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CHAPTER 2
Distance vs. Displacement
• Distance:
• How far an object has
moved
• I ran 10 meters north
and 30 meters south.
How far did I run?
• Displacement:
• How far the object
moved from the
starting point
• What is my
displacement in the
previous problem?
Motion
• Distance- how far object
moved
• Displacement- distance
and direction the object
moved from starting
location
• Speed = distance / time
(Don’t forget units)
• Ex: 5 m/s
Speed
• You travel 10 meters in 2 seconds. What
was your speed?
• Your speed is 100 km/h and you’ve been
driving for 5 hours. How far have you
driven?
Average vs. Instantaneous
• Average speed = total d / total t
• Instantaneous speed = speed at that given
second
Trickier problem
• Sound travels at 330 m/s. If a lightning
bolt hits the ground 1 km away from you,
how long will it take for the sound to reach
you?
Speed vs. Velocity
• Speed = d / t
• Velocity = speed of
object and direction of
its motion
Acceleration
• Change in object’s velocity (speed and direction
of motion)
• Increasing speed =positive acceleration
• Decreasing speed = negative acceleration
• Acceleration = change velocity / time
• Acceleration = (Vf – Vi) / t
• Don’t forget units!
• Ex: 5 m/s2
• Gravitational acceleration 9.8 m/s2
Acceleration
• A jet airliner starts at rest at the end of the
runway and reaches a speed of 300 m/s in
20 seconds. Calculate the acceleration.
Acceleration again
• A skateboarder is moving at a speed of
20m/s and comes to a stop in 2 seconds.
Calculate the acceleration.
Force
• Push or pull on an
object
• Gravity is a basic
force
• Closer objects are
together, the grav
force between them
increases
Balanced Force
• Net force = 0
• Same force in
opposite directions
cancel each other out
• No movement
Unbalanced Force
• Unequal forces in
opposite directions
• Movement occurs
• Net force = # in one
direction
• Centripetal force =
unbalanced force,
with an object
accelerating towards
the center
Inertia
• Tendency of an object to
resist a change in its
motion
• Newton’s 1st Law of
Motion: an object moving
at a constant velocity or
at rest will remain that
way unless it is acted
upon by a force
• Why should we wear
seatbelts?