Mechanics

Newtons 1^st law

According to Newton's first law, an object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force. It is the natural tendency of objects to keep on doing what they're doing. All objects resist changes in their state of motion. In the absence of an unbalanced force, an object in motion will maintain this state of motion. This is often called the law of inertia.

Since these two forces are of equal magnitude and in opposite directions, they balance each other. The book is said to be at equilibrium. There is no unbalanced force acting upon the book and thus the book maintains its state of motion.

The presence of an unbalanced force will accelerate an object – changing its speed, its direction, or both its speed and direction.

Newton's 2^nd Law

The Physics Classroom: Lesson 3: Newton's Second Law of Motion

The Physics Classroom: Newton's Laws: Elephant and Feather - Free Fall

The Physics Classroom: Newton's Laws - Skydiving

Terminal velocity

Newton's 3^rd Law

Lesson 4: Newton's Third Law of Motion

"For every action, there is an equal and opposite reaction."

The statement means that in every interaction, there is a pair of forces acting on the two interacting objects. The size of the force on the first object equals the size of the force on the second object. The direction of the force on the first object is opposite to the direction of the force on the second object. Forces always come in pairs – equal and opposite action-reaction force pairs.

Circular, Rotational Motion

Feelings of weightlessness and heaviness are associated with the normal force; they have little to do with the force of gravity. A person who feels weightless has not lost weight; the force of gravity acting upon the person is the same magnitude as it always is. Witness in the animation above that the force of gravity is everywhere the same. The normal force however has a small magnitude at the top of the loop (where the rider often feels weightless) and a large magnitude at the bottom of the loop (where the rider often feels heavy).

Newton’s cradle

Java Applets on Physics: Newton's Cradle

Simple harmonic motion and circular motion

Northeastern University, Boston: Simple Harmonic Motion

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