Resource Lesson
Newton's Laws of Motion
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The tendency of objects to resist change in their state of motion is called
inertia
. Inertia is measured quantitatively by the object's mass. Objects will undergo changes in motion only in the presence of a net (unbalanced) force.
Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first. This is because a
force
is defined as the interaction between two objects. In the metric system, forces are measured in a unit called a
newton
. Forces occur only in pairs, one action and the other reaction, both of which constitute the interaction between one thing and the other. Neither force exists without the other. Since action and reaction forces act on different objects, action and reaction forces can never cancel each other.
Whenever you speak of
net force
, you are speaking about ALL of the forces acting on one, unique object. These forces are often summarized in a
freebody diagram
. If the forces cancel each other, then the net force acting on the body is equal to zero. When this happens, the object is said to be in a state of equilibrium:
static equilibrium
occurs when the object is at rest;
dynamic equilibrium
occurs when the object is moving at a constant velocity.
When a
net unbalanced force
is impressed upon an object, the object will accelerate. The acceleration is directly proportional to the unbalanced force and is inversely proportional to the object's mass. Symbolically this is written as
a ~ F/m
. Acceleration is always in the direction of the net unbalanced force. An net unbalanced force of 1 N will result in a 1 kg mass experiencing an acceleration of 1 m/sec
^{2}
.
When objects fall in a vacuum, the net force is simply the object's weight and the object is said to be in a state of
freefall
. We state that the acceleration is
a = -g
where the variable
g
denotes that acceleration is due to gravity, 9.8 m/sec
^{2}
. When objects fall through air, the net force is equal to the weight minus the force of air resistance, and the acceleration has a magnitude less than
g
. If and when the force of air resistance equals the weight of a falling object, acceleration terminates, and the object falls at constant speed called its
terminal velocity
.
Law of Inertia
An object will maintain a constant velocity until an unbalanced, outside force acts upon it.
OR
An object at rest will remain at rest, while an object moving at a constant velocity will continue to move in that fashion until it is acted upon by an unbalanced, outside force.
Law of Acceleration
The acceleration an object experiences is directly proportional to, and in the same direction as, the net force acting upon it and is inversely proportional to the object's mass.
net F = ma
Law of Action-Reaction
If object A exerts a force on object B then object B exerts an equal but opposite force on object A.
F
_{AB}
= - F
_{BA}
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Air Resistance
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Forces Acting at an Angle
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Freebody Diagrams
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Action-Reaction #2
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Equilibrium on an Inclined Plane
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Falling and Air Resistance
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Force and Acceleration
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Force and Weight
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Force Vectors and the Parallelogram Rule
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Freebody Diagrams
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Gravitational Interactions
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Incline Places: Force Vector Resultants
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Incline Planes - Force Vector Components
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Inertia
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Mobiles: Rotational Equilibrium
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Net Force
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Newton's Law of Motion: Friction
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Static Equilibrium
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Tensions and Equilibrium
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Acceleration
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Air Resistance #1
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An Apple on a Table
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Apex #1
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Apex #2
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Falling Rock
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Falling Spheres
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Friction
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Frictionless Pulley
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Gravitation #1
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Head-on Collisions #1
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Head-on Collisions #2
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Ice Boat
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Rotating Disk
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Sailboats #1
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Sailboats #2
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Scale Reading
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Settling
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Skidding Distances
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Spiral Tube
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Tensile Strength
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Terminal Velocity
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Tug of War #1
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Tug of War #2
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Two-block Systems
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Advanced Properties of Freely Falling Bodies #1
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Advanced Properties of Freely Falling Bodies #2
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Charged Projectiles in Uniform Electric Fields
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Combining Kinematics and Dynamics
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Distinguishing 2nd and 3rd Law Forces
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Force vs Displacement Graphs
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Static Springs: The Basics
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Vocabulary for Newton's Laws
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Work and Energy Practice: Forces at Angles
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Systems of Bodies (including pulleys)
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Work, Power, Kinetic Energy
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