Class-11th Physics Ch-4 (Laws of Motion)

Class 11 Physics Laws of Motion notes

Laws of Motion Class 11 Notes Class 11 CBSE

Ch-4 Laws of Motion

Topic Covered

–Latest CBSE syllabus 2024-2025

-Introduction, Newton 1st, 2nd and 3rd Law,Momentum

-Conservation of Momentum, Impulse

-Friction, Free Body diagram, 

-Circular motion,Permitable speed on circular Motion

-Banking of Road

-Wear and Tear of Tyre.

-All types of Numericals Based on CBSE, JEE, NEET, and NDA. 

Class 11 Physics Laws of Motion notes

Dynamics is the area of physics where we examine how a body moves while accounting for the cause, or the force, behind the motion.

• Force
An external force, such as a push or pull, is what creates or attempts to create motion in a body that is at rest, stops or attempts to stop a moving body, or modifies or attempts to modify the body’s direction of motion.
• Inertia is the natural ability of a body to resist changes in its state of motion. The inertia increases with body weight; conversely, the inertia decreases with body weight.
According to the law of inertia, a body cannot independently alter its condition of rest, uniform motion (i.e., motion at a constant speed), or direction of motion.

• The Laws of Motion of Newton
Law 1: Until an external force is given to a body, it will either stay at rest or continue to move at a constant speed.
The “Law of inertia” is another name for the first law of motion. It defines the terms inertial frame of reference, force, and inertia.
To explain and comprehend particle motion, a “frame of reference” is always necessary. The most basic type of frame of reference that is employed is referred to as an inertial frame.
Any acceleration of a particle within an inertial frame, denoted by e, is attributed to the action of “real forces” on that particle.

Law 2 states that an acceleration produced by an external force acting on a body with a constant mass is directly proportional to the force and inversely proportional to the mass of the body.

Law 3 states that there is an equal and opposite reaction force to every action. Body B applies an equal and opposite force on body A in response to A exerting a force on it.

• Impulse (Class 11 Physics Laws of Motion notes)

Impulsive forces are defined as forces that act quickly. The product of force and the brief period that it acts is known as an impulse which play an important role in Class 11 Physics Laws of Motion notes.

A force’s impulse has a SI unit of 1 Nm and is a vector quantity.
— If an impulse’s force varies over time, its measurement involves determining the region bound by the force-time graph for that force. The entire change in the body’s momentum during a particular time is equal to the force’s impulse.

• Simultaneous Forces and Balance
“Concurrent forces are a set of forces acting simultaneously at one time.”
If the state of uniform motion or the position of the rest of the body under the action of concurrent forces does not alter, then the forces are said to be in equilibrium.
The resultant force of concurrent forces must be zero for them to be in equilibrium. If the three forces acting in a plane can be fully described by the three sides of a triangle taken in order, then the body will be in equilibrium. For equilibrium to occur, if there are more than three contemporaneous forces, these forces must be represented by the sides of a closed polygon.

• Frequently Employed Forces
I The mass of an organism. It is the force that draws an object towards the centre of the earth. The weight of the body is Mg in a vertically downward direction if M is the mass of the body and g is the acceleration caused by gravity.
Normal Force (ii). A contact force is created when two bodies come into contact; on smooth surfaces, the force’s direction is normal to the plane of contact. This force is known as the normal force.

(iii) A string’s tension. Let’s say there is a block suspended from a string. A force from the string balances the block’s weight because it is not moving but is acting downward vertically. The term “tension in string” refers to this force. A force in a stretched string is called tension. It moves away from the body under consideration and along the string.

• Apparent Weight and Actual Weight
— The “appearing weight” of a body is equivalent to its “actual weight” while it is moving uniformly or at rest.
— The apparent weight of a body for vertically upward accelerated motion is given as
Apparent weight =Actual weight + Ma = M (g + a)
— The apparent weight of a body for vertically downward accelerated motion is given as
Apparent weight = Actual weight Ma = M (g – a).

Friction (Class 11 Physics Laws of Motion notes)

Friction is the resistance to any relative motion between two surfaces that are in touch. It develops as a result of the two surfaces in contact’s surface imperfections “inter meshing.”
• Kinetic friction, both static and dynamic
Static friction refers to the frictional forces between two surfaces in contact (i) before and (ii) following the onset of a relative motion between them. There is usually a little bit more static friction than dynamic friction.
Additionally, the magnitude of the kinetic frictional force is proportional to the normal force.

• Limiting Frictional Force
This frictional force acts when the body is about to move. This is the maximum frictional force that can exist at the contact surface. We calculate its value using the laws of friction.

 Angle of Repose (Class 11 Physics Laws of Motion notes)

The angle of repose (α) is the angle of an inclined plane with the horizontal at which a body placed over it begins to slide down without any acceleration. The angle of repose is given by α = tan-1 (μ)