Chapter 2 work power and energy Selina concise (theory) Physics class 10th ICSE

Chapter 2 work power and energy Selina concise (theory) Physics class 10th ICSE
Definition & types of work
Definition of energy & energy as work done
Various units of work and energy
Definition of power & its units
Different types of energy
Potential and kinetic energy (With derivation)
Types of potential and kinetic energy
Conversion of one form of energy into another
Principle of conservation of energy
Work is said to be done only when the force applied on a body makes the body move.
Measurement of Work
The amount of work done by a force is equal to the product of the force and the displacement of the point of application of the force in the direction of force.
Work done = Force X displacement of the point of
application of force in the direction
of force
Expression of Work – When displacement is in the direction of force
Expression of Work – When force is in the direction of displacement
Work done = magnitude of force F X
magnitude of displacement S, X
cosine of the angle Ɵ between the direction of force F and displacement S (i.e., cos Ɵ).
Force – Vector Quantity
Displacement – Vector Quantity
Work – Scalar Quantity
Types of Work Done
Positive Work done
In free fall of a body of mass m under gravity through a height h.
A coolie/boy does work on the load when he raises it up against the force exerted by coolie and the displacement are in the upward direction.
Zero Work done
A man standing with a heavy load on his head
A man walks on a horizontal ground while carrying a load on his head. No work is done against gravity because the displacement of load is normal to the direction of force of gravity which is vertically downward.
Condition for the work done by a force to be Zero
When there is no displacement (i.e., S = 0),
When the displacement is normal to the direction of force (i.e., Ɵ = 90)
Negative Work done
When a body moves on a rough surface.
Graph Force v/s Displacement
Work done by the force of gravity
W = mgh
S.I Units of work done
1 joule = 1 Newton X 1 meter
When a force of 1 newton displaces a body of through a distance of 1m
1 erg = 1 dyne X 1 centi-meter
When a force of 1 dyne displaces a body of through a distance of 1cm
Relationship between
joule and erg
Power
The rate of doing of work.
Scalar quantity
Relationship between
Power, Force and velocity
If 1 joule of work is done in 1 second, the power spent is said to be 1 watt.
Relationship between
Watt and erg s-1
The energy of a body is its capacity to do work.
Calorie
Amount of heat energy required in raising the temperature of 1 g of water by 10 C.
Electron volt
1 eV is the energy gained by an electron when it is accelerated through a potential difference of 1 volt.
Mechanical Energy
Potential Energy
The energy possessed by a body at rest in its changed position or change in size and shape
kinetic energy
The Energy possessed by a body due to its state of motion
Gravitational potential energy – The amount of work done by the force of attraction of earth in bringing that body from infinity to that point.
Elastic potential energy – The energy stored in deformed state due to change in its size and shape
Expression for the Kinetic Energy
Kinetic energy possessed by a moving body is equal to the amount of work which the moving body can do before coming to rest.
Relationship between kinetic energy and Momentum
Work Energy Theorem
Increase in kinetic energy of a moving body is equal to the work done by a force acting in the direction of the moving body.
Forms of Kinetic Energy
Translational
Kinetic Energy
Rotational
Kinetic Energy
Vibrational
Kinetic Energy
Different forms of energy
Solar Energy- Energy radiated by sun
Heat Energy- Energy released on burning of coal, oil, wood or gas
Light Energy- Energy in which other objects are seen.
Chemical Energy- Energy possessed by the fossil fuels such as coal, petrol and natural gas.
Hydro Energy- Energy possessed by the fast moving water
Electrical Energy- The energy possessed by movement of free electrons
Nuclear Energy- Energy released due to loss in mass during the process of nuclear fission and fusion
Geo-thermal Energy- Energy released in nuclear disintegration in the interior of earth gets stored deep inside the earth.
Wind Energy- Energy possessed by the fast moving air.
Sound Energy- A vibrating body possesses the sound energy.
Magnetic Energy- Energy possessed by a magnet due to which it can attract iron filings.
Mechanical Energy- Energy possessed by a body due to its state of rest or of motion.
Conversion of Energy from one form to Another
Note – Whenever mechanical energy changes to other forms, it is always in the form of kinetic energy i.e., the stored potential energy first changes to kinetic energy and then kinetic energy changes to the other form.
Note – While transformation of energy from one form to the other desired form, the entire energy does not change into the desired form.