Physics

Newtons Laws of Motion



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Isaac Newton is considered as the finest brain in science the world has ever produced. His discovery in science (then called natural Philosophy) is called Classical Mechanics (or more accurately Newtonian Mechanics). He gave three fundamental laws in Mechanics , called Newton's Laws of Motion. These laws are the foundation stone of modern day mechanical engineering. A common man is generally aware of inertia. This is a property by virtue of which a body has a tendency to maintain its natural state . Hence, if a mat is pulled abruptly from the feet of a man standing on it, he falls. This is a example of force which is clearly depicted in Newton's first Law.

1. FIRST LAW: According to Newton's first law of motion, if a body is at rest or in uniform motion, then it will always maintain that state unless it is acted upon by an external force. In other words, A body persists in its state of rest or uniform motion unless an external force acts on it.

If a body is at rest , then its velocity (v) and acceleration (a) are equal to zero. If a body is moving with uniform velocity, then again acceleration equals zero. Hence, in both cases , acceleration is zero and thus the force acting on it is zero.

In short, F=0↔a=0

In short, every body has a  natural tendency to maintain its initial state of motion unless an external force is applied on it. Newton's second law gives the definition of force.

2. SECOND LAW:  Newton's second law states that if an external force acts on a body, then the magnitude of force is directly proportional to the product of mass of the body and its acceleration. The direction of force is along the direction of motion (if speed increases) or opposite to the direction of motion(if speed decreases). In other words , Newton's second law is an indication of the rate of change in the velocity of a body when a force acts on it.

Mathematically , this relationship is represented as  F=ma

This formula is considered as the cornerstone of Classical mechanics. Modern day mechanical engineering remarkably depends on this formula. in words we can write it as Force = Mass × Acceleration.

3. THIRD LAW: This law is an indication of the direction of force and its reaction when applied on a body. According to Newton's third law, "to every action there is an equal and opposite reaction". An action and reaction are equal in magnitude, opposite in direction and act on different bodies.

According to some modern day Engineers , Newton's third law is not merely a jumble of ten words, but its meaning is rather vast and exploring. Practically , a majority of Mechanical problems can be solved if one has a crystal clear concept of all the three laws formulated by Newton.

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