The discovery of Newton’s laws of motion was a dramatic moment in the history of science. In narrow sense, it was simply a specific paradigm shift in modern science. This shift was initiated by Copernicus, established by Galileo and Kepler, and completed by Newton. These laws of dynamics unfolded the mystery of motions of planets, motions of pendulum, springs and every observable motion.
Galileo discovered the principle of inertia: if an object is left alone, is not disturbed, it continues to move with a constant velocity in a straight line if it was originally moving, or it continues to stand still if it was just standing still.
How an object changes its velocity if something is affecting it, this rule was found by Newton by formulating three laws of motions.
First Law of Motion
The first law of motion is a mere restatement of the Galilean principle of inertia.
Second Law of Motion
The second law specifies a way of determining how the velocity changes under the influence of forces. It asserts that the motion of object is changed by forces in this way: the time rate of change of a quantity called momentum is proportional to the force.
Momentum is different from the velocity. It is a product of mass and velocity. Mass is a quantitative measure of inertia. The mass of an object is constant, the same all the time, otherwise the equations become meaningless.
The second law of motion defines the concept of a force. Newton himself gave an example of gravity. Near the earth’s surface, the force in the vertical direction due to gravity is proportional to the mass of the object and is nearly independent of the heights.
Before the discovery of laws of motion, even the calculation of the motion of a mass on a spring was unknown. But with Newton’s laws, even the complex motion of the planets can be calculated to the higher degree of precision.
Third Law of Motion
It states; action equals reaction. Suppose we have two particles and suppose that the first one exerts a force on second one, pushing it with a certain force. Then simultaneously, according to Newton’s third law, the second particle will push on the first with an equal force, in opposite direction. Furthermore, these forces effectively act in the same line.
These laws of dynamics have interesting consequences. The law of conservation of momentum is derived from Newton’s laws of motion. In addition to the law of conservation of momentum, there is another interesting consequence, that the laws of physics are same whether we are standing or moving with a uniform speed in a straight line.
