WORK , POWER AND ENERGY
WORK: -
Definition: -
“The work done by a force acting on a body is the product of the force and the distance moved by its point of application in the direction of the force." (
Or
"Physical or mental effort or activity directed toward the production or accomplishment of something." (American Heritage Dictionaries)
Or
"The produce of a force by its corresponding displacement. " (McGraw Hill)
Or
"The product of the magnitude of the force and that of the displacement is called work" (
Mathematical Representation: -
Work = F.S
Where 'F' is the magnitude of force and 's' is the magnitude of displacement.
Explanation: - If however, 'F' makes an angle 0 (theta) with the direction of displacement 'S' then we take the component of force in the direction of displacement or the component of displacement in the direction of force, then
Work = F Cos 0 S
Work = F
Quantity: - It is a scalar quantity.
Unit: -
· In M.K.S system or in S.I units its unit is Joule
· In C.G.S system its unit is 'erg'
FACTORS AFFECTING ON MAGNITUDE OF WORK: -
Work done on a body by a force depends upon the following factors.
· Magnitude of force applied (work F)
· Distance traveled by the body under the influence of force (work F)
· Cosine of angle b/w applied force and the distance traveled by the body (work Cos 0 )
POSITIVE WORK: -
"If force and displacement vectors are along same direction then work will be positive
Cos 0 = +1
NEGATIVE WORK: -
"If force and the displacement vectors are in opposite directions. Then work will be negative.
Cos 180 = -1
MAXIMUM WORK: -
"If the angle '0' between applied force and distance covered the body is zero then work done on the body will be maximum."
MINIMUM WORK: -
"If the angle '0' between applied force and distance covered by the body is 90 degree the work done on the body will be minimum ( i.e. Zero)
JOULE
HISTORY: - A joule is the mechanical equivalent of heat meaning the number of units of work in which the unit of heat can perform.. Its value was found by James Prescott Joule in experiments that showed the mechanical energy Joule's equivalent, and represented by the symbol J. The term was first introduced by Dr. Mayer of
DEFINITION: -
"The SI unit of work and energy equal to the work done when the point of application of a force of one Newton moves, in the direction of the force, a distance of one metre. " (
Or
" The joule (symbol: J) is the SI unit of energy. It was named after James Prescott Joule for his work on the relationship between heat, electricity and mechanical work." (Wikipedia)
OR
"In SI units the work done by a force of one Newton in moving a body through a distance of one meter in the direction of force is one Newton meter (N-m), or one joule
1 JOULE = 1 N x 1m" (
RELATIONSHIP BETWEEN JOULE AND ERG: -
7
1 Joule = 10 erg.
OTHER UNITS: -
· One British thermal unit = 1055
· One electron volt = 1.6 x 10-19 J
· One Joule = 10 7 erg
ENERGY: -
INTRODUCTION: - In physics and other sciences, energy (from the Greek ενεργός, energos, "active, working") is a scalar physical quantity that is a property of objects and systems which is conserved by nature.
DEFINITION: -
"A measure of a system's ability to do work. " (
Or
" Energy is often defined as the capacity to do work." (Wikipedia)
Or
"The ability of a body to do work is called energy." (
UNIT: - It is measured in Joules.
KINETIC ENERGY: -
INTRODUCTION: -The adjective "kinetic" to the noun energy has its roots in the Greek word for "motion" ( kinesis). William Thomson, later Lord Kelvin, is given the credit for coining the term kinetic energy c. 1849.
DEFINITION: - "The kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its current velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. Negative work of the same magnitude would be required to return the body to a state of rest from that velocity." ( WIKIPEDIA)
OR
"The energy possessed by a body because of its motion, equal to one half the mass of the body times the square of its speed." (American Heritage Dictionaries)
EXAMPLE: -
For example, a cyclist will use chemical energy that was provided by food to accelerate a bicycle to a chosen speed. This speed can be maintained without further work, except to overcome air-resistance and friction. The energy has been converted into the energy of motion, known as kinetic energy but the process is not completely efficient and heat is also produced within the cyclist.
POTENTIAL ENERGY: -
DEFINITION: -
"Energy possessed by a body by virtue of its potential energy." (
Or
"Ability of a body to do work due to its position is called its potential energy." (
Or
"Potential energy is the energy of position, that is, the energy an object is considered to have due to its position in space." (wikipedia)
LAW OF CONSERVATION OF ENERGY: -
DEFINITION: -
"In a system which is not allowed to exchange energy with the surroundings, the energy can be changed into different forms but the total energy of the system remains constant. This is known as Law Of Conservation Of Energy." (
Or
"A law that states that in any system not involving nuclear reactions or velocities approaching the velocity of light, energy cannot be created or destroyed." (
Or
"The principle of conservation of energy states that energy cannot be created or destroyed, although it can be changed from one form to another." (McGraw Hill)
Or
"In an isolated system net amount of energy remains constant." (
Or
"Energy can neither be created nor be destroyed but it can change its form." (Dr. Saifuddin)
POWER
DEFINITION:-
"The rate at which work is done or energy is transferred." (
Or
"Work done in unit time is called power or rate of doing work is called power." (
Or
"The time rate of doing work." (McGraw Hill)
Formula: - power= Work
Time
Unit: - power= Joule = watt
Second
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