Potential and Kinetic Energy

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What is Energy?

Energy is the capacity to do work in physics. It exists in potential, kinetic, thermal, electrical, chemical, nuclear, or other forms.


Potential Energy

Potential energy definition states that “It is the energy stored that depends on the relative location of the different parts of the system”. In systems with parts that exert forces on each other of a magnitude depending on the configuration or relative position of the parts, potential energy arises.


When compressed or extended, spring has more potential energy. A steel ball after dropping to Earth has less potential energy compared to when lifted above the ground. Potential energy is capable of doing more work in an elevated role. Potential energy is a system property and not of an individual body or particle; for example, the system consisting of Earth and the raised ball has more potential energy as the two are separated further.


The potential energy of an object depends only on its original and final configurations. It is independent of the direction travelled by the objects. If the initial position of the ball is ground level and the final position is 10 m above the ground, in this case of the steel ball and the Earth, the potential energy is the same, regardless of how or by what route the ball was lifted. The value of potential energy is arbitrary and is proportional to the reference point selection. In the above example, if the initial location was the bottom of a 10 m deep pit, the device would have twice as much potential energy.


Different Types of Potential Energy

  • Electrical potential energy is the energy stored between the plates of a charged capacitor.

  • Chemical energy, the ability of a substance to work or to produce heat from a change in structure, may be considered as potential energy arising from the reciprocal forces between its molecules and atoms.

  • Nuclear energy is a form of potential energy as well.

Gravitational Potential Energy

The potential energy that a massive object has another massive object due to gravity is Gravitational Potential energy. When the objects fall towards each other, it is the Potential energy associated with the gravitational field that is released.

By multiplying the weight of an object by its distance above the reference point, Gravitational Potential energy near the Earth's surface can be measured.

Inbound structures, such as atoms, where electrons are retained by the electrical force of attraction to nuclei, the zero references for Potential energy is such that the distance from the nucleus is not measurable by the electrical force. Bound electrons have negative Potential energy in this case, and those so far away have zero Potential energy.


Potential Energy Formula

The Gravitational Potential energy formula relies on the force that acts on the two objects. The formula for the Gravitational Potential energy is,

P.E. = m*g*h 

Where m is the mass in kilograms,

g is the acceleration due to gravity(9.8 m/s2 at the earth's surface) and 

h is the height in meters.

The SI unit of measurement of Potential energy is kg. m2/s2 or Joule(J).


Some examples of Potential energy includes:

  • Compressed or extended spring.

  • A ball raised to some height.

  • Stored water in the Dam.

  • A car parked on the hilltop.

  • An arrow about to be shot.

Kinetic Energy

Kinetic energy is the form of energy in which the object or a particle is said to be in motion. If the work that transfers energy is done on an object by applying a net force, the object speeds up and thus gains kinetic energy.


Kinetic energy is a property of a moving object or particle which depends not only on its movement but also on its mass. Translation, rotation around an axis, vibration, or some combination of motions can be the form of Kinetic energy.


Kinetic Energy Formula

Kinetic energy is directly proportional to the object's mass and its velocity square, which is  

K.E. = 12*m*v2

Where m is the mass in kilograms,

v is the velocity in m/s.

The SI unit of measurement of Kinetic energy is the same as Potential energy which is kg. m2/s2 or Joule(J).


The Relation Between Potential Energy and Kinetic Energy

Kinetic energy is nothing but a form of converted potential energy. Potential energy can be transformed into the energy of motion such as kinetic energy and in turn into other forms, such as electric energy. Thus, through turbines that transform electric generators, water behind a dam flows to lower levels, generating electric energy plus some unusable heat energy resulting from turbulence and friction.

Potential energy and Kinetic energy are a form of mechanical energy so that the total energy in gravitational systems could be calculated as a constant.


Some examples of Kinetic energy includes:

  • Windmill.

  • Moving vehicle.

  • Running and Walking.

  • Bullet fired from a gun.

  • An arrow shot from a bow.

  • Cycling.

Solved Numerical on Potential and Kinetic Energy

1. In a running race competition, a student who is weighing 40 Kg is running at 4m/s. Calculate the Kinetic energy of the student.

Ans: It is given that the weight/mass of the student, m = 40 Kg.

The velocity of a student, v = 4m/s.

Kinetic energy is given by the formula, K.E.=12*m*v2

Substituting the values we get, K.E.= 1/2 * 40 * 4*4 = 320 kg. m2/s2.

Therefore the Kinetic energy of the student is 320 kg. m2/s2.


2. A water tank of mass 50 Kg is stored at a height of 10m. Calculate the potential energy of the tank. Consider the value of acceleration due to gravity(g) = 10 m/s2.

Ans: Given the mass of the tank, m = 50 Kg.

Height = 10m and g = 10 m/s2.

Potential energy formula is given as P.E. = m*g*h.

Substituting the values we get P.E. = 50*10*10= 5000 kg. m2/s2.

Therefore the Potential energy of the tank is 5000 kg. m2/s2.

FAQs (Frequently Asked Questions)

1. What is Energy?

Ans: Energy in physics is the quantitative property that must be transferred to an object to operate on the object, or to heat it.

2. What is Potential Energy?

Ans: In physics, the energy retained by an object is Potential energy regardless of its location relative to other objects, stresses within itself, its electrical charge, or other variables.

3. What is Kinetic Energy?

Ans: In physics, an object's Kinetic energy is the energy it possesses due to its motion. It is defined as the work required to accelerate from rest to the specified velocity of a body of a given mass. Having accumulated this energy through its acceleration, until its speed increases, the body retains this Kinetic energy.

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