Chapter 1, Section 1
Describing and Measuring Motion
Describing Motion
O Not always easy to describe if an
object is moving
O “An object is in motion if its
distance from another object is
changing.” (p7)
O Reference Point – a place or object
used for comparison to determine if
something is in motion. (p7)
O Use objects like trees or buildings
O The answer to the question “is it
moving?” depends upon the reference
point chosen.
O Ex. A chair vs. the sun (p.8)
O Use measurement to be more specific
when describing motion.
O International System of Units (SI) –
system of measurement used by
O Unit of measurement used for length
is meters (m)
O May also be in centimeters (cm),
millimeters (mm), etc.
Calculating Speed
O You can calculate speed if you know both
the distance and object traveled and how
long it took to reach its destination.
O Speed = Distance / Time
O If distance is measured in meters and time
is measured in seconds, your answer would
be labeled m/s (meters per second).
O Most objects to not move at a
continuous speed. It changes as the
object moves (may speed up or slow
O Average Speed – total distance
traveled divided by the total time.
O Instantaneous Speed – the rate at
which an object is moving at a specific
Describing Velocity
O To fully describe the motion of an object you
also need to know the direction it is
O Velocity – speed in a given direction
O Ex. 25 mph west
O Important for air traffic controllers to know
the speed and direction of planes
O Important for pilots and stunt pilots to be
able to keep control of the airplane
Graphing Motion
O To show motion in a graph, create a
line graph.
O Time is on the x-axis
O Distance is on the y-axis