Grade 9
  1. Mechanics  1.1. Motion  1.1.1. Types of motion  1.1.2. Distance and displacement  1.1.3. Speed and Velocity  1.1.4. Acceleration  1.1.5. Graphical representation of motion  1.1.6. Equations of motion  1.1.7. Uniform and non-uniform motion  1.1.8. Free fall and acceleration due to gravity  1.1.9. Relative speed  1.1.10. Circular motion  1.2. Laws of force and motion  1.2.1. The concept of force  1.2.2. newton's first law of motion  1.2.3. Newton's second law of motion  1.2.4. Newton's third law of motion  1.2.5. Inertia and types of inertia  1.2.6. Motion  1.2.7. Conservation of momentum  1.2.8. Application of Newton's laws in daily life  1.2.9. Types of Forces (Contact and Non-Contact)  1.2.10. Friction and its effects  1.3. Gravitational force  1.3.1. Newton's law of universal gravitation  1.3.2. Importance of Gravitational Force  1.3.3. Acceleration due to gravity  1.3.4. Free fall and weightlessness  1.3.5. Mass and weight  1.3.6. Variation of g with height and depth  1.3.7. Kepler's laws of planetary motion  1.3.8. Satellites and their orbits  1.4. Work, Energy and Power  1.4.1. Concept of work  1.4.2. Positive and negative actions  1.4.3. Work done by constant and variable force  1.4.4. Energy and its forms  1.4.5. Kinetic energy and potential energy  1.4.6. Law of conservation of energy  1.4.8. Commercial unit of energy  1.4.9. Work–energy theorem  1.5. Simple machines  1.5.1. Types of simple machines  1.5.2. Mechanical advantage  1.5.3. Machine efficiency  1.5.4. Levers and their types  1.5.5. Pulleys and Inclined Planes  1.5.6. Gears and their uses
  2. Properties of matter  2.1. States of matter  2.1.1. Solids, liquids and gases  2.1.2. Properties of different states of matter  2.1.3. Change in state of matter  2.1.4. Plasma and Bose–Einstein condensate  2.2. Density and pressure  2.2.1. Concept of density and relative density  2.2.2. Pressure in solids, liquids and gases  2.2.3. Pascal's law and its applications  2.2.4. Atmospheric pressure and its variations  2.2.5. Surface tension and capillarity  2.3. Buoyancy and Archimedes' principle  2.3.1. Buoyant force  2.3.2. Archimedes principle  2.3.3. Applications of Archimedes' Principle  2.3.4. floating and sinking objects  2.3.5. Theory of Flotation and Archimedes' Principle
  3. Heat and Thermodynamics  3.1. Temperature and heat  3.1.1. Concept of heat and temperature  3.1.2. Temperature measurement  3.1.3. Temperature scales  3.2. Heat transfer  3.2.1. Conduction of heat  3.2.2. Convection of heat  3.2.3. heat radiation  3.2.4. Applications of heat transfer  3.2.5. Thermal conductivity  3.3. Thermal expansion  3.3.1. Expansion of solids, liquids and gases  3.3.2. Abnormal expansion of water  3.3.3. Applications of Thermal Expansion  3.4. Specific heat capacity and latent heat  3.4.1. Concept of specific heat capacity  3.4.2. Measurement and applications of specific heat  3.4.3. Latent heat of fusion and vaporization  3.4.4. Heat Engines and Efficiency
  4. Waves and sound  4.1. Waves and their types  4.1.1. Mechanical and electromagnetic waves  4.1.2. Longitudinal and Transverse Waves  4.1.3. Properties of Waves  4.1.4. Wavelength, frequency and speed of the wave  4.1.5. Superimposition of waves  4.2. Sound waves  4.2.1. Nature and transmission of sound  4.2.2. Speed of sound in different mediums  4.2.3. Reflection of sound and echo  4.2.4. Sonar and ultrasound  4.2.5. Resonance and pulsation  4.3. Sound characteristics  4.3.1. Intensity, loudness and quality of sound  4.3.2. Doppler effect in sound
  5. Lighting and Optics  5.1. Reflection of light  5.1.1. Laws of reflection  5.1.2. Reflection from a plane mirror  5.1.3. Reflection from a spherical mirror  5.1.4. Image formation by concave and convex mirrors  5.1.5. Applications of Reflection  5.2. Refraction of light  5.2.1. Laws of refraction  5.2.2. Refractive index  5.2.3. Refraction through a glass slab  5.2.4. Refraction in water and air  5.2.5. Lenses and their types  5.2.6. Image formation by convex and concave lenses  5.2.7. Total internal reflection and its applications  5.3. Dispersion and scattering of light  5.3.1. Spectrum of white light  5.3.2. Prisms and Dispersion  5.3.3. Tyndall effect and blue sky
  6. Electricity and Magnetism  6.1. Electric charge and static electricity  6.1.1. The concept of electric charge  6.1.2. Charging by friction, contact and induction  6.1.3. Electroscope and its working  6.2. Current Electricity  6.2.1. The concept of electric current  6.2.2. Ohm's Law and Resistance  6.2.3. Factors affecting resistance  6.2.4. Series and Parallel Circuits  6.2.5. Heating effect of electric current  6.2.6. Electric power and energy  6.3. Magnetism  6.3.1. Natural and artificial magnets  6.3.2. Properties of magnets  6.3.3. Earth's magnetism  6.3.4. Magnetic field and field lines  6.3.5. Electromagnets and their applications
  7. Modern Physics  7.1. structure of the atom  7.1.1. Atomic Structure and Subatomic Particles  7.1.2. Electrons, Protons, and Neutrons  7.1.3. Rutherford and Bohr model  7.2. Radioactivity  7.2.1. Types of radioactive emissions  7.2.2. Half-life and radioactive decay  7.2.3. Uses and Hazards of Radioactivity
  8. Space science and astronomy  8.1. The universe and its components  8.1.1. Stars and galaxies  8.1.2. Planets and Solar System  8.2. Satellites  8.2.1. Natural and artificial satellites  8.2.2. Use of satellites

Grade 9 → Mechanics ↓


Work, Energy and Power


Introduction to the work

In the world of physics, "work" has a specific meaning. It may sound similar to how we use the word in everyday language, but in physics, it has a unique definition. Work is done when a force is applied to an object and the object moves as a result of that force.

What is the work?

Work is defined as the force applied to an object multiplied by the distance over which the force is applied. The formula for work is:

    Work (W) = Force (F) × Distance (d)

Work is measured in a unit called joule (J). One joule is the work done when a force of one newton moves an object forward one metre.

When is the work completed?

Work is done only when the component of the force is in the direction of motion. For example, if you push a book across a table, you are doing work on the book because your force moves it a certain distance. However, if you move the book, at a constant speed, horizontally from one place to another, you may feel like you are doing hard work, but in terms of physics, you are not doing any work holding the book horizontally, because the applied force (upward) does not cause horizontal motion.

Examples of work

Let's look at some simple examples of work:

Example 1: Pushing a car

Consider pushing a car stuck in mud. If you apply a force of 100 N and the car moves 2 m, the work you have done is:

    Work = 100 N × 2 m = 200 J

Example 2: Carrying a suitcase

If you lift a suitcase from the ground with a force equal to its weight (20 N) and lift it 1.5 m up, the work done will be:

    Work = 20 N × 1.5 m = 30 J

Example 3: No work done

Imagine you are pushing a wall. You can apply force, but if the wall does not move, the distance is zero. Therefore, no work is done:

    Work = Force × 0 = 0 J

Visual example

Force Direction of force

This diagram shows the use of force to move an object. The rectangle represents the object that is being pushed.

Understanding energy

Energy, just like work, is a fundamental concept in physics. Energy is often defined as the ability to do work. There are different forms of energy, including kinetic energy, potential energy, thermal energy, and more.

Kinetic energy

Kinetic energy is the energy an object has because of its motion. The formula for kinetic energy (KE) is:

    KE = 0.5 × mass (m) × velocity (v) 2

An object in motion has kinetic energy. For example, a moving car, flowing water, or a flying baseball all have kinetic energy.

Potential energy

Potential energy is energy stored in an object by virtue of its position or state. An example of this is gravitational potential energy, which is:

    PE = mass (m) × gravity (g) × height (h)

For example, a book on a shelf has potential energy because of its elevated position. If it falls, this potential energy is converted into kinetic energy.

Law of conservation of energy

The law of conservation of energy states that energy in an isolated system cannot be created or destroyed; it can only be converted from one form to another. This principle means that the total energy in a system remains constant over time.

Examples of energy transformations

Energy constantly changes from one form to another. Here are some examples:

Example 1: Falling object

When an object falls from a height, its gravitational potential energy is converted into kinetic energy. When it hits the ground, the energy may further be converted into sound or thermal energy.

Example 2: Battery-powered flashlight

In a flashlight, the chemical energy stored in the battery is converted into electrical energy and then into light energy.

Visual example

Potential energy Kinetic energy

This figure shows a falling ball, illustrating the transformation of potential energy into kinetic energy.

Power

Power is the rate at which work is done or energy is transferred over time. It tells us how quickly work can be done. The formula for power is:

    Power (P) = Work (W) / Time (t)

Power is measured in watts (W), where one watt is equal to one joule per second.

Practical examples of power

Example 1: Light bulb

A 60-watt light bulb consumes 60 joules of electrical energy every second to produce light and heat. Here, the power is 60 watts.

Example 2: Running

If you do 500 joules of work in 50 seconds, the power will be:

    Power = 500 J / 50 s = 10 W

Visual example

Power output

This diagram shows the power output, with the green block representing the object doing the work.

Conclusion

Work, energy, and power are interrelated fundamental concepts in physics. Understanding these concepts helps us understand the physical world and many of the processes that occur within it. By understanding how work is calculated, how energy can be transformed, and how power indicates the rate at which work is done, one gains a deeper understanding of the complex workings of the universe.


Grade 9 → 1.4


U
username
0%
completed in Grade 9

← Prev (1.3.8)
Satellites and their orbits
Next (1.4.1) →
Concept of work

Comments 



Work, Energy and Power

https://www.physicsflow.com/g9/1.4?pfal=en