Physics
Chapter 3
Describing Motion
Describing Motion
3.1 Picturing Motion
 Motion diagram
 Operational definition
 Particle model
3.2 Where and When
 Coordinate systems
 Scalar/Vector quantities
 Displacement
 Time interval
3.3 Velocity and Acceleration
 Velocity (average/instantaneous)
 Speed
 Average acceleration
 Problem Solving Strategies
3.1 Picturing Motion
When studying moving
objects it is useful to
understand their
motion by picturing
how that motion
would look.
FAST
OR
SLOW
Motion Diagram
Motion Diagram
A series of images of a moving object that
records its position after equal time
intervals.
Operational Definition of Motion
Before we describe
motion mathematically
we will study motion
in terms of a
procedure or operation
used to identify it.
This is called an
operational
definition.
Motion Diagram
For the next four slides the time between
images is 1 second.
How would you describe the following
motion?
Motion Diagram
For the next three slides the time between
images is 1 second.
How would you describe the following
motion?
Motion Diagram
For the next two slides the time between
images is 1 second.
How would you describe the following
motion?
Motion Diagram
For this slide the time between images is 1
second.
How would you describe the following
motion?
Motion Diagram
Particle Model—instead of using objects we
can replace them with a single point.
This helps to eliminate extraneous motion
3.2 Where and When?
When studying motion
it is important to be
able to locate the
object that you are
studying.
You also may need to
be able to decide if it
is moving.
Frame of Reference
To make position
measurements of an
object you must
choose a reference
frame and a reference
point that is defined to
be stationary and at
point zero.
The wain
Coordinate System
Once a reference frame
has been determined
objects can be located
within it by establishing a
Y-axis
coordinate system
Coordinate system—tells
you the zero point (origin)
and direction of change in
the variable you are
studying.
Motion in 2 directions
Origin
X-axis
Vector
Vector
An arrow that represents
the magnitude and
direction of a quantity
Position vector
Shows the position of an
object relative to the
origin
Direction and distance

Example: 2.5m east
2.5m east
Scalar/Vector Quantities
Scalar Quantities
Tell only the
magnitude of the
measurement
Examples:





Time
Temperature
Mass
Distance
Speed
Vector Quantities
Tell both magnitude
and direction of the
measurement
Examples:



Displacement
Velocity
Acceleration
Distance/Displacement
Distance
Scalar quantity
The length of the path
an object takes.
Displacement
Vector quantity
The change it position
between an object’s
starting position and
the ending position
Distance + direction
Distance/Displacement
So what’s the difference
between distance and
displacement?
5m
Total distance traveled
Total displacement
4m
Displacement
d = d1 – do
d (displacement)= d1(ending position) – do(starting position)
Time
Since time is the
separation between the
occurrence of two
events, it is better in
physics to talk about
the time interval in
which something
occurs.
Time
Time interval (t)
The difference between starting time (t0)
and ending time (t1) for an occurrence.
t = t1 – to
3.3 Velocity and Acceleration
In your own words define the physics
term velocity. How is it different from
speed?
3.3 Velocity and Acceleration
What is average velocity and what is its
symbol?
3.3 Velocity and Acceleration
Write the equation for calculating average
velocity. Define all terms.
3.3 Velocity and Acceleration
Explain the difference between average velocity
and average speed.
3.3 Velocity and Acceleration
Explain the difference between average velocity
and instantaneous velocity.
TIME
3.3 Velocity and Acceleration
Explain why we cannot use the equation,
v = (d1 do)/t to solve for instantaneous
velocity.
3.3 Velocity and Acceleration
Show how the equation, v = d/t can be
rearranged to find displacement given average
velocity and time.
3.3 Velocity and Acceleration
Show how the equation, v = (d1 do)/t can be
rearranged to find final position given average
velocity, initial position and time.
3.3 Velocity and Acceleration
Explain how the velocity 15m/s is the same as
15m/s and how it is different.
3.3 Velocity and Acceleration
In your own words, define acceleration.
3.3 Velocity and Acceleration
What is average acceleration and what is its
symbol?
3.3 Velocity and Acceleration
Write the equation for calculating average
acceleration. Define all terms.
3.3 Velocity and Acceleration
Under what set of conditions is acceleration
positive and under what set negative?
In conclusion…………………
Let check our
knowledge!
Measurement
Quantities
Magnitude
+
Direction
Scalar
Vector
displacement
Distance
Speed
Velocity
Acceleration