Class 11 Physics - CBSE
Laws of Motion
The chapter 'Laws of Motion' in Class 11 Physics builds upon the concept of kinematics by exploring *why* objects move. You will study Newton's three fundamental laws of motion, the principle of conservation of linear momentum, and the concepts of inertia and force. Special emphasis is given to real-world applications like friction, circular motion, and solving problems involving connected bodies on inclined planes using free-body diagrams. This chapter is exceptionally important for CBSE board exams as it forms the bedrock of classical mechanics, carrying around 6 to 8 marks, and frequently appears in numerical and conceptual questions.
Start Learning FreeKey Concepts
Newton's First Law of Motion
An object continues to remain at rest or in uniform motion unless acted upon by an external net force. This property of resisting changes in state is called inertia.
Newton's Second Law of Motion
The rate of change of linear momentum of a body is directly proportional to the applied external force and takes place in the direction in which the force acts (F = ma).
Newton's Third Law of Motion
To every action, there is always an equal and opposite reaction acting on two different bodies simultaneously.
Conservation of Linear Momentum
The total linear momentum of an isolated system of interacting bodies remains conserved if no external net force acts on the system.
Friction (Static and Kinetic)
Friction is the opposing force that comes into play when one body moves or tends to move over the surface of another body. Static friction self-adjusts up to a maximum limit, while kinetic friction acts during motion.
Dynamics of Circular Motion
Uniform circular motion requires a centripetal force directed towards the center of the circular path to continuously change the direction of velocity.
Important Formulas
Board Exam Info
In the CBSE Class 11 Physics exam, this chapter typically carries about 6 to 8 marks. Questions usually include a mix of 1-mark conceptual MCQs, 2-mark reasoning questions based on Newton's laws or inertia, and 3 to 5-mark numerical problems involving free-body diagrams, pulleys, inclined planes, and banking of roads.
Frequently Asked Questions
Do action and reaction forces cancel each other out?
No, action and reaction forces do not cancel each other because they act on two different bodies, not on the same body.
Why is static friction called a self-adjusting force?
Static friction automatically increases in magnitude to match the applied external force, up to a maximum limit called limiting friction, to keep the object at rest.
What is the primary role of a free-body diagram (FBD) in solving problems?
An FBD helps isolate a single body and visually represent all the real forces acting on it, making it much easier to apply Newton's second law along perpendicular axes.
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