1. Work, Energy, and Power:
    • Work is a key concept in physics to understand natural phenomena.
    • Energy and power are closely linked to work.
    • Living beings and machines both require energy to perform activities.

Work (Scientific Definition)

Key Points:

  • In day-to-day life, work means physical or mental effort.
  • In science, work requires two conditions:
    1. A force must act on an object.
    2. The object must be displaced in the direction of the force.

Examples of Work in Science:

  1. Pushing a pebble on a surface causing it to move – work is done.
  2. Lifting a book upward involves force and displacement – work is done.
  3. Standing still holding a weight – no work is done (no displacement).
  4. Pushing a rock that doesn’t move – no work is done (no displacement).

Work Done Formula

  • Work done (W): W=F⋅s, where:
    • F= Force applied (N)
    • s= Displacement in the force’s direction (m)

Units of Work:

  • SI unit: Newton-meter (N·m) or Joule (J).
    • 1 J: Work done when a force of 1 N displaces an object by 1 m.

Positive and Negative Work

  • Positive Work:
    • Force and displacement are in the same direction (e.g., pulling a trolley forward).
  • Negative Work:
    • Force opposes displacement (e.g., friction slowing a moving object).

Energy

Definition:

  • Energy is the ability to do work.
  • Any object capable of doing work possesses energy.

Measurement of Energy:

  • Same unit as work: Joule (J).
  • 1 J: Energy required to do 1 J of work.
  • Larger unit: 1 kJ=1000 .

Forms of Energy

  1. Mechanical Energy:
    • Potential Energy + Kinetic Energy.
  2. Heat Energy.
  3. Chemical Energy.
  4. Electrical Energy.
  5. Light Energy.

Examples:

  • A moving car possesses kinetic energy.
  • A stretched spring stores potential energy.

Kinetic Energy (Ek​)

Definition:

  • Energy possessed by an object due to its motion.

Formula:

  • Ek=1/2 mv2, where:
    • m= Mass of object (kg).
    • v= Velocity of object (m/s).

Key Insights:

  • Ek​ increases with the square of velocity (double velocity → four times Ek​).
  • Faster moving objects can do more work.

Practical Examples:

  • A moving bullet pierces a target due to Ek​​.
  • Flowing water rotates turbines, converting Ek​​ into electrical energy.

Work-Energy Theorem

  • The work done on an object is equal to the change in its kinetic energy.

Proof Outline:

  1. From Newton’s 2nd Law: F=ma.
  2. Using equations of motion: v2−u2=2as.
  3. Substituting in work formula:
    W=F⋅s= ½ ​m(v2−u2).
    • If u=0: W=1/2 mv2, which equals the object’s Ek..

Competitive Question Insights

  1. Identify when work is done:
    • Check for both force and displacement in the force’s direction.
  2. Conceptual Difference:
    • No displacement → No work (e.g., holding a weight).
  3. Energy Conversions:
    • Analyze scenarios of energy transformation (e.g., potential → kinetic).

Real-Life Applications of Work and Energy

  • Machines like engines require fuel (chemical energy) to perform work.
  • Renewable energy sources like wind and water utilize kinetic energy.
  • Everyday activities like cycling involve energy transformations.

Potential Energy of an Object at a Height

Concept:

  • When an object is raised to a height, work is done against gravity, increasing its energy.
  • This energy is called gravitational potential energy.

Gravitational Potential Energy (GPE):

  • Defined as the work done to raise an object from the ground to a certain height against gravity.
  • Formula: Potential Energy (Ep)=mgh, where:
    • m= mass of the object (kg)
    • g= acceleration due to gravity (9.8 m/s2)
    • h= height above the ground (m)

Key Points to Remember:

  1. Work Done: The minimum force needed to lift an object is equal to its weight (mg).
    • W=Force×Displacement=mgh
  2. The object gains energy equal to the work done on it (mgh), which is stored as potential energy.

Path Independence:

  • The work done by gravity depends only on the vertical height difference, not on the path taken (e.g., straight or curved path).

Law of Conservation of Energy:

  • Energy Transformation: Energy can change forms (e.g., potential to kinetic), but the total energy in a system remains constant.
  • Free-Fall Example:
    • At the top: Potential Energy = mgh, Kinetic Energy = 0
    • Midway: Ep decreases, KE=1/2 mv2 increases.
    • At the bottom: Ep=0, KE is maximum.
    • Total Energy (Ep+KE) remains constant.

Power – Rate of Doing Work:

  • Formula:P=Wt, ​where:
    • P= Power (watts, W)
    • W= Work done (Joules, J)
    • t= Time taken (seconds, s)
  • Unit Conversion:
    1 kilowatt (kW) = 1000 watts (W)

Important Concepts:

  1. Average Power:
    • Average Power=Total Work or Energy/Total Time​
  2. Mechanical Energy:
    • Total mechanical energy = Potential Energy + Kinetic Energy.
  3. Energy Forms:
    • Energy can exist as kinetic energy, potential energy, heat, chemical energy, etc.
  4. 1 Watt of Power:
    • Defined as 1 joule per second (1 J/s).

Practical Understanding:

  • Green plants convert sunlight into chemical energy (photosynthesis).
  • Fuels like coal and petroleum store chemical energy, formed over millions of years.
  • Natural phenomena like the water cycle involve energy conversions (solar to kinetic).

Application in Competitive Questions:

  • Use the GPE formula for direct calculations.
  • Understand the law of energy conservation to solve free-fall or motion-related problems.
  • Power calculations often appear in real-world scenarios like electric appliances and work efficiency problems.

THESE ALL ARE THE NOTES OF CHAPTER 10 SCIENCE. AND AFTER SOME TIME YOU GET IMPORTANT QUESTIONS HERE. *#THANKS FOR VISITING, VISIT AGAIN#* 😊