Potential Energy

Bookmark added to your notes.
View Notes
×

What is Potential Energy?

We say that the energy that is stored in the human body is the potential energy. However, there is a great deal of relation between kinetic energy and potential energy.


Let’s say, you start playing with the cricket ball. Initially, this ball was at rest because of Newton’s first law of motion (the ball tends to stay at rest or in motion unless you subject it to an external force). Now, as you throw it far away, its potential energy transforms into kinetic energy.


Potential Energy Definition

In terms of Physics, we define potential energy as the energy protected/stored by an object due to its position relative to other objects, stresses/saves within itself, its electric charge, or other factors like energy. 

Below is the list of the common types of potential energy

  • The gravitational potential energy: The gravitational potential of an object depends on its mass and its distance from the center of mass of another object (that can be large or small).

  •  The elastic potential: The elastic potential energy of an extended spring, which converts to the kinetic energy on being stretched from its mean position.

  • The electric potential energy of an electric charge placed in an electric field.

Potential Energy

The term potential energy was introduced in the 19th-century  by the Scottish Engineer and Physicist named William Rankine, and this concept has a relationship with Greek philosopher Aristotle's concept of potentiality.


Potential Energy Examples

The below statement of potential energy examples illustrate the real-life applications of potential energy and here the relationship between the potential energy and kinetic energy is also explained very well:

  • Water at the top of the waterfall stores energy (which is the potential energy) and that energy helps rotate the turbine and convert its kinetic energy into electricity

  • A rubber band is an application of Newton’s first law of motion or the law of inertia. Now, as you apply force on it, it stretches and enlarges by length. Do you know why this happens? It is because the molecules inside the rubber band had initially stored energy and when you apply the force, all molecules set into motion because they gain kinetic energy set apart and the band stretches. 

  • You take a bow and an arrow, initially, they both have stored energy. Now, as you stretch the bow, and leave it, the arrow leaves the bow and reaches far away according to the magnitude of force applied by us. So, this stored energy or simply the potential energy gets transformed into kinetic energy by the force of our fingers.

  • You are lying on the bed and enjoying a weekend night of sound sleep, this time you are in a free energy state that means your energy is stored and as soon as someone wakes up, maybe alarm or your phone rings, you wake up, so this time your stored energy turns into a dynamism or the kinetic energy.

  • An AC generator is idle and as soon as the kinetic energy is offered to the generator, it starts rotating about the axis in either direction:  clockwise or counterclockwise. So, the energy stored in the generator is utilized to generate electricity during a power cut in the house.

Other Potential Energy Examples

  • A child sitting at the top of the swing has stored energy, which transforms into kinetic when he starts sliding down.

  • A car standing in the parking lot is having stored energy and when it starts, the accelerator sets it into motion. 

  • A truck standing at the tip of the mountain has potential energy unless it slides along with the mountain to reach the ground. Now, as the driver starts the truck, the truck utilizes all its stored potential energy to make drag down the ground. 

Potential Energy Units

The potential energy is denoted by U, V, or PE. The SI unit of the potential energy is Joule which is symbolized by an English letter ‘J’. 

The dimension of potential energy is [M¹L²T⁻²].


Relation Between Kinetic Energy and Potential Energy

In the last example, we discussed the scenario of a truck going up the tip of the mountain and then went down the mountain to reach the ground.

[Image will be Uploaded Soon]

So, initially, it had stored energy that is potential energy and then it started moving up the mountain, which is the kinetic energy, so the total energy utilized by it is given as:

KEi + PEi 

Now, as it is at the tip, and it again has a final stored or potential energy as it starts moving down the mountain, this stored energy transforms to kinetic energy. Now, the total energy used in the final case is as follows:

KEf + PEf

So, whatever total energy was used initially equals the energy used finally. So, our desired establishment of a relation between kinetic and potential energy is:

KE+ PEi     =    KEf + PEf

FAQ (Frequently Asked Questions)

Question 1: What Do You Mean by a Gravitational Potential Energy?

Answer: The gravitational potential energy of an object is the energy absorbed by an object to rise to a certain height by fighting against gravity. We shall formulate gravitational energy with the following example.

Let’s consider an object of mass as m placed at a height ‘h’ from the ground, as shown in the figure below:

[Image will be Uploaded Soon]

So, the work is done against gravity to reach height ‘h’ as:

W = F.s = mgh 

Question 2: What Do You Mean by Elastic Potential Energy?

Answer: The energy stored in objects that can be compressed/stretched viz: rubber bands, trampoline, and bungee cords is the elastic potential energy. 

If the object can stretch for a long period that means it has higher elastic potential energy. 

The following objects are specifically designed to store elastic potential energy:

  • A twisted rubber band that powers a toy plane/bungee cord

  • A stretchable bow

  • A bent diver’s board just before a diver dives in a river

  • Coil spring of a wind-up clock/generator/motor

Question 3: State the Formula for the Elastic Potential Energy of a Stretched Spring.

Answer: The formula for the potential energy is:

U = ½ kx² 

Here,

k = spring/force constant

x = The length by which a spring is stretched in meters

U = Elastic potential energy

Question 4: What Does Kinetic Energy Depend on?

Answer: Kinetic energy of an object depends on the mass and speed of an object.