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:
- ${\rm{W}} = {\rm{F}} \cdot {\rm{s~}}$
where
${\rm{W}} =$ work done in the direction of the applied force.
${\rm{F}} = $ force
${\rm{s}} = $ displacement - ${\rm{W}} = {\rm{F}} \cdot {\rm{s}} \cdot {\rm{cos}}\theta ~$
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 - ${\rm{W}} = m \cdot g \cdot h$
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:
- The magnitude of the effective applied force.
Work done is directly proportional to the magnitude of the effective applied force. - 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:
- Mechanical Energy:
The sum total of kinetic energy and potential energy of the body is known as mechanical energy. - Thermal energy
The energy possessed by a body due to its temperature is known as heat or thermal energy. - Chemical energy
The energy released in chemical reaction is known as chemical energy. - Sound Energy
The energy of a vibrating body producing sound is known as sound energy. - Electrical energy
The energy of the moving electrons in a conductor connected with a battery is known as electrical energy. - 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. - Solar energy
The energy radiated by the sun is known as solar energy.