Difference Between Kinetic and Potential Energy

Difference Between Kinetic and Potential Energy - Applications

Introduction:


All of us are familiar with the word energy. When we lack energy, we say we are tired and unable to do anything productive. So, what is energy and what are its various forms?

Energy can be defined as the vitality and strength that are required for carrying out an activity. It is also explained as the power derived from the utilization of physical and chemical resources. 
 
In Science, however, energy is defined as the capacity to do work. This definition is still not very satisfactory to us, but it is difficult to define energy with great precision. Energy exists in many forms. Some of them are Potential Energy, Kinetic Energy, Chemical Energy, Nuclear Energy, Electrical Energy etc: Also, it is pertinent to note that there are other forms of energy like heat and work in the process of transfer from one body to another body. The unit of energy is Joules. 1 Joule = 1kg.m2/s2. It is a bit difficult to define energy in very precise terms because it is an abstract notion and not something tangible. Energy is generally carried by something, usually in the form of movement. When objects move or remain in a position, they have energy which has different names. 

Though energy exists in various forms as mentioned earlier, it is important to understand that energy remains conserved always. When a form of energy is converted from one form to another during any process, the overall quantity of energy remains the same; there is no loss or gain. This is what is called as conservation of energy. 

Our discussion here will focus on only two of the forms of energy – Potential Energy and Kinetic Energy.
Let us now go into each of these separately to understand them first.

POTENTIAL ENERGY:


An energy that is stored in an object and not moving, but which has the potential to move is called Potential Energy.

Potential Energy or PE as we can call is the energy possessed by an object because of its position relative to another body. The PE could also be the energy in a body due to its internal stress if any or the electrical charges in a body. One of the most common forms of PE is the gravitational potential energy. The amount of PE, in this case, depends on the mass of the body. This is the energy required to move a body against the force of gravitation of the earth. A spring when extended has energy in it waiting to come back to its original position. This also has enough potential energy. The term potential energy was first coined by a great physicist William Rankine in the 18th century. Potential energy is always determined based on the position of a body and not based on its trajectory of movement. Some of the important factors that impact PE are its mass, its height relative to another object, and strength of the gravitational field. Imagine a book or a ball of iron resting on a table at a height of 2 meters from the ground. If the same object were to be placed at a height of 10 meters from the ground, the object at the higher position will have a higher PE than the one at the lower height. It is also called as restoring energy because this in a way forces the object to come back to its original energy state.

When an object is raised from the ground, work is done against the gravitational force. Energy is spent in doing this work. When the object again falls to the ground, the object then gains energy from the gravitational energy. While the object falls and is in motion from its position of rest earlier, the PE gets converted to another form of energy. We will talk about the other form later.

Potential energy is measured by the formula PE = mgh,
where
m is the mass,
g is the acceleration due to gravity and
h is the height (or position).

Atoms or molecules are arranged form in different chemicals. The specific arrangement of the atoms and molecules to form a structure contributes to the chemical potential energy of a chemical substance. Also, when chemicals react, the energy will be transformed from one form to another. 

 For example: when a log of wood burns, the chemical energy is converted to heat.

Also attributable to electric charge, an object has electrostatic potential energy and electrodynamic potential energy.

There are particles inside the atomic nucleus. The particles inside also have energy which is the nuclear potential energy. 
 
KINETIC ENERGY:


The word Kinetic has its origin in the Greek language. In the Greek language, the word kinesis means "to move". This name was originally coined by William Thomson.

When an object is stationary it has Potential energy as we saw earlier. However, when the same object begins to move, then it releases Kinetic Energy.

While PE is the energy possessed by a body by virtue of its position, Kinetic Energy (KE) is the energy possessed by virtue of an object’s motion. In other words, the work needed to accelerate a body from rest to a required velocity is called kinetic energy of the object. This is true even for particles that are in motion. A person who throws a ball, a running train, or a falling drop of water are all examples of objects with kinetic energy. 
 
KE depends on two aspects of a body. One is mass of the object and other is the velocity with which it moves. Of the two, Velocity is more important and plays a key role in determining energy. There are different types of KE as we saw in PE. Some of them are Radiant, Thermal, Sound, Electrical and Mechanical. If an object is not moving, it has Zero KE. KE is given by the formula KE=1/2MV2 where M is the mass of the body and V is the velocity with which the object moves. 
 
Movement of an object can be Horizontal or Vertical for it to possess KE. 
 
Some of the important applications where see the significance of KE is as follows:

  • 1. In automobiles, the fuel is burnt, and the heat energy is converted to a motion which is again Kinetic energy in action.

  • 2. In hydroelectric plants, when water is stored it has potential energy, then it flows down, and the PE gets converted to KE and the KE is converted to electrical energy.

  • 3. In Windmills, the wind rotates the blades and this rotational kinetic energy is converted to electrical energy.

  • Now let us look at some of the differences that are significant, between PE and KE

    Kinetic Energy (KE)
    Potential Energy (PE)
    KE is the energy possessed by an object by virtue of it being in motion.PE is the energy possessed by an object by virtue of its position.
    It can be transferred from one object to another and this happens during collisions. Potential Energy, on the other hand, cannot be transferred from one object to another.
    When Kinetic Energy is measured, the measurement is done at the point where the object is at the time of measurement. Ex: If a ball is traveling at a speed of 50m/s upwards and if we want to measure the Kinetic energy at a height of 3 meters above the ground, the measurement is done at that point and not with reference to another point.When Potential energy is measured, the measurement is done by measuring the position from the reference position. If a ball is at a height of 10m above the ground and at rest, the potential energy is measured from the ground as a reference
    The formula to measure Kinetic energy involves velocity and is measured as mentioned earlier.Potential Energy is based on mass, gravity, and height.
    Environment impacts Kinetic Energy and is relative to the environment Potential Energy, on the other hand, is not influenced by environment.
    Kinetic Energy is already moving and is not at rest.Potential Energy is purely based on the position of the object and also the condition of the object.


    Now with this information, you should try to identify which of the following are Potential Energy examples and which the examples are for Kinetic Energy:

    Two magnets kept apart, a running train, Snow on top of a mountain, an avalanche, a ball in the hand of a player, a cricket ball traveling at 80km/hr.

    Answer for the above in the same order as the questions: PE, KE, PE, KE, PE, KE.

    Wherever there is no motion involved the energy that we refer to is Potential Energy. Wherever there is motion involved the energy referred to be Kinetic Energy.

    To conclude, you just have to remember that Potential Energy is due to Position, and Kinetic energy is due to motion. Also, Potential energy can be converted to Kinetic and the reverse is also true. However, in any such process of conversion, energy is conserved. There is no loss or gain of energy. This is the law of conservation of energy.