Resource Lesson
Newton's Laws of Motion
Printer Friendly Version
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}
Related Documents
Lab:
Labs -
Coefficient of Friction
Labs -
Coefficient of Friction
Labs -
Coefficient of Kinetic Friction (pulley, incline, block)
Labs -
Conservation of Momentum in Two-Dimensions
Labs -
Falling Coffee Filters
Labs -
Force Table - Force Vectors in Equilibrium
Labs -
Inelastic Collision - Velocity of a Softball
Labs -
Inertial Mass
Labs -
LabPro: Newton's 2nd Law
Labs -
Loop-the-Loop
Labs -
Mass of a Rolling Cart
Labs -
Moment of Inertia of a Bicycle Wheel
Labs -
Relationship Between Tension in a String and Wave Speed
Labs -
Relationship Between Tension in a String and Wave Speed Along the String
Labs -
Static Equilibrium Lab
Labs -
Static Springs: Hooke's Law
Labs -
Static Springs: Hooke's Law
Labs -
Static Springs: LabPro Data for Hooke's Law
Labs -
Terminal Velocity
Labs -
Video LAB: A Gravitron
Labs -
Video LAB: Ball Re-Bounding From a Wall
Labs -
Video Lab: Falling Coffee Filters
Resource Lesson:
RL -
Advanced Gravitational Forces
RL -
Air Resistance
RL -
Air Resistance: Terminal Velocity
RL -
Forces Acting at an Angle
RL -
Freebody Diagrams
RL -
Gravitational Energy Wells
RL -
Inclined Planes
RL -
Inertial vs Gravitational Mass
RL -
Non-constant Resistance Forces
RL -
Properties of Friction
RL -
Springs and Blocks
RL -
Springs: Hooke's Law
RL -
Static Equilibrium
RL -
Systems of Bodies
RL -
Tension Cases: Four Special Situations
RL -
The Law of Universal Gravitation
RL -
Universal Gravitation and Satellites
RL -
Universal Gravitation and Weight
RL -
What is Mass?
RL -
Work and Energy
Worksheet:
APP -
Big Fist
APP -
Family Reunion
APP -
The Antelope
APP -
The Box Seat
APP -
The Jogger
CP -
Action-Reaction #1
CP -
Action-Reaction #2
CP -
Equilibrium on an Inclined Plane
CP -
Falling and Air Resistance
CP -
Force and Acceleration
CP -
Force and Weight
CP -
Force Vectors and the Parallelogram Rule
CP -
Freebody Diagrams
CP -
Gravitational Interactions
CP -
Incline Places: Force Vector Resultants
CP -
Incline Planes - Force Vector Components
CP -
Inertia
CP -
Mobiles: Rotational Equilibrium
CP -
Net Force
CP -
Newton's Law of Motion: Friction
CP -
Static Equilibrium
CP -
Tensions and Equilibrium
NT -
Acceleration
NT -
Air Resistance #1
NT -
An Apple on a Table
NT -
Apex #1
NT -
Apex #2
NT -
Falling Rock
NT -
Falling Spheres
NT -
Friction
NT -
Frictionless Pulley
NT -
Gravitation #1
NT -
Head-on Collisions #1
NT -
Head-on Collisions #2
NT -
Ice Boat
NT -
Rotating Disk
NT -
Sailboats #1
NT -
Sailboats #2
NT -
Scale Reading
NT -
Settling
NT -
Skidding Distances
NT -
Spiral Tube
NT -
Tensile Strength
NT -
Terminal Velocity
NT -
Tug of War #1
NT -
Tug of War #2
NT -
Two-block Systems
WS -
Advanced Properties of Freely Falling Bodies #1
WS -
Advanced Properties of Freely Falling Bodies #2
WS -
Calculating Force Components
WS -
Charged Projectiles in Uniform Electric Fields
WS -
Combining Kinematics and Dynamics
WS -
Distinguishing 2nd and 3rd Law Forces
WS -
Force vs Displacement Graphs
WS -
Freebody Diagrams #1
WS -
Freebody Diagrams #2
WS -
Freebody Diagrams #3
WS -
Freebody Diagrams #4
WS -
Introduction to Springs
WS -
Kinematics Along With Work/Energy
WS -
Lab Discussion: Gravitational Field Strength and the Acceleration Due to Gravity
WS -
Lab Discussion: Inertial and Gravitational Mass
WS -
net F = ma
WS -
Practice: Vertical Circular Motion
WS -
Ropes and Pulleys in Static Equilibrium
WS -
Standard Model: Particles and Forces
WS -
Static Springs: The Basics
WS -
Vocabulary for Newton's Laws
WS -
Work and Energy Practice: Forces at Angles
TB -
Systems of Bodies (including pulleys)
TB -
Work, Power, Kinetic Energy
PhysicsLAB
Copyright © 1997-2019
Catharine H. Colwell
All rights reserved.
Application Programmer
Mark Acton