CBSE Class 11 Physics Revision Notes Chapter 3

Class 11 Physics Revision Notes for Chapter 3 – Motion in a Straight Line

Learning Physics involves regular practice just like other subjects. Students often find Class 11 Physics to be challenging due to the complex terms, equations and laws in the chapters. To properly understand the topics, it is crucial for students to be familiar with the fundamental formulas and to regularly solve problems.

CBSE Class 11 Physics Chapter 3 Notes present complete information about the subject in a way that is brief and simple to understand. Extramarks offers concise, easily readable Class 11 Physics Chapter 3 Notes to aid students in revising the key topics before examinations.

1. Mechanics:

The study of how physical objects move is covered in the branch of physics known as mechanics.

It can be broadly divided into the branches below:

• Statics: This area of mechanics deals with the study of physical objects in a state of rest.
• Kinematics: This branch of mechanics studies how physical objects move without taking the causes of that movement into account.
• Dynamics: This branch of mechanics studies how physical objects move while taking the causes of that movement into account.

2. Rest And Motion

• Rest: 

When an object maintains its position in relation to its surroundings, it is said to be at rest.

For instance, the whiteboard in a classroom is at rest with regard to the classroom.

• Motion:

When an object shifts in relation to its surroundings, it is said to be in motion.

For instance, when we move relative to the ground while walking, running or riding a bike, we are said to be in motion.

• Rest and Motion are Relative:

Motion and rest depend on the observer. The same object might be in motion in one situation while it might be at rest in another.

For instance, the driver of a moving car is at rest in relation to a man (an observer) sitting in the passenger seat but is in motion in relation to an observer standing on the ground.

3. While Studying This Chapter:

• The objects would be regarded as point mass objects.
• If an object moves over distances that are significantly greater than its own size, it can be considered to have a point mass.
• We could limit our research to the study of rectilinear motion, or the movement of objects in straight lines.

4. Position, Distance, Displacement:

Position: An object’s position is always expressed in relation to some reference point, known as the origin. We take into account two physical quantities to express the change in position.

Distance: This is the actual path that an object travels while in motion. Its dimensions are [M0L1 T0] and its S.I. unit is ′m′.

Displacement: This term describes the variation between the final and initial positions of an object during motion.

Differences Between Distance and Displacement:

Distance:

• It describes the actual path taken by an object while in motion.
• It is a scalar quantity.
• When an object is moving, the distance it covers is always positive and never negative or zero.
• The distance travelled is always more than, or equal to the size of the displacement.
• The distance depends on the path taken by the object.

Displacement:

• It denotes the difference between the starting and ending positions.
• It is a vector quantity
• An object’s displacement during motion can be positive, negative or even zero.
• The amount of displacement is negligible or equal to the distance covered during motion.
• The magnitude of displacement is independent of the path travelled by an object during motion.

Difference Between Speed and Velocity:

Speed:

• It is defined as the total distance travelled divided by the amount of time that the motion has occurred.
• It is a scalar quantity.
• Throughout motion, it is always positive.
• It is more than or equal to the magnitude of the velocity.

Velocity:

• It describes the division of the time intervals during which a change in location or displacement takes place.
• It is a vector quantity
• During motion, it may be positive, negative or zero.
• It is equal to or less than the speed.

Note:

The amount of displacement is equal to the length of the entire path when an object is moving in a straight line and in the same direction.

In this instance, the average speed and average velocity are of equal magnitude. This isn’t always the case, though. The average velocity provides a general idea of an object’s speed over a period, but it does not provide information on the speed of the object at various points in that period.

5. Scalar and Vector Quantities:

Scalar Quantities

Scalar quantities are used to describe physical quantities that only have magnitude and no direction.

Scalars include things like mass, length, time, distance, speed, work and temperature, to name a few.

Vector Quantities

The term “vector quantity” refers to a physical quantity that has both magnitude and direction.

It includes displacement, velocity, acceleration, force, momentum and torque.

6. Average Velocity and Average Speed:

Average Velocity

The change in position or displacement divided by the time interval during which the displacement occurs is known as average velocity.

Average Speed

Average speed is calculated by dividing the total distance travelled by the total amount of time that the motion has occurred.

7. Instantaneous Velocity and Instantaneous Speed:

Instantaneous velocity:

• Instantaneous velocity is the speed at a specific moment t.
• The limit of average velocity at which the time interval t becomes infinitesimally small is another way to express instantaneous velocity.
• The amount on the right side of the previous expression is the differential coefficient of x with respect to t, and it is denoted by the symbol dx/dt.
• It refers to the rate of positional change in relation to the time at that specific moment.
• Its dimensions are [M0L1T-1] and its S.I. unit is m/s.

Instantaneous Speed:

• Instantaneous speed, also known as just speed, refers to the magnitude of velocity.
• Its dimensions are [M0L1T-1] and its S.I. unit is m/s.

8.Acceleration:

Average Acceleration:

The average acceleration during a period of time is defined as the change in velocity divided by the time interval.

The average change in velocity per unit of time is hence known as average acceleration.

It can be calculated mathematically as: 

a=(v2-v1)/(t2-t1),  where v2 and v1 are the velocities at time t2 and t1, respectively.

Its dimensions are [M0L1T-2] and its S.I. unit is m/s2.

Instantaneous Acceleration:

Instantaneous acceleration can be mathematically stated in the same way as instantaneous velocity, as seen below:

a=limΔt→0(v/t)=dv/dt

Its dimensions are [M0L1T-2] and its S.I. unit is m/s2.

Evidently, when there is uniform acceleration, instantaneous acceleration is equal to the average acceleration at that time. 

A change in velocity may also have an impact on one or both of these factors because velocity is a number that depends on both magnitude and direction. 

Therefore, changes in direction, speed (or magnitude), or both can result in acceleration. 

Similar to velocity, acceleration can also be zero, positive or negative. 

Note:

In this chapter, we would limit our focus to the investigation of constant acceleration. In this instance, the average acceleration is equivalent to the constant acceleration value over a given period of time. Acceleration is regarded as constant in all equations.

9. Graphs:

Uniform motion:

When a body travels the same distances over the same periods of time, it is said to be in uniform motion.

In this case, the speed remains constant throughout the movement.

In addition, during motion, there is no acceleration.

Non-Uniform motion:

A body is said to be in uniformly accelerated motion if its motion is uniform.

Here, the speed’s magnitude changes over time as it either rises or falls.

Additionally, given the accelerated motion, the acceleration would not be zero.

CBSE Class 11 Physics Notes Chapter 3 Motion in a Straight Line

Why Do You Need to Study CBSE Class 11 Physics Notes Chapter 3 Motion in a Straight Line?

Students will learn the fundamentals in CBSE Class 11 Physics Chapter 3 Notes Motion in a Straight Line, especially for those interested in building a career.

The Class 11 Physics Chapter 3 Notes from the CBSE are beneficial and entirely centred on the CBSE revised Syllabus.

1. Describe the situation in which the distance and displacement of a moving object are equal in size.
2. How can the distance travelled be calculated from a velocity-time graph?
3. What distinguishes motion in one, two and three dimensions?
4. Differences between:

• Displacement and Distance
• Velocity and speed

1. Give an example to illustrate the statement, “The direction in which an object moves is given by the direction of the item’s velocity and not by the direction of acceleration.”

CBSE Motion in Straight Line Class 11 Notes- Download

All students can easily access the Class 11 Physics Chapter 3 Notes which are available from Extramarks for a quick review of all the important equations and concepts right before the test. These notes were written by subject matter experts who are well-versed in the most recent NCERT curriculum and the format of the Class 11 exam. With Chapter 3 Physics Class 11 Notes, students can study well and obtain good marks on their tests.

These Notes Are Made Following the Latest CBSE Syllabus of Physics NCERT Books

1) Mechanics : 

• Statics
• Kinematics
• Dynamics

2) Rest and Motion 

• Defining Rest
• Defining Motion 
• Rest and motion as relative 

3) Defining Point/mass

4) Position, Distance Displacement 

5) Difference between : 

• Distance and Displacement 
• Speed and Velocity 
• Scalar and Vector Quantities 
• Average Velocity and Average Speed
•  Instantaneous Velocity and instantaneous speed

6) Acceleration 

7) Graphics 

8) Uniform Motion 

9) Non-Uniform Motion 

Conclusion

The Class 11 Physics Chapter 3 Notes are concise, well-structured and in simple language. All of the topics have been thoroughly covered by subject matter experts. Access the Extramarks Class 11 Physics Chapter 3 Notes for a quick revision before the test. These notes are a great way to prepare for exams and will help students in understanding various concepts related to the chapter.