Chapter 2

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Chapter 2Motion and Force

• Section 1Describing Motion

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Motion and Speed

• Motionoccurs when an object changes its position
• Motion doesnt always have to be seen to have
  taken place
• Reference Point-used to determine how far
  something moves
• Ex mailbox while driving

3
Relative Motion

• Relative Motion
• Not all motion is obvious
• Everything is in motion relative to something
  else
• Ex the Earth is always in motion around the
  sun, etc.

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Distance and Displacement

• Distancedescribes how far something has moved
• SI base unit to measure distance is METER
• Displacementthe distance and direction of an
  objects change in position from the starting
  point
• See figure 2 on pg. 39

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Speed

• Speed-the distance an object travels per unit of
  time
• Ex miles per hour/ feet per minute, etc.
• Rateany change over time, so--
• Speed is a RATE
• Equation Speed Distance / Time
• (typically measured in m/s)

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Practice Calculating Speed-pg. 42- 1 and 2

• Most speeds arent constant, they either slow
  down or speed up
• Average speed-describes speed of motion when
  speed is changing
• (driving on a 3 hr. trip)
• Instantaneous Speed-speed at a given point in
  time
• Ex speed on a speedometer

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Velocity

• Velocity--includes the speed of an object AND the
  direction of its motion
• Velocity can change EVEN IF speed remains
  constant
• Change in Velocitycan be EITHER a change in
  speed OR in direction of movement

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Remember To Calculate Velocity, it is the same
as calculating speed, but you must also report a
DIRECTION-north, south, east, west, etc. One
example of change in velocitywhen a race car at
a constant speed is rounding a curve, velocity is
changing, due to direction of travel changing
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Plate Tectonics

• The motion of the Earths crust creates the
  continental drifting that occurs every year
• Plate Tectonics Theory-Pangea
• Plates move so slowly that their speeds are given
  in units of centimeters per year.
• Australian plate-1 of fastestmoves north at an
  average speed of 17 cm./yr and San Andreas Fault
  (in CA) about 1 cm/yr

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Section 2Acceleration Acceleration-the rate of
change of velocity (velocity speed
w/direction) When the velocity of an object
changes, the object is accelerating So
Acceleration occurs when an object changes its
SPEED, its DIRECTION or BOTH
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Acceleration If speed is increasing positive
acceleration (acceleration) If speed is
decreasing negative acceleration
(deceleration) Ex horse on a
carousel-acceleration due to direction only
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Equation for finding Acceleration Acceleration
change in velocity / time OR Acceleration
final velocity initial velocity /
time (usually reported in m/s/s or m/s2) (if
motion is in a straight line, (no change in
direction, use change in speed to calculate
acceleration)
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Amusement Park Acceleration Wooden and steel
roller coaster provide different thrills due to
different materials Wooden-swaying
effect Steel-more loops, steep inclines, drops,
etc.
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Section 3 Motion and Forces Force a push or
pull that one body exerts on another A force
can cause the motion of an object to change ex
tennis racket on a ball ex billiards
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Balanced forces forces that are equal, but in
opposite directions they do NOT change the
direction of the force NET FORCE-when two
balanced forces are combined the net force will
be zero (if equal but in opposite directions)
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Unbalanced forces forces that are unequal and
in opposite directions the greater force will
cause an object to move in that direction NET
FORCE with unbalanced forces, will be the
DIFFERENCE BETWEEN the two forces
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Inertia The tendency of an object to resist ay
change in its motion If an object is moving, it
will keep moving at the same speed and direction
unless an unbalanced force acts on it Or
velocity of the object remains constant unless a
force changes it
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Newtons First Law of Motion (Also called Law of
Inertia) An object in motion will remain in
motion unless acted upon by an outside force An
object at rest will remain at rest unless acted
upon by an outside force Ex what happens in a
car crash-pg. 55