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).
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 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 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 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 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
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