An object that experience a push or pull has a force exerted on it' The object that is experiencing

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An object that experience a push or pull has a
force exerted on it. The object that is
experiencing the force is called the system. The
world around the object that exerts forces is
called the environment. The symbol F si used to
represent a force vector.
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Net Force
The sum of all forces acting on an object.
The unit for force is Newton (N).
1 N 1 kg m
s
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Newton's
Laws
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Newton's Second Law
The acceleration of an object is directly
proportional to the net force applied.
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Two horizontal forces, 225 N and 165 N, are
exerted on a canoe. If these forces are applied
in the same direction, find the net horizontal
force on the canoe.
If the same two forces are exerted on the canoe
in the opposite directions, what is the net
horizontal force on the canoe?
Three confused sled dogs are trying to pull a
sled across the Alaskan snow. Alutia pulls east
with a force of 35 N, Seward also pulls east but
with a fore of 42 N, and Kodiak pulls west with a
force of 53 N. What is the net force on the sled?
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Newton's first Law
An object that is at rest will remain at rest or
an object that is moving will continue to move in
a straight line with constant speed, if and only
if the net force acting on that object is zero.
Equilibrium - the net force on an object is zero
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Newton's first law is often called the law of
inertia. Inertia is the tendency of an object to
resist change.
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Free body diagrams
Draw a free-body diagram of a bag of sugar being
lifted by your hand at a constant speed.
Draw a free-body diagram of a water bucket being
lifted by a rope at an increasing speed.
Draw a free-body diagram of a water bucket being
lifted by a rope at a decreasing speed.
Copy table 6-2 Pg 124 7-11
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Weight Force Fg
Consider a ball falling, what are the forces
acting on it?
Acceleration due to gravity is g 9.8 m/s2.
Newton's second law then becomes
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Anna is holding a stuffed dog, with a mass of
0.30 kg, when Sarah decides that she wants it and
tries to pull it away from Anna. If Sarah pull
horizontally on the dog with a force of 10.0 N
and Anna pulls with a horizontal force of 11.0 N,
what is the horizontal acceleration of the dog?
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Your mass is 75 kg. You stand on a bathroom
scale in an elevator. Going up! Starting from
rest, the elevator accelerates at 2.0 m/s2 for
2.0 s, then continues at a constant speed. What
is the force on the scale during the acceleration?
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A 50 kg bucket is being lifted by a rope. The
rope is guaranteed not to break if the tension is
500 N or less. The bucket started at rest, and
after being lifted 3.0 m, it is moving at 3.0
m/s. Assuming that the acceleration is constant,
is the rope in danger of breaking?
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Normal Force FN
a force perpendicular to the surface that is
pushing one surface against the other.
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Friction Force Ff
There are two types of frictional forces
Static Friction

• opposes the start of relative motion between the
  two surfaces in contact

• stops movement from starting

Kinetice Friction

• opposes motion between surfaces in contact

• stops movement that has started

Ff kFN
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You push a 25 kg wooden box across a wooden floor
at a constant speed of 1.0 m/s. If the
coefficient of friction is 0.2, how much force do
you exert on the box?
What if the force you exert on the box is
doubled, what is the resulting acceleration of
the box?
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Review
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