WORK AND ENERGY in 1 Shot || FULL Chapter Coverage (Concepts+PYQs) || Class 9th Physics

Physics Wallah Foundation・2 minutes read

Work in physics is defined as force causing displacement, with factors like angle, direction, and types of work, including gravitational and spring force, crucial in calculations and understanding energy transfer. Various forms of energy, such as potential, kinetic, and sound, play a role in demonstrating the Law of Conservation of Energy, with practical examples like a dam's potential energy conversion to electricity and power calculations illustrating energy transformation and transfer rates.

Insights

Work in physics is defined as force causing displacement, increasing energy in a body when done on it, and zero if either force or displacement is zero.
Understanding the angle between force and displacement is crucial for calculating work done, with special cases like theta = 0 degrees resulting in maximum work and theta = 90 degrees leading to zero work.
Energy, the capacity to do work, is obtained through food consumption, comes in various forms like chemical, heat, electric, light, and sound energy, and follows the Law of Conservation of Energy, where it can only be transferred or converted within a system.

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What is work in physics?
Force causing displacement.

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Summary

00:00

"Physics: Work, Energy, and Force Defined"

Work can be mental or physical, but in physics, work is defined as force causing displacement.
Spring force is negative when displacements are opposite.
Work increases energy in a body, while work done on a body decreases its energy.
Energy is the capacity to do work, and putting energy into a body means doing work on it.
Alok Chaubey welcomes viewers to the PW Foundation Channel for exam preparation.
The Sprint batch offers one-shot videos covering physics chapters like motion, force, gravity, and work.
Work is defined in physics as force multiplied by displacement.
Work is only done when a force is applied to an object causing displacement.
Work is zero if either force or displacement is zero.
Work is done when a force acts on a body causing it to displace from its initial position.

14:44

"Force, Displacement, and Work: Essential Concepts"

Inclined force applied leads to anger in the body, causing displacement of the child of the body.
Factors of force and displacement are crucial in understanding the situation.
Finding the angle between force and displacement is essential.
Horizontal and vertical components of force are significant in determining the effect on the box.
Net displacement of the box vertically is zero, emphasizing the horizontal component of force.
Calculation of work done involves the angle between force and displacement, denoted as theta.
Work done is maximum when force and displacement are in the same direction (theta = 0 degrees).
Work done is zero when force and displacement are perpendicular (theta = 90 degrees).
Negative work is done when force and displacement are opposite (theta = 180 degrees).
Understanding these special cases is crucial for calculating work done in various scenarios.

30:07

Circular Motion and Work: Essential Physics Concepts

Circular motion involves objects moving in a circular path, with displacement and velocity directions determined by tangents drawn at specific points.
Centripetal force is the force that keeps objects in circular motion, always directed towards the center of the circle.
The angle between displacement and force in circular motion is crucial, with a 90° angle indicating zero work done by the object.
Work done by a spring involves applying force to compress or expand it, with the work being negative when the spring opposes the external force.
The angle between spring force and displacement determines the work done, with the work always being negative due to the opposite directions of force and displacement.
Work done by the force of gravity is calculated by applying a force opposite to gravity's direction to displace an object upwards, with the work being negative due to the opposite directions of force and displacement.
Work done by a force of 7 Newton displacing a box from point A to point B is calculated as 56 Joules, with the unit of work done being Newton meter in the SI system.
The CGS unit of work done is erg, with 1 joule equaling 10^7 ergs.
Energy is essential for physical and mental activities, obtained through food consumption to replenish the body's energy levels.
Eating three meals a day is crucial to maintain energy levels for daily activities and prevent fatigue.

45:03

Forms and Functions of Energy Sources

Energy is defined as the capacity to do work, with more energy allowing for more work to be done.
Energy comes from doing work, and when work is done, energy is lost.
Different forms of energy include chemical, heat, electric, light, and sound energy.
Heat energy is used for cooking, warmth, and electricity generation.
Light energy allows us to see things, emitted by natural sources like the sun and artificial sources like electric bulbs.
Sound energy is associated with sound waves, emitted by objects like whistles and musical instruments.
Magnetic energy is present near magnets, attracting objects towards them.
Nuclear energy involves the fusion of two small nuclei into a larger one, releasing energy.
Kinetic energy is the energy possessed by a body due to its motion, calculated as 1/2 mv^2.
The work-energy theorem states that work done on an object equals the change in its kinetic energy, with the formula w = 1/2 m(v^2 - u^2) representing this relationship.

01:00:34

Energy and Work: Key Concepts Explained

Work Energy Theorem states that the work done on a body equals the change in kinetic energy.
The formula for kinetic energy is 1/2 * mass * velocity squared.
To increase the velocity of a car from 30 km/h to 60 km/h, work needs to be done.
The change in kinetic energy is equal to the work done on the body.
Potential energy is stored energy due to the position or confinement of an object.
Potential energy examples include a dam storing water for hydroelectric power generation.
Potential energy is also present in a stone on a hill or a compressed spring.
The Law of Conservation of Energy states that energy cannot be created or destroyed, only transferred or converted.
Potential energy can be calculated using the formula mass * acceleration due to gravity * height.
The potential energy of an object with a mass of 12 kg and a potential energy of 480 joules is at a height of 4 meters above the ground.

01:15:24

Energy Conservation and Transformation in Motion

The Law of Conservation of Energy states that energy cannot be created or destroyed in an isolated system.
Energy remains constant and only changes forms within the system.
Work is done when energy is used to displace an object, such as in the example of a bow and arrow.
Human energy is converted into potential energy when pulling back the arrow, which then transforms into kinetic energy upon release.
Kinetic energy can further convert into sound energy and heat due to friction, showcasing energy transformation.
Conservation of potential and kinetic energy is exemplified by an object's potential energy converting to kinetic energy as it falls and vice versa.
Mechanical energy, the sum of potential and kinetic energy, remains constant during motion.
The concept of power is defined as the rate at which work is done, measured in watts or horsepower.
Power is calculated by dividing work done by time, indicating the energy transfer rate.
Commercial units of power include watts and horsepower, with 1 kilowatt equaling 3.6 * 10^6 joules.

01:31:54

"Comparing Power: Girl A vs Girl B"

Girl A and Girl B, both with a weight of 400 Newtons, climb a height of 8 meters. Girl A takes 20 seconds to climb, while Girl B takes 50 seconds. Calculating their power, Girl A's power is 160 watts, and Girl B's power is 64 watts, indicating Girl A is more powerful.
The discussion transitions to power and energy, covering various forms of energy like potential and kinetic energy, the law of Conservation of Energy, and solving practice questions. The chapter concludes, hinting at the upcoming topic of sound in the next lecture.

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