# Section 2.1 Forces change motion by T66DN35

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```									SECTION 2.1
FORCES CHANGE MOTION
Mrs. Leos
FORCES
 A push or a pull
 Three types
   Contact Force
   When objects use force by pushing or pulling an object.
 Gravity
 Friction
VECTORS
 A quantity that measures both size and direction
 Force is a vector
 Direction of arrow is direction of force
 Size of arrow is size of force (bigger arrow = more
force, smaller arrow = less force)

   What other kind of vector have you already learned
NET FORCE
 Overall force acting on an object when all the
forces are combined.
 Total force that affects an object when multiple
forces are combined.
   The net force depends on both the direction and the
size of individual forces.
BALANCED FORCES           Unbalanced Forces
 Object does not move     Object moves
 No net force             Net force in one
 Same effect as no         direction
force                    One force on an object
 Also act on object        is greater than another
moving in straight
line with constant
velocity
MEASURING NET FORCE
1.   Identify forces to combine.
2.   Put tail of second force arrow to tip of first.
Maintain size and direction
3.   Measure from tail of first arrow to tip of second
force arrow.
COMBINING FORCES IN OPPOSITE
DIRECTIONS
COMBINING FORCES IN THE SAME
DIRECTION
NEWTON’S FIRST LAW
 Objects    at rest remain at rest, and
objects in motion remain in motion
with the same velocity, unless acted
upon by an unbalanced force
 Objects with no net force acting on them have
either constant velocity or zero velocity
 Force is needed to start, change, or stop motion
INERTIA
 Resistance of an object to a change in motion
 Directly related to an object’s mass

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