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Class 9, Science, Chapter-10, Lecture-1, Work (Notes)

WORK:

Work is said to be done by a force on an object if the force applied causes a displacement in the object, and is equal to the magnitude of the effective force in the direction of displacement multiplied by the magnitude of the displacement.

Mathematically:

  1. ${\rm{W}} = {\rm{F}} \cdot {\rm{s~}}$
    where
    ${\rm{W}} =$ work done in the direction of the applied force.
    ${\rm{F}} = $ force 
    ${\rm{s}} = $ displacement 
  2. ${\rm{W}} = {\rm{F}} \cdot {\rm{s}} \cdot {\rm{cos}}\theta ~$ 
    where
    ${\rm{W}} =$ work done at an angle $\theta $ with the direction of the applied force ${\rm{F}} $
    ${\rm{F}} =$ force applied at an angle $\theta $ with the direction of displacement ${\rm{s}} $
    ${\rm{s}} =$ displacement
    $\theta =$ angle between the direction of applied force and the the direction of the displacement
  3. ${\rm{W}} = m \cdot g \cdot h$ 
    where
    $g =$ acceleration due to gravity
    $h =$ height 
  • Work is a SCALAR quantity.
  • SI unit of work is joule ( J )

Factors on which work done depends:

  1. The magnitude of the effective applied force.
    Work done is directly proportional to the magnitude of the effective applied force.
  2. The displacement of the body in the direction of applied force.
    Work done is directly proportional to the magnitude of the displacement.

Definition of one joule:

The work done by a force of one newton in displacing a body through one metre in the direction of the force is termed as one joule of work.

ENERGY:

The capacity to do work is termed as energy.

Types of energy:

  1. Mechanical Energy:
    The sum total of kinetic energy and potential energy of the body is known as mechanical energy.
  2. Thermal energy
    The energy possessed by a body due to its temperature is known as heat or thermal energy.
  3. Chemical energy
    The energy released in chemical reaction is known as chemical energy.
  4. Sound Energy
    The energy of a vibrating body producing sound is known as sound energy.
  5. Electrical energy
    The energy of the moving electrons in a conductor connected with a battery is known as electrical energy.
  6. Nuclear energy
    The energy released when two nuclei of light elements combine with each other to form a heavy nucleus or when a heavy nucleus breaks into two light nuclei is known as nuclear energy.
  7. Solar energy
    The energy radiated by the sun is known as solar energy.