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NCERT Class 11 Physics Chapter 5 Notes Laws of Motion - Download PDF

NCERT Class 11 Physics Chapter 5 Notes Laws of Motion - Download PDF

Edited By Vishal kumar | Updated on Jan 30, 2024 03:11 PM IST

In the ever-changing landscape of academic examinations such as boards, state exams, and competitive tests like JEE or NEET, effective study materials are critical to success. Law of Motion class 11 notes provide crucial insights, and Careers360's meticulously crafted notes are a game changer. These CBSE class 11 physics ch 5 notes, prepared by subject experts, are not only comprehensive but also available in both online and offline PDF formats, giving students more flexibility in their study methods.

These class 11 physics chapter 5 notes simplify the learning process by emphasising clarity and precision, making the complex principles of motion more accessible. In the time-sensitive context of exam preparation, the Careers360 Class 11 Physics Chapter 5 notes are an invaluable resource, offering an efficient and strategic path to understanding and mastering the Law of Motion. Don't just study; use Careers360's expertly designed ch 5 physics class 11 notes to accelerate your success in Chapter 5.

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Forces in touch and non-contact

Forces are important in the dynamics of motion because they influence how bodies start, stop, and change states. When we examine forces, we can divide them into two categories: contact forces and non-contact forces.

Contact forces are generated when an external force physically touches the body. A classic example of contact force is the impact of a bat hitting a cricket ball during a cricket match. The force is transferred from the bat to the ball via direct physical contact.

Non-contact forces, on the other hand, do not make direct physical contact with the body. Magnetic force is an excellent example of non-contact force. When a magnet is near a coin, the coin is drawn to the magnet without making any visible physical contact. This demonstrates the influence of forces even in the absence of direct contact, emphasising the fascinating nature of non-contact forces in the realm of Physics.

For example, consider a ball rolling across the floor. Aristotle's theory suggests that a constant force be applied to keep it moving. However, the ball will eventually come to a stop due to friction. Friction acts as a counterforce, gradually slowing and eventually stopping the ball's motion, allowing for a thorough understanding of both motion initiation and cessation. Aristotle's fallacy serves as a reminder of the evolving nature of scientific understanding, as well as the importance of taking into account all aspects of a phenomenon.


Inertia is a body's resistance to changes in motion. Objects at rest tend to remain at rest, whereas moving objects strive to maintain motion. This principle describes the natural tendency of objects to resist changes in velocity, whether they are stationary or moving.

  • Inertia is not a physical quantity but a property of a body, contingent on its mass.
  • Unlike traditional physical quantities, inertia doesn't have units and dimensions.
  • Two bodies of equal mass have the same inertia, whether they are in motion or at rest. Inertia is a mass-dependent factor that does not change with velocity.

Galileo's Inertia Law

Galileo's Inertia Law transformed our understanding of motion, establishing Aristotle's theories. Galileo asserted that an external force is only required to sustain motion when resistive forces, such as friction, are present. This correction challenged the earlier belief that a constant force was required to maintain motion, signalling a significant departure from Aristotle's ideas and paving the way for a more accurate understanding of inertia and motion.

Newton’s First law of motion

Newton's First Law states that unless acted upon by an external force, a body will remain at rest or in uniform motion along a straight line. This law describes the concept of inertia, which takes many forms.

  1. If no net force affects a body, its velocity remains constant and acceleration is impossible. This principle emphasises the idea that an external force is required for motion changes.
  2. Newton's first law is appropriately known as the law of inertia because it defines this property. Inertia is classified into three types: inertia at rest, inertia in motion, and inertia of direction.
  3. The term "inertia of rest" refers to a body's resistance to change its state of rest on its own. Basically, a body at rest remains in that state and does not move spontaneously. This emphasises the inherent tendency of objects to maintain their current state unless influenced by external forces.
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Balanced and Unbalanced Forces

Balanced forces are defined as equal forces acting in diametrically opposed directions. In this scenario, the object's motion remains constant. An apt analogy is a tug of war, in which teams exert equal forces in opposite directions, resulting in equilibrium.

On the other hand, unbalanced forces involve unequal forces acting in the same or opposite directions. These forces cause alterations in the object's motion or shape. Returning to the tug-of-war example, an imbalance occurs when Team 1 exerts more force than Team 2. As a result, Team 1 wins due to favourable net movement. This scenario exemplifies an unbalanced force, demonstrating how variations in force magnitude affect the outcome.

Linear Momentum

Linear momentum (p) is a vector quantity that is obtained as the product of an object's mass (m) and velocity (v). The linear momentum formula is expressed as follows:1705547690386

  • Units: kg-m/sec [S.I.], g-cm/sec [C.G.S.]
  • Dimension: [MLT-1]
  • When two objects of different masses have the same momentum, the lighter body has a higher velocity.


Newton’s Second Law of Motion

The law states that the rate of change of linear momentum of a body is directly proportional to the external force applied to the body, and this change in momentum always occurs in the direction of the applied force.

If a body of mass (m) is moving with velocity (v), then its linear momentum p is given by the product of its mass and velocity and if Force (f) is applied to the body then,

\begin{array}{ll} & \vec{F} \propto \frac{d \vec{p}}{d t} \Rightarrow F=K \frac{d \vec{p}}{d t} \\ & \vec{F}=\frac{d \vec{p}}{d t} \\ \text { or } \quad & \vec{F}=\frac{d}{d t}(m \vec{v})=m \frac{d \vec{v}}{d t}=m \vec{a} \quad\left(\text { from } a=\frac{d \vec{v}}{d t}\text {}\right) \\ \\ \text { or } \\ \quad \vec{F}=m \vec{a} \\ \\ \therefore \quad & \text { Force }=\text { mass } \times \text { acceleration }\end{array}


An impulsive force occurs when a strong force acts on an object for just a short amount of time. Unlike a steady force, an impulsive force rapidly increases from zero to its maximum value and then returns to zero. In these cases, we evaluate the force's overall impact on the object.


  • Impulse is a vector quantity, so it has both magnitude and direction. Its direction corresponds to the direction of the force applied.
  • Dimension of impulse: [MLT-1]
  • SI unit- Newton-second or Kg-m-s-1 and CGS unit- Dyne-second or gm-cm-s-1

Newton’s Third Law of Motion

Newton's Third Law of Motion states, that every action has an equal (in magnitude) and opposite (in direction) reaction.

Newton's Third Law states that if FAB represents the force exerted on body A by body B (action) and FBA represents the force exerted on body B by body A (reaction), then FAB = -FBA

Laws of Conservation of Momentum

According to the Law of Conservation of Linear Momentum, when no external forces act on an isolated system, its total linear momentum remains constant. In other words, the total momentum of a closed system of interacting objects remains constant over time, assuming no external forces influence it.

According to this law, 1705552013789

In the absence of external forces, If F equals 0, then p is constant.

i.e, Psystem= P1+ P2+ P3+ P4+ ..........= constant


Friction is a force that occurs at the point of contact between two surfaces and works to oppose relative or approaching motion between them.

Friction can be categorized into three main types:

  • Static Friction: Acts on stationary objects, preventing them from initiating motion. The force of static friction increases with the applied force until motion is initiated.
    fs µsN
  • The maximum static frictional force (fs)max= µsN
  • Kinetic friction: Kinetic friction is the force that arises between two surfaces when they are moving relative to one another.

    The kinetic frictional force (fk) is proportional to the normal force (N) and can be expressed as fk = µk N

  • Rolling friction: Rolling friction is the force that opposes the motion of an object as it rolls across a surface. It occurs when there is relative motion between the surface and the part of the object that makes contact with it. it is similar to kinetic friction.

Circular Motion

  • Angular Displacement(θ): The angular displacement of an object moving around a circular path is defined as the angle traced out by the radius vector at the centre of the circular path over time. This is a vector quantity.

θ= s/r, where s is the arc length and r is the radius.

  • Angular Velocity (ω): The angular velocity of an object in circular motion is defined as the rate at which its angular displacement changes over time.

ω= Δθ/Δt, where Δθ is the change in angular displacement, and Δt is the change in time.

  • Angular Acceleration (α): The angular acceleration of an object in circular motion is defined as the rate at which its angular velocity changes over time.

α= Δt/Δω, where Δω is the change in angular velocity, and Δt is the change in time

  • Uniform Circular Motion: Uniform circular motion occurs when a point object moves along a circular path at a constant speed.

    In this type of motion, the speed remains constant while the direction changes continuously, resulting in circular motion.

ac=v2/r, where r is the radius

Key Features of Physics Class 11 Chapter 5 Notes PDF

  1. Accessibility and Portability: Law of Motion class 11 notes are portable and easily accessible on digital devices such as laptops, tablets, and smartphones. This portability allows students to review the material at any time and from any location.
  2. Structured Content: Law of Motion notes class 11 in PDF format are usually well-organized and structured, allowing students to follow the chapter's topic sequence.
  3. visual Aids and Diagrams: PDF notes include visual aids such as diagrams and illustrations to help students understand. Visual representations of concepts can be particularly useful in physics.
  4. Printable: Students can print the CBSE class 11 physics ch 5 notes, allowing them to keep a physical copy for offline reference. This is useful for those who prefer to study with hard copies.
  5. Consistency and Accuracy: Ch 5 Physics Class 11 notes a consistent and accurate representation of the content. The format remains the same regardless of the device or software used to open the file.

Significance of NCERT Class 11 Physics Chapter 5 Notes

Class 11 Laws of Motion notes offer a comprehensive review of the chapter, emphasizing key concepts aligned with the CBSE Physics Syllabus in Class 11. These NCERT Class 11 Physics Chapter 5 notes are not only valuable for board exams but also serve as a useful resource for competitive exams like VITEEE, BITSAT, JEE Main, NEET, and more. With the convenience of offline access through PDF downloads, these notes ensure effective study sessions even when internet connectivity is unavailable.

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Frequently Asked Question (FAQs)

1. What do you mean by Friction according to Class 11 Physics chapter 5 notes?

Friction, as explained in Class 11 Physics Chapter 5 notes, is the force that opposes relative motion between surfaces and comes into play when an external force is applied.

2. What is Newton’s Third Law ?

Newton's Third Law of Motion states that for every action, there is an equal (in magnitude) and opposite (in direction) reaction. In other words, the forces of interaction between two objects are always equal and act in opposite directions.

3. What is Inertia?

Inertia is the resistance of an object to changes in its state of motion. It reflects the tendency of a stationary object to stay at rest and a moving object to continue moving with a constant velocity unless acted upon by an external force.

4. What is Impulse?

Inertia is the resistance of an object to changes in its state of motion. It reflects the tendency of a stationary object to stay at rest and a moving object to continue moving with a constant velocity unless acted upon by an external force.

5. What do you understand by Kinetic Friction?

Kinetic friction is the force resisting motion between surfaces, occurring when two objects slide against each other, and its magnitude is proportional to the normal force.

6. Is physics class 11 chapter 5 notes pdf important for JEE?

Yes, Physics Class 11 Chapter 5 notes in PDF are important for JEE (Joint Entrance Examination) preparation. These notes cover fundamental concepts in Newton's Laws of Motion, a crucial topic for JEE, providing a comprehensive resource for understanding and revising key principles.

7. What is the significance of this chapter for the CBSE board test, and how may these Class 11 Laws of Motion notes help?

From the notes for Class 11 Physics Chapter 5, students can expect 4 to 6 mark questions, and they can use this note for quick revision to help them improve their grades.


Get answers from students and experts

A block of mass 0.50 kg is moving with a speed of 2.00 ms-1 on a smooth surface. It strikes another mass of 1.00 kg and then they move together as a single body. The energy loss during the collision is

Option 1)

0.34\; J

Option 2)

0.16\; J

Option 3)

1.00\; J

Option 4)

0.67\; J

A person trying to lose weight by burning fat lifts a mass of 10 kg upto a height of 1 m 1000 times.  Assume that the potential energy lost each time he lowers the mass is dissipated.  How much fat will he use up considering the work done only when the weight is lifted up ?  Fat supplies 3.8×107 J of energy per kg which is converted to mechanical energy with a 20% efficiency rate.  Take g = 9.8 ms−2 :

Option 1)

2.45×10−3 kg

Option 2)

 6.45×10−3 kg

Option 3)

 9.89×10−3 kg

Option 4)

12.89×10−3 kg


An athlete in the olympic games covers a distance of 100 m in 10 s. His kinetic energy can be estimated to be in the range

Option 1)

2,000 \; J - 5,000\; J

Option 2)

200 \, \, J - 500 \, \, J

Option 3)

2\times 10^{5}J-3\times 10^{5}J

Option 4)

20,000 \, \, J - 50,000 \, \, J

A particle is projected at 600   to the horizontal with a kinetic energy K. The kinetic energy at the highest point

Option 1)


Option 2)

\; K\;

Option 3)


Option 4)


In the reaction,

2Al_{(s)}+6HCL_{(aq)}\rightarrow 2Al^{3+}\, _{(aq)}+6Cl^{-}\, _{(aq)}+3H_{2(g)}

Option 1)

11.2\, L\, H_{2(g)}  at STP  is produced for every mole HCL_{(aq)}  consumed

Option 2)

6L\, HCl_{(aq)}  is consumed for ever 3L\, H_{2(g)}      produced

Option 3)

33.6 L\, H_{2(g)} is produced regardless of temperature and pressure for every mole Al that reacts

Option 4)

67.2\, L\, H_{2(g)} at STP is produced for every mole Al that reacts .

How many moles of magnesium phosphate, Mg_{3}(PO_{4})_{2} will contain 0.25 mole of oxygen atoms?

Option 1)


Option 2)

3.125 × 10-2

Option 3)

1.25 × 10-2

Option 4)

2.5 × 10-2

If we consider that 1/6, in place of 1/12, mass of carbon atom is taken to be the relative atomic mass unit, the mass of one mole of a substance will

Option 1)

decrease twice

Option 2)

increase two fold

Option 3)

remain unchanged

Option 4)

be a function of the molecular mass of the substance.

With increase of temperature, which of these changes?

Option 1)


Option 2)

Weight fraction of solute

Option 3)

Fraction of solute present in water

Option 4)

Mole fraction.

Number of atoms in 558.5 gram Fe (at. wt.of Fe = 55.85 g mol-1) is

Option 1)

twice that in 60 g carbon

Option 2)

6.023 × 1022

Option 3)

half that in 8 g He

Option 4)

558.5 × 6.023 × 1023

A pulley of radius 2 m is rotated about its axis by a force F = (20t - 5t2) newton (where t is measured in seconds) applied tangentially. If the moment of inertia of the pulley about its axis of rotation is 10 kg m2 , the number of rotations made by the pulley before its direction of motion if reversed, is

Option 1)

less than 3

Option 2)

more than 3 but less than 6

Option 3)

more than 6 but less than 9

Option 4)

more than 9

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