0 miles/hour at a stoplight...
...or 70 miles/hour on the open road.
Speed
What are the units of speed?
• miles/hour…………….mph
• kilometer/hour……….km/h
• meters/second……….m/s
• furlongs/fortnight?
Speed
1. What is the average speed of a cheetah
that sprints 100 meters in 4 seconds?
2. How about if it sprints 50 m in 2 s?
Velocity
Velocity = {speed with a direction}
Examples:
70 mph is a speed.
70 mph North is a velocity.
Velocity
What are the units of velocity?
Velocity has the same units as
speed except they also have a
direction
Velocity and speed equations
v 2  v1  0
v 2  v1  at
x2  x1  v1t  at
x2  x1  v1t  0
1
2
2
v v  0 v  v  2a( x2  x1 )
2
2
2
1
2
2
2
1
Velocity vs. speed
The speedometer of a car moving to the
east reads 100km/h. It passes another
car that moves to the west at 100km/h.
• Do both cars have the same speed?
• Do they have the same velocity?
Conceptual Review
• In an unusual move by the New York State
Department of Transportation, all of the "speed
limit" signs were replaced with "velocity limit"
signs.
– What would such a sign look like?
– How could one travel faster than the old speed limit
without violating the new velocity limit?
Conceptual Review
• Which device(s) on a car can
be used to change …
–its speed?
–its velocity but not its speed?
Conceptual Review
• A car driving on a circular test track shows a
constant speedometer reading of 100 kph for
one lap.
– Describe the car's speed during this time.
– Describe its velocity.
– How do the speed and velocity compare?
Conceptual Review
• Is it possible for an object to have …
–constant speed and changing
velocity,
–changing speed and constant
velocity?
Conceptual Review
• Why are the devices in cars
called speedometers and
not velocitometers?
Relative Motion…one more time
CLICK HERE TO WATCH THE VIDEO
OK Go
“Here It Goes Again”
Oh No
2007 Grammy award for "Best Short-Form Music Video”
Acceleration
Acceleration is the rate of change of velocity.
Acceleration
What are the units of acceleration?
• miles/hour/second…………….mi/h/s
• kilometer/hour/second……….km/h/s
• meters/second/second……….m/s/s or m/s2
Acceleration equations
v2  v1  at
x2  x1  v1t  at
1
2
2
v  v  2a( x2  x1 )
2
2
2
1
Acceleration
Acceleration is the positive or
negative depending on the
direction of the acceleration.
Acceleration
An object traveling with a constant positive velocity
Acceleration
An object traveling with a constant negative velocity
Acceleration
An object traveling with a positive velocity, positive acceleration.
Acceleration
An object traveling with a positive velocity, negative acceleration.
Acceleration
An object traveling with a negative velocity, negative acceleration.
Acceleration
An object traveling with a negative velocity, positive acceleration.
Graphs of Motion
On a displacement vs. time graph the slope of
the line is equal to the velocity of the object.
On a velocity vs. time graph the slope of the line
is equal to the acceleration of the object.
On a velocity vs. time graph the area underneath
the curve is equal to the displacement of the object.