Classical mechanics is based onIsaac Newton'sthree laws of motion, which constituted the basis of the whole of classical physics. In 1687, Newton first published the three laws in hisPrincipia, whose full title isThe Mathematical Principles of Natural Philosophy.Until the beginning of the 20th century, classical physics was considered correct, and, in fact, serves even to this day to explain familiar everyday activities.

## The laws of motion - Newton's dynamics:

## The first law - the law of momentum.

This law posits that every body remains at rest or moves with constat velocity in a straight line, unless it is compelled to change that state by a force acting upon it.

This law posits that every body remains at rest or moves with constat velocity in a straight line, unless it is compelled to change that state by a force acting upon it.

This law does not require that no force be exerted on the body, but only that the sum of the forces exerted should be zero.

For example: An ice skater moving at a speed of 5 meters per second will continue to move at this speed so long as nothing stops him (when he reaches the wall at the end of the rink he is sure to come to a stop). In this example the skater is subjected to two forces which cancel each other out: The force of gravity (exerted on the skater's mass) and the "normal force" exerted on the skater by the skating surface. These forces cancel each other so their sum is zero.

## The second law - the law of acceleration.

This law posits that the acceleration of an object is directly proportional to the force causing it. The relationship between the acceleration and the force is determined by the mass (the amount of material) of the object. The greater the sum of forces acting on the body, the greater its acceleration.

Galileo's law of fallis a specific example of Newton's second law of motion which deals with constant forces. In this case (of a constant force), the distance which the object traverses is directly proportional to the square of time.

## The third law - the law of action and reaction.

The action of a force exerted by one body on a second body produces a reaction that is equal and opposite in direction to the action.

This law means that if I exert my weight on the floor, the floor exerts an equal force on me. A more surprising result of this law is that if I exert force on a carriage which begins to move, it exerts an opposing force on me.

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