## Laws of Motion – Class 11 | Chapter – 5 | Physics Short Notes Series PDF for NEET & JEE

Laws of Motion: The laws of motion are a set of three fundamental principles developed by Sir Isaac Newton to describe the behavior of objects in motion. These laws provide the foundation for classical mechanics and help explain how objects move, how forces affect motion, and how systems interact with each other.

## Laws of Motion

The laws of motion are a set of three fundamental principles that describe the behavior of objects in motion. They were first described by Sir Isaac Newton in his book “Philosophiæ Naturalis Principia Mathematica” (Mathematical Principles of Natural Philosophy) in 1687. The laws of motion are:

• Law of Inertia: An object at rest tends to stay at rest, and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force. This is also known as Newton’s first law of motion.
• Law of Acceleration: The acceleration of an object is directly proportional to the force applied to it, and inversely proportional to its mass. This is also known as Newton’s second law of motion.
• Law of Action-Reaction: For every action, there is an equal and opposite reaction. This means that whenever one object exerts a force on another object, the second object exerts an equal and opposite force back on the first object. This is also known as Newton’s third law of motion.

Together, these laws provide a framework for understanding the motion of objects and the forces that affect them. They are fundamental to many areas of science and engineering, including mechanics, thermodynamics, and astrophysics.

## Types of Laws of Motion

Newton’s Laws of Motion laid the foundation for classical mechanics today. Although subject to minor limitations, these laws of motion are valid everywhere and are therefore used. The laws are given as stated below in a brief description

• First Law: Any object will remain in its existing state of motion or rest unless a net external force acts on it.
• Second Law: If an object has a certain mass, the greater the mass of this object, the greater will the force required to be to accelerate the object. It is represented by the equation F = ma, where ‘F’ is the force on the object, ‘m’ is the mass of the object and ‘a’ is the acceleration of the object.
• Third Law: For every action, there is an equal and opposite reaction.

## Types of Motion in Physics

The motion of an object depends on the type of force acting on the body. Examples of different kinds of motion are given below.

• Translational – It is the type, where an object moves along a path in any of the three dimensions.
• Rotational – It is the type, where an object moves along a circular path about a fixed axis.
• Linear – It is a type of translational motion where the body moves in a single direction along a single dimension.
• Periodic – It is the type of motion that repeats itself after certain intervals of time
• Simple Harmonic  It is the type of motion like that of a simple pendulum where a restoring force acts in the direction opposite to the direction of motion of the object. This restoring force is proportional to the displacement of the object from the mean position.
• Projectile  It is the type of motion which has a horizontal displacement as well as vertical displacement.
• Oscillatory  It is the type of motion which is repetitive in nature within a time frame. If it is mechanical it is called vibration.

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