Work And Energy Class 9 CBSE Notes - Chapter 11
Introduction to Work and Energy
The class 9 Chapter 11 Work and Energy discusses the concept of work, energy and power in detail. In
day-to-day life, we consider any useful physical or mental labour as work. But work is defined differently in
Science. Work done by a force acting on an object is equal to the magnitude of the force multiplied by the
distance moved in the direction of the force. Work has only magnitude and no direction. Similarly, we often
use the term energy in our daily life, but in science, energy is defined differently. In physics, energy is the
quantitative property that is transferred to a body or to a physical system, recognizable in the performance
of work and in the form of heat and light.
Work
Work done on an object is defined as the product of the magnitude of the force acting on the body and the
displacement in the direction of the force. W = F.s. The SI unit of force is Newton.
If a force acting on a body causes no displacement, the work done is 0. For example, pushing a wall.
The force component F cos θ gives the component of force along the direction that the body is displaced.
Cos θ is the angle between the force vector and displacement vector.
To know more about Work, visit here.
Energy
Energy is defined as the ability to do work. Its unit is the same as that of work. Energy is a scalar quantity.
SI unit of energy or work = Joule (Nm) or Kgm2s−2.
, Forms of Energy
Energy has different forms: Light, heat, chemical, electrical or mechanical.
Mechanical energy is the sum of:
(i) Kinetic energy (K.E)
(ii) Potential energy (P.E)
To know more about Energy and its type, visit here.
Kinetic Energy
Objects in motion possess energy and can do work. This energy is called Kinetic Energy.
Also,
From the second equation of motion, we know that
Rearranging the equation, we get
Substituting equation for work done by a moving body,
Taking initial velocity as zero, we get
Introduction to Work and Energy
The class 9 Chapter 11 Work and Energy discusses the concept of work, energy and power in detail. In
day-to-day life, we consider any useful physical or mental labour as work. But work is defined differently in
Science. Work done by a force acting on an object is equal to the magnitude of the force multiplied by the
distance moved in the direction of the force. Work has only magnitude and no direction. Similarly, we often
use the term energy in our daily life, but in science, energy is defined differently. In physics, energy is the
quantitative property that is transferred to a body or to a physical system, recognizable in the performance
of work and in the form of heat and light.
Work
Work done on an object is defined as the product of the magnitude of the force acting on the body and the
displacement in the direction of the force. W = F.s. The SI unit of force is Newton.
If a force acting on a body causes no displacement, the work done is 0. For example, pushing a wall.
The force component F cos θ gives the component of force along the direction that the body is displaced.
Cos θ is the angle between the force vector and displacement vector.
To know more about Work, visit here.
Energy
Energy is defined as the ability to do work. Its unit is the same as that of work. Energy is a scalar quantity.
SI unit of energy or work = Joule (Nm) or Kgm2s−2.
, Forms of Energy
Energy has different forms: Light, heat, chemical, electrical or mechanical.
Mechanical energy is the sum of:
(i) Kinetic energy (K.E)
(ii) Potential energy (P.E)
To know more about Energy and its type, visit here.
Kinetic Energy
Objects in motion possess energy and can do work. This energy is called Kinetic Energy.
Also,
From the second equation of motion, we know that
Rearranging the equation, we get
Substituting equation for work done by a moving body,
Taking initial velocity as zero, we get
