Category: NCERT PDF NOTES CLASS 9

Chapter 12 of the class 9 science textbook typically covers the topic of sound. Some of the main concepts that may be covered in this chapter include:

The nature of sound and how it travels as a wave
The properties of sound waves, such as frequency, amplitude, and wavelength
The speed of sound in different mediums and how it is affected by temperature and pressure
The human ear and how it perceives sound
The production, propagation, and reception of sound
Acoustics and architectural acoustics
Ultrasound and its uses in medicine and industry
Noise pollution and its effects on health and the environment

Some of the key terms that may be discussed in this chapter include:

Sound wave
Frequency
Amplitude
Wavelength
Pitch
Loudness
Eardrum
Cochlea
Ultrasound
Decibel
Noise pollution
This is just a general overview of what might be covered in a class 9 science chapter 12 on sound, and the specific content may vary depending on the textbook and curriculum being used.

Sound

• The sensation felt by our ears is called Sound.
• A sound is a form of energy that makes us hear.
• Sound travels in form of waves.

Characteristics of Sound waves

The characteristics of sound waves are:- Wavelength, Frequency, Amplitude, Time period, and Velocity.

Wavelength of Sound waves

The distance between two consecutive identical points on a wave is known as the Wavelength of that soundwave. For example, the distance between two consecutive peaks or two consecutive troughs of a wave is one wavelength. It is a measure of how long the wave is. The wavelength is often represented by the Greek letter lambda (λ) and is measured in units of distance such as meters (m) or centimeters (cm).

Frequency of Sound

Amplitude of Sound

Time period

Velocity of Sound

Class 9 science Chapter: 11:- Work and Energy

Class 9 science Chapter: 13:- Why do we fall ill?

Chapter 11 in class 9 science typically covers the topic of work and energy. The chapter may include information on the concepts of work, energy, power, potential energy, kinetic energy, and conservation of energy. It may also cover different types of energy such as mechanical, thermal, chemical, nuclear, and electrical energy. Additionally, the chapter may discuss examples and applications of work and energy in real-world scenarios, such as in machines, engines, and power generation.

The PDF Notes of Class 9 Science Chapter 11 :- Work and Energy is Here

Definition of Work

Work is defined as the amount of energy transferred or transformed when an object is moved by an external force through a distance. Mathematically, work is represented as the product of the force applied and the distance moved in the direction of the force. The unit of work is Joules (J) in the International System of Units (SI).

Workdone

The work is said to be done when :

• a moving object comes to rest
• an object at rest starts moving
• velocity of an object changes
• shape of an object changes

Energy

Energy is the ability to do work. It is a property of an object or system that can be transferred or transformed, but not created or destroyed. Energy can exist in various forms, including kinetic energy (energy of motion), potential energy (energy of position), thermal energy (energy of heat), chemical energy (energy stored in the bonds of molecules), and electrical energy (energy of moving electric charges). The unit of energy is also Joules (J) in the International System of Units (SI).
The Law of Conservation of energy states that energy cannot be created or destroyed, it can only be transferred or converted from one form to another.

Mechanical Energy

Mechanical energy is the sum of kinetic energy and potential energy in an object or system
For example, a roller coaster at the top of a hill has potential energy due to its position, and as it descends, it converts that potential energy into kinetic energy of motion.

Kinetic energy

Kinetic energy is the energy that an object possesses due to its motion. It is defined as the work required to accelerate an object of a given mass from rest to its current velocity. Mathematically, kinetic energy can be represented by the equation:

KE = 1/2 * m * v^2

Where KE is the kinetic energy, m is the mass of the object and v is the velocity of the object.
The unit of kinetic energy is Joules (J) in the International System of Units (SI).
It’s important to note that the kinetic energy of an object increases as its velocity increases and vice-versa. Also an object at rest has zero kinetic energy

For example :-

• A moving cricket Ball
• Running water
• A moving bullet
• Flowing Mind
• A running Athlete
• A rolling Stone

Potential Energy

Potential energy is the energy that an object possesses due to its position or shape. It is the energy stored within an object due to the forces acting upon it. The potential energy of an object depends on its position in a force field, for example, due to gravity or due to a spring.
There are different types of potential energy:

Gravitational potential energy is the energy an object possesses due to its height above a reference point, such as the ground. It is the energy that an object has due to its position in a gravitational field.
Elastic potential energy is the energy stored in an object as the result of deformation, such as a stretched or compressed spring.
Chemical potential energy is the energy stored in the bonds between atoms or molecules.
Nuclear potential energy is the energy stored in the nucleus of an atom.
The unit of potential energy is also Joules (J) in the International System of Units (SI).
It’s important to note that the potential energy of an object increases as it is raised to a higher position, and decreases as it is lowered

The PDF Notes of next Chapter :-

Class 9 Science chapter – 12 : Sound

Class 9 Science chapter 10, Gravitation, introduces students to the concept of gravitation and its effects on objects. The chapter covers topics such as the law of gravitation, gravitational force, weight, and the gravitation of celestial bodies. It also covers the application of these concepts in real-world scenarios, such as the motion of planets and satellites, and the tides. The chapter aims to help students understand the fundamental principles of gravitation. Andhow they can be applied to explain the behavior of objects in the world around them.

The topics that we are going to understand in this Chapter are :-

• The law of gravitation, including the formula and its derivation
• The gravitational force between two objects and its relationship to mass and distance
• The gravitation of celestial bodies, such as planets and satellites, and their orbits
• The tides and their causes
• The escape velocity and its applications
• The fundamental principles of gravitation and how it affects the motion of objects in the world around them

Gravitation

Gravitation is the force of attraction between any two objects in the universe. It is one of the four fundamental forces of nature, along with electromagnetism, the weak nuclear force, and the strong nuclear force. The force of gravitation is proportional to the product of the masses of the two objects and inversely proportional to the square of the distance between them. This relationship is known as the law of gravitation, which was first proposed by Sir Isaac Newton in his laws of motion. The formula for the law of gravitation is:

F = G (m1 * m2) / r^2

1. Where,
2. F is the force of gravitation,
3. G is the gravitational constant,
4. m1 and m2 are the masses of the two objects, and
5. r is the distance between their centers of mass.

The same formula is written in the PDF Notes of Class 9 Science Gravitation. PDF Notes are Give Above.

Gravity is the force that attracts objects towards the center of the Earth, or any other celestial body. This is why objects fall towards the ground when dropped. The force of gravity also keeps the planets in orbit around the sun and the moon in orbit around the Earth.

Law of Universal Gravitation

Newton’s Universal Law of Gravitation, also known as the law of gravitation, is a scientific law that states that every point mass in the universe attracts every other point mass with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them. The formula for the law of gravitation is:

F = G (m1 * m2) / r^2

Where F is the force of gravitation, G is the gravitational constant, m1 and m2 are the masses of the two objects, and r is the distance between their centers of mass.

The law of gravitation was first proposed by Sir Isaac Newton in 1687 and is considered one of his laws of motion. It is a fundamental law of physics and applies to all objects in the universe, from subatomic particles to galaxies. The law can be used to calculate the gravitational force between two objects and also to explain the motion of celestial bodies such as planets and satellites.

Newton’s law of gravitation helps to explain the motion of celestial bodies in the solar system. The motion of a projectile under the influence of gravity. It also helped to explain the observed motion of the planets and the moon, which had long been a mystery.

Next Chapter of Class 9 Science :-

Chapter – 11 :- Work and Energy

Class 9 Science chapter 9, Forces and Laws of Motion, introduces students to the concept of force and its various forms. The chapter covers topics such as contact and non-contact forces, balanced and unbalanced forces, friction, and laws of motion. The chapter also covers the application of these concepts in real-world scenarios, such as the motion of objects under the influence of forces, and the motion of projectiles.

Some of the specific topics that are likely to be covered in this chapter include:

• Definition and types of force
• The concept of balanced and unbalanced forces
• Friction and its effects on motion
• Newton’s laws of motion and their applications
• The effect of force on the motion of objects
• Gravitational force and weight
• The concept of action and reaction forces

The chapter aims to help students understand the fundamental principles of force and how they can be applied to explain the behavior of objects in the world around them.

Forces

A force is a push or pull upon an object resulting from the object’s interaction with another object. Forces can cause an object to accelerate, change direction, or stay in motion. A force is a vector quantity, meaning it has both magnitude and direction. The unit of force in the International System of Units (SI) is the newton (N).

There are several types of forces, including:

• Contact forces: result from the physical contact between two objects, such as friction, tension, normal force, and air resistance.
• Non-contact forces: result from the interaction of two objects without physical contact, such as gravity, magnetism, and electric force.
• Balanced forces: forces that cancel each other out, resulting in no acceleration or change in motion of an object.
• Unbalanced forces: forces that do not cancel each other out, resulting in acceleration or change in motion of an object.
• Forces can be represented graphically using force diagrams, which show the direction and relative magnitude of the forces acting on an object

Next Chapter :- Chapter – 10 Gravitation

Class 9 Science chapter 8, Motion, introduces students to the concept of motion and its various forms. The chapter covers topics such as distance and displacement, speed and velocity, acceleration, and laws of motion. It also covers the application of these concepts in real-world scenarios. Such as the motion of objects under the influence of forces and the motion of projectiles. The chapter Aims to help the students to understand the fundamental principles of motion and how they can be applied to explain the behavior of objects in the world around them.

In class 9 science chapter – 8 Motion the students are going to understand the following topics:-

Motion

Motion is the change in position of an object with respect to its surroundings in a given period of time. A body is in motion if it changes its position continuously with reference to the point. Objects can be in motion relative to a reference point or frame of reference. For example, a car moving along a road would be in motion relative to the road, while a person riding in the car would be in motion relative to the car. Motion can be of different types depending upon the type of path by which the object is going through.

Scalar and Vector Quantity

A scalar quantity is a physical quantity that is described by a single value, such as distance, time, or mass. Scalar quantities do not have any direction associated with them. For example, distance is a scalar quantity because it is simply a measure of how far apart two points are, regardless of the direction of the distance.

On the other hand, a vector quantity is a physical quantity that is described by both a value and a direction. Examples of vector quantities include velocity, acceleration, and force. These quantities have a magnitude and a direction. For example, velocity is a vector quantity because it is described by both the speed of an object and the direction it is moving in.

Distance and Displacement

• The actual path or length travelled a object during its journey from initial position to final position is called its Distance.
• Distance is a scalar quantity.

Displacement is a vector quantity that represents the change in position of an object. It is defined as the distance and direction between the initial and final position of an object. It is a measure of how far an object has moved from its starting point, regardless of the path taken. The displacement vector points from the initial position to the final position of an object. For example, if a car moves from point A to point B, its displacement is the vector pointing from point A to point B.

Uniform Motion

Uniform motion is a type of motion in which an object moves at a constant speed in a straight line. In other words, the velocity of an object in uniform motion is constant and does not change over time. If an object is in uniform motion, the distance traveled and the time taken to travel that distance are directly proportional. This means that the object covers equal distances in equal intervals of time.

In contrast, non-uniform motion is a type of motion in which an object’s speed changes over time. This can happen when an object is accelerating (speeding up) or decelerating (slowing down).

Non-Uniform Motion

Non-uniform motion is a type of motion in which an object’s velocity changes over time. This means that the speed of the object is not constant and can either be increasing or decreasing. It can be further classified into two types of non-uniform motion: acceleration and deceleration.

Acceleration is a change in velocity, where an object’s speed is increasing over time. This can be caused by a net force acting on the object or by a change in the direction of its velocity. For example, a car accelerating from a stop sign is in non-uniform motion.

Deceleration is the opposite of acceleration, it is a change in velocity where an object’s speed is decreasing over time. This can be caused by a net force acting on the object in the opposite direction. For example, a car slowing down to a stop is in non-uniform motion.

In non-uniform motion, the distance traveled and the time taken to travel that distance are not directly proportional, unlike uniform motion.

After reading this chapter you can go through the next chapter of class 9 Science. Link is given below :-

Chapter – 9 :- Force and Laws of Motion