Energy

physics

       Learn from yesterday, live for today, hope for tomorrow. The important thing is to not stop questioning.” ― Albert Einstein

 

 

 

 

Energy

 

                            Energy means invisible strength of doing work. Energy is a measure of how much work we can do. Energy needed to do certain work will always remain the same.

For example energy required to lift 500lits. of water to height of 10m. will always remain the same irrespective of doing it manually or by using engine. We can only do the work faster by using engine.

Common unit of energy is the kilowatt-hour (kWh). 1 KWh energy means, one kW of power will last one hour.

There are three Main types of Energy:- 

1) Kinetic Energy 

 
 

Kinetic Energy– is simply the energy in motion.

An energy possessed by a body because of its motion. If a body has energy, then it is capable of doing work. Energy has the capability of doing work on our body. Work = Force x distance        
    W = F*d Kinetic Energy
        = K.E. 
        = 1/2 mv^2 Joule (J) is the standard unit of Kinetic Energy

2) Potential Energy (Gravitational)

Potential Energy – the energy possessed by a body. It is also define as a stored energy. Either by virtue of its position or configuration.

Gravitational Potential Energy = mgh P.E. = mgh        Joule (J) is its standard unit. Elastic Potential Energy = 1/2kx^2 P.E. = 1/2kx^2   Newton meter (N/m) as its standard unit.1 N.m = 1 J




Mechanical Energy Theorem (Conservation of Mechanical Energy)
M.E = K.E + P.E





Conservation of Energy– The initial total of Mechanical Energy can be found and the Potential Energy decreases as Kinetic Energy (and speed) increases. In systems with non conservative forces, total M.E is changed. If friction is the non conservative force, then the total M.E is lost.
 

3) Chemical Energy 

Electrical, Heat, sound, solar, wind etc. are other examples of different forms of energy. Many times energy is invisible. It is visible by their effects.

Kerosene, diesel, food, wood contains energy in the form of chemical energy. When these things burn energy comes out in the form of heat energy. 

Stone falling from height (or anything in motion) contains energy. The object placed at highest place also contains hidden energy. This is called potential energy. 

An object in motion contains kinetic energy. 

Law of Energy Conservation

                                                 Energy can neither be created nor can be destroyed. Only one form of energy can be converted to other form of energy. Energy is immortal. It is not distortable. Energy Conversion

1. We eat food. Food contains chemical energy, in it after digestion this chemical energy is kept in the chemical form in our body and as and when required it gets burnt and gets converted into other forms of energy
2. When we fetch the water from the well, the energy in the form of chemicals in our body gets converted into potential energy of water. Water will contains energy equal to the amount of work done while lifting the water.
3. If we pour the water on the land, where the energy in it will go? If this water gets percolated in land then as it will go deep into the earth, potential energy in it will get converted into heat through friction. We never felt the heat since land is big and quantity of heat generated is comparatively smaller.
4. When we do cycling, chemical energy from food gets converted into kinetic energy. Once cycle catches the speed then we can move with same speed without peddling. At this time our body and cycle has kinetic energy in it. When we want to get down from the cycle, we reduce the speed by pressing the breaks. Kinetic energy gets converted into heat energy by friction and the ream of the cycle becomes hot.
5. Whenever we change the form of energy, some amount of energy gets wasted in the form of heat. Our objective is to convert maximum amount of energy in the desired form for use. This is called as efficiency.

      In diesel engine, when we burn diesel approximately 40% of energy gets converted into kinetic energy of water. When water is lifted to desire height, kinetic energy gets converted into potential energy. Remaining 60% of energy is wasted in the form of heat. This means the efficiency of diesel engine is 40%. In the past, relation between energy and work done was not clearly understood. Therefore, units of measurement of heat and work were different. Heat was measured in terms of calories and unit of work in terms of joule. These two units are still in use because it’s easier to calculate heat in calories and work in joule. 

We can convert calories into joule by using formula 1calorie = 4.2 joule.  Power is the rate of work done or rate of energy consumed. It tells us amount of joules used or required in one second. 

If one-joule energy is used in one second, then it is said that one-watt power is used.

Power (unit W watt) = J/S joule/second = Energy used (in joule) / time taken

 

Power

Power

 

                 Power is the rate of work done or rate of energy consumed. We can manually pedal a wheel of bicycle at 1 revolution per second. If we want to turn the same wheel with 10 revolutions per second, we need more power and will use engine. 

Power is the time rate of doing work (or expending energy).

P    =       W/t      

      =       Fd/t   

      =      mgh/t

The SI power unit is called watt (W) in honor of James Watt (1736-1819), a Scottish engineer who developed one of the first practical steam engines. A common unit of electrical power is the kilowatt (kW). Power tells you how fast work is being done or how fast energy is transferred.

The SI unit for power is watt. 
One watt is equal to 1 Newton-meter per second (Nm/s). 

If you were pushing on something with a force of 1 N, and it moved at a speed of 1 m/s, your power requirement would be 1 watt. 

British unit of power is horsepower.

The conversion is as follows: SI:

  Watts (W) 1000 W = 1 kW Kilowatt (kW) 
                      1kW = 1.341 hp Horsepower (hp)
                      1 hp = 0.746 kW

 

Work

 

Work is the application of a force over a distance. When we lift an object from the ground and put it on the shelf, we do work. The force is the weight of the object and distance is the height of the shelf. Similarly, when we push an object and moves it, we do work. The distance taken for calculating work has to be in the direction of force applied. 

Example: a weight of 50kg. is lifted to height of 5 meter. Calculate the work done. Work = force ´ distance through force is applied = (W kg ´ 9.8) ´ h (W = 50kg, h = 3m) = 50 ´ 9.8 ´ 3 = 1470 Nm
When we push an object and it moves through a distance L,
the work done is calculated as follows:
Work = force ´ distance through which force is applied 
W = F ´ L (unit of force is N, distance is in meter) 
W = F (N) ´ L (m) 
    = F ´ L (Nm) 

When we do work, we use energy. Work and Energy are closely related. Work is measured in the same unit of energy.

 

Torque

 

                    Torque is a force that tends to rotate or turn things. You generate a torque whenever, you apply a force to turn handle of diesel engine.

Torque = Force ´ Distance from the center. 

Unit of Torque = N ´ m = Nm. 

It is common experience, that a nut which is hard to move by hand can be easily rotated when a spanner of longer length is used. Increasing length of application of force from the center of shaft increases torque applied.

 

Mass and Weight

 Mass and Weight

                         Mass is defined as the measure of how much matter an object or body contains. It is measured in Gram (g). More the mass of object more is the gravitational force on the object. If we drop an object from a height, earth pulls it at the acceleration of 9.8m/s2

                            

                               Weight is the amount of force that earth exerts on us.

  

                                Acceleration is the rate of change of speed. This means speed of an object will increase by 9.8m every second. This means, if an object falls from a height to reach earth, after 10 second it would have achieve speed of 9.8 ×10 = 98 m/s. · Force causes acceleration, 

Sir Isaac Newton’s Second Law states that the acceleration (a) of an object is directly proportional to the force (F) applied, and inversely proportional to the object’s mass (m) Newton’s Second Law is usually summarized in equation form: 

 a = F/m, 

or F = ma 

Unit of force is derived as follows -

Unit of force F = m (Kg) × a (m/s2) 

                    = Kg m/s2 

                    = N 

To honor Newton’s achievement, the standard unit of force i.e kg m/s2 in the SI system is named as Newton (N). One Newton (N) of force is enough to accelerate 1 kilogram (kg) of mass at a rate of 1 meter per second square (m/s2). A kilogram is the amount of weight at which 1 N of force will accelerate at a rate of 1 m/s2. In practice, we measure weight, in terms of gms. or Kgs. But when weight is used as force, we must remember to measure it in terms of Newton.