Describing Motion
Ch 2 sect 1
Challenge

Can you describe motion without using the
word move?
Motion

Motion occurs when an object changes its
position
 When something goes from one spot to
another then motion has occurred

If you are sitting completely still with no
movement, are you in motion?
Relative Motion
The correct answer is yes and no because of
relative motion
Relative motion depends on what we are
comparing motion to
– Sitting completely still you are not in motion
compared to the room you are in
– Even if you are sitting completely still you
are in motion compared to the sun b/c you
are on the earth and the earth is moving
around the sun
Relative Motion, Physics,
and Earth Science
 Science has shown that the surface of the
earth is broken into a bunch of different
sections
– These sections are called plate tectonics
 Plate tectonics are in constant motion,
therefore you are always in motion relative
to other continents.
 What evidence supports plate tectonics
Describing Motion
• There are two words which we will begin
describing motion with.
1. Distance - Distance refers to how far
something has moved
• Distance must have a unit and a number attached
to it
Describing Motion (continued)
2. Displacement - Displacement
describes how far as well as which
direction the object is from its starting
point
Rate and Speed
 Rate-Change

over time
Ex.-rate of growth may be 2 cm’s per year
 Speed-Distance
traveled in a given
amount of time


Speed is measured in meters/sec
To calculate speed we use the equation
Speed = Distance or S = D
Time
T
Types of Speed
There are two different types of speed
Instantaneous Speed-Speed at any
given point and time

1.

Ex.-Looking at the speedometer in your car,
it tells how fast you are traveling now
Types of Speed (cont)
2. Average Speed-Distance covered over a
set time period.


Takes into account the changes in speed
This is where we use our equation for speed
Speed = Distance
Time
Graphing Motion
There are two basic graphs that can be
used when showing motion

1.
2.
Distance-time graph: A distance-time graph
shows how far an object has traveled as well
as how long it took
Displacement-time graph: A displacement
time graph shows how far an object is away
from its starting point
Graphing Motion (continued)
 When



graphing motion
Time is always on the x axis
Distance or Displacement are always on the Y
axis
You can never have a vertical line
• Why???

It is possible to have a horizontal line
• Why??
Velocity
 Velocity
describes the speed and direction
of an object

If you have escalators that are next to each
other and running the exact same speed, do
they have the same velocity?
• Yes or No and why-

If you have have a car that is traveling at 20
meters per second (constantly) in a circle
does that car have the same velocity?
• Yes or No and why-