THORNHILL SECONDARY SCHOOL PHYSICS WEB PAGE

NEWTON'S LAWS OF MOTION

    It is necessary to describe motion in order to understand Newton's Laws of Motion.  Motion is defined as a movement or a change of position or place. It is possible to calculate and measure these changes by using displacement, velocity, and acceleration formulas.  Kinematics is the branch of physics dealing with different kinds of motion that are possible for a body or system of bodies, without reference to mass or to the force producing the motion. Dynamics is the branch of physics that deals with the study of the motion of bodies and the relation between motion and the forces producing it.  Mechanics, the study of motion, is a branch of physics which is the combination of dynamics and kinematics.
   

    Newton's Laws of Motion describe force's effect on the motion of an object. Sir Isaac Newton (1642-1727), a British scientist, described his three laws in his famous book Principia Mathematica which is published in 1687.

These three(3) laws are:

1) Newton's First Law of Motion (Law of Inertia)

2) Newton's Second Law of Motion (Law of Motion)

3) Newton's Third Law of Motion (Law of Action&Reaction)

To understand Newton's Laws of Motion better, we should know the definitions of specific terms. Click here if you want to learn them.



NEWTON'S FIRST LAW OF MOTION(Law of Inertia): Newton's First Law of Motion suggests that "When no net or resultant force acts upon it, a body at rest remains at rest and a body in motion continues to move in the same direction in a straight line with constant speed." (click here if you want to see a demonstration)

F_NET= 0  then   V = constant 

V = constant  then  FNET= 0

NEWTON'S SECOND LAW OF MOTION(Law of Motion): Newton's Second Law of Motion suggests that "When an unbalanced force acts upon a body, it accelerates that body in the direction of the force.  The acceleration produced is directly proportional to the force."

UNITS                   

NEWTON'S THIRD LAW OF MOTION(Law of Action&Reaction): Newton's Third Law of Motion suggests that "Every action or force is accompanied by an equal and opposite reaction or force." (click here if you want to see a demonstration)

Fa(action force) = -Fb(reaction force)

By clicking here you can see illustrations of this law.

Things to consider when solving problems about Newton's Laws:

1) Read the question carefully and write down what's given

2) Draw the free body diagram(s) which show(s) all the forces acting on the object(s)

3) Try to figure out which law applies to the question

4) Use the formula needed

Then, you should be able to solve the question

LINKS TO OTHER HELPFUL WEB PAGES

1) Newton's Laws of Motion

2)  Chapter Three:  The Laws of Motion

3) Newton's Laws of Motion (Glenbrook South High Sschool)

4)  Forces & Newton's Laws

5)  Newton's First law

6)  Newton's Laws

I do not know what I may appear to the world; but to myself I seem to have been only like a boy playing on the seashore, and diverting myself now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.                   

ISAAC NEWTON

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Last updated on Sunday, March 22, 1998.