Detailed Notes on Newton’s First Law of Motion for JEE Preparation

1. Inertia

• Definition of inertia: Inertia refers to the tendency of an object to resist any change in its state of motion, whether it is at rest or in motion.
• Units of inertia: The SI unit of inertia is kilogram (kg). It quantifies the mass of an object and its resistance to changes in motion.
• Factors affecting inertia: The inertia of an object depends primarily on its mass. The greater the mass of an object, the greater its inertia.
• Applications of inertia: Inertia plays a crucial role in various situations, such as:
• Difficulty in starting a stationary object or stopping a moving object.
• Resistance to changes in the direction of motion.
• Tendency of objects to maintain their state of motion during sudden stops or acceleration.
• Moment of inertia: Moment of inertia is a quantity that measures an object’s resistance to angular acceleration. It depends on the object’s mass and its distribution relative to the axis of rotation.

2. Law of Inertia

• Statement of Newton’s first law of motion: Newton’s first law states that an object at rest will remain at rest, and an object in motion will continue moving at a constant velocity in a straight line unless acted upon by an unbalanced external force.
• Distinction between balanced and unbalanced forces: Balanced forces occur when the net force acting on an object is zero, resulting in no change in its motion. Unbalanced forces, on the other hand, result in a non-zero net force that causes a change in the object’s motion.
• Understanding a body at rest and a body in motion: A body is considered at rest if its position does not change relative to a fixed reference point. A body is in motion if its position changes relative to a fixed reference point.
• Examples of Newton’s first law of motion: Examples include:
• A book resting on a table remains at rest until an external force, like a push or a pull, is applied.
• A moving car continues to move at a constant velocity in a straight line unless an unbalanced force, such as braking or turning, is applied.

3. Applications

• Application to objects on earth and in space: Newton’s first law explains why objects on Earth remain at rest or in motion until an external force acts on them. It also applies to objects in space, where they continue moving in a straight line at a constant velocity unless influenced by external forces like gravity.
• Importance of seat belts and airbags: Seat belts restrain passengers during sudden stops or collisions, preventing them from being thrown forward due to inertia. Airbags provide cushioning and reduce the impact on passengers during collisions.
• Structural design and testing: Newton’s first law is crucial in designing and testing structures subjected to dynamic forces, such as earthquakes, winds, and vibrations. Structures are designed to withstand these forces and minimize damage.
• Daily life situations: Inertia explains why passengers tend to fall forward when a bus or car stops suddenly. It also explains the behavior of objects like pendulums and the trajectory of projectiles.
• Significance in engineering fields: Newton’s first law has wide-ranging applications in aviation, space technology, and other engineering fields, where understanding and managing inertial effects is essential for designing safe and efficient systems.

4. Related Concepts

• Relationship between Newton’s first law and momentum: Newton’s first law is directly linked to the concept of momentum. Momentum is the product of an object’s mass and velocity. According to the first law, an object’s momentum remains constant in the absence of unbalanced external forces.
• Connection with Galileo’s experiments: Galileo Galilei conducted experiments that challenged Aristotelian notions of motion and supported the concept of inertia. His observations and experiments laid the groundwork for Newton’s laws of motion.
• Understanding pseudo forces: Pseudo forces are fictitious forces that appear to act on objects in non-inertial reference frames. Centrifugal force is an example of a pseudo force that arises when an object is rotating. It is related to inertia and the object’s tendency to resist changes in its state of motion.

5. Problem-solving To strengthen problem-solving skills related to Newton’s first law of motion, candidates should practice solving numerical problems and conceptual questions from:

• NCERT Physics Class 11, Chapter 5: Laws of Motion
• NCERT Physics Class 12, Chapter 5: Laws of Motion
• Previous years’ JEE Main and Advanced question papers

By understanding these subtopics and solving problems, candidates can deepen their comprehension of Newton’s First Law of Motion and prepare effectively for the JEE exam.