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Energy
KINDS OF ENERGY
In actual practice there are many kinds of energy, such as mechanical energy; heat energy; light energy; sound energy, electrical energy; nuclear energy; chemical energy, etc. Let us discuss about mechanical energy. -
Energy
¶¶ Mechanical energy (M.E)
The sum of kinetic energy (K.E) and potential energy (P.E) of a body is known as mechanical energy.
\(\therefore\) M.E = K.E + P.E
¶¶ Kinetic energy:-
The kinetic energy of an object is a measure of the work an object can do by the virtue of its motion.Therefore kinetic energy is defined as ”the energy possessed by a body by virtue of its motion”.
Let
m = mass of the body, u = Initial velocity of the body (= 0)
F = Force acting on the body, a = Acceleration of the body
s = Distance travelled by the body, v = Final velocity of the body
From
\( \begin{gathered} v^2 = u^2 + 2as \hfill \\ \Rightarrow v^2 = 0 + 2as \hfill \\ \therefore s = \frac{{v^2 }} {{2a}} \hfill \\ \end{gathered} \)
Since the displacement of the body is in the direction of the applied force, then work done by the force is
\( \begin{gathered} W = F \times s = ma \times \frac{{v^2 }} {{2a}} \hfill \\ \Rightarrow W = \frac{1} {2}mv^2 \hfill \\ \end{gathered} \)
This work done appears as the kinetic energy of the body \( KE = W = \frac{1} {2}mv^2 \)
Since mass and square of velocity are always positive K.E. never be negative.
Examples:
1.A vehicle in motion.
2.Water flowing along a river.
3.A bullet fired from a gun.
4.A running athlet have kinetic energy. -
Energy
¶ ¶ Potential Energy:- The energy possessed by a body by virtue of its state or position is known as potential energy.
Expression for gravitational potential energy :
Consider a body of mass 'm' is on the ground. It is lifted verticaly upwards through a height 'h'. Considering the height to be very small compared to the radius of the earth (R)i.e., h<<R, we can neglect the variation of g. The gravitational force 'mg' on the body can be taken to be constant. The work done by the external agency against gravitational force is
W = Fs = mgh. (\(\therefore\)F=mg;s=h)
This work gets stored as potential energy of the body. Potential energy of the body \(\boxed{U=mgh.}\)
The above expression actually represents the increase in the stored energy from the
reference position (earth surface) to the final position at a height 'h'.
Examples:
1.Water on hill top and stretched or compressed spring possess potential energy.
2.stone at a certain height.
3.The spring wound in a watch possesses potential energy
4.An arrow in a bowl possesses potential energy. -
Energy
¶¶ Gravitational potential energy :-
The Potential energy due to height above the earth’s surface is called gravitational potential energy.
In general, if the potential energy at the ground is taken as zero, the potential energy of an object at a height h above the ground is given by
U = mgh
The energy results from the force of attraction mg between the earth and the object.From newton’s third law, both earth and the object attract each other. Hence, strictly speaking energy ‘mgh’ is not the potential energy of the object alone it is the potential energy of object-earth system.
¶¶ Heat Energy:- Heat is the energy that is transferred between a system and its environment because of a temperature difference that exists between them.
Heat is an Internal energy that consists of the kinetic and potential energies associated with the random motion of the atoms, molecules and other micro scopic bodies within object. -
Energy
¶¶ Sound Energy:-
Sound is a form of energy, that is produced by a body when it is in the state of vibration. It propagates in the form of Longitudinal waves through Elastic media and causes sensation of hearing.
¶¶ Light Energy:-
*Light is a form of energy, which causes sensation of vision.
*Light travels from one place to another place in the form of Electromagnetic waves.
*E.M wave can transport energy and deliver it to a body on which it falls.
¶¶ Elastic potential energy :-
When a spring is streched or compressed from its natural length, its get extra energy. It can return to its natural length by performing some work.
The extra energy stored in a streched or compressed spring is called elastic potential energy.
A streched rubber band also has potential energy, where as rubber band at its natural length lying on a table has no elastic potential energy. -
Energy
§§ Other forms of energy :-
Besides mechanical energy, energy can exist in several other forms.
Charged particles and electric currents can produce electrical energy and magnetic energy.Electric batteries,cooking gas,petrol etc., have chemical energy stored in them.Even matter itself is a concentrated form of energy and can be converted into other forms of energy such as kinetic energy and heat energy.
¶¶ Electrical energy :
Energy is associated with electric current is called electrical energy
The flow of electrical current causes bulbs to glow, fans to rotate and bells to ring.