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I. Force
A. Forces can cause a resting
object to move, or accelerate
a moving object by changing
its speed or direction.
B. A force is a push or pull
acting on an object.
I. Force
C. Force is measured in Newton’s
and are represented by an arrow
that points in the direction of the
force.
II. Combining Forces
A. Net force is the overall force
acting on an object after all
force are combined.
B. Forces acting in the same
direction are added
together.
II. Combining Forces
C. Forces acting in opposite
directions are subtracted.
D. Balanced forces mean
that there is no net force,
no acceleration. (forces
cancel out)
II. Combining Forces
Balanced forces means there is
no change in motion.
An object may move with a
constant velocity if forces are
balanced.
II. Combining Forces
E. Unbalanced forces means
that a net force is present.
Forces do not cancel out,
and motion changes.
ex. Losing tug of war
II. Combining Forces
F. When unbalanced forces are
present the object will
accelerate in the direction of
the larger force.
III. Friction
A. Friction is a force that opposes motion
B. The 4 main types of friction are:




Static – keeps objects at rest
Sliding – acts when sliding across a
surface.
Rolling – much less than sliding
Fluid – friction with gases or liquids
IV. Gravity
A. Gravity is the force between any
two masses. Gravity pulls objects
together.
B. The force of gravity causes objects
to accelerate as they fall.
C. Air resistance slows falling objects
D. Terminal velocity is the fastest
speed a falling object can reach. At
terminal velocity the force of gravity is
balances by the force of friction (air
resistance).
• When object reaches terminal
velocity it continues to move with a
constant velocity.
Weight and Mass
Mass is the amount of matter an object
contains.
An object’s mass does not change - no
matter the location.
The SI unit for mass is kilogram (kg)
Weight and Mass
Weight is the force that gravity exerts on
an object due to its mass.
The weight of an object is directly
proportional to mass and the gravitational
acceleration acting on the object.
W=mg
Weight and Mass
Your weight will change based on
gravity.
Earth’s gravitational acceleration is 9.8
m/s2.
The SI unit for weight is the Newton (N).