Potential energy is the energy stored within an object because of its position relative to others. Internal stresses, electric charge, and other factors can also result in potential energy.
In this article, we are going to discuss this concept and its types. We will also look at the examples of potential energy that are present in everyday life.
What is Potential Energy?
Potential energy refers to the stored energy held by an object due to its position relative to others, electric charge, internal stresses, or other factors. The standard unit of measuring it is the joule (J).
The concept was first developed by the Scottish engineer and physicist William Rankine in the 19th century. However, the ancient Greek philosopher Aristotle also had a related concept known as potentiality.
Potential energy is the property of a system and is based on the parts of the system. For example, if a ball is raised, then the system consists of the ball and the Earth. Potential energy arises when parts of the system exert force on each other.
Here, the force is gravity, and it depends on the distance between the two parts (ball and Earth). More work is required to separate the two (raise the ball higher), and this gets stored as additional energy in the system.
The potential energy in this case is calculated by:
PE = m×g×h = mgh
Here “m” refers to the mass of the object, “g” is the acceleration due to gravity, and “h” refers to the height to which the object is raised.
Types of Potential Energy
There are several types of potential energy, such as:
Gravitational Potential Energy
Gravitational potential energy is the energy stored in an object that is raised above the earth. It needs to work against gravity and this is what gets stored as potential energy.
The gravitational energy does not depend on the path traveled by the object but only on its displacement, that is, the distance between its initial and final position. So, if the initial position of the ball is on the ground and the final position is 20 meters above the Earth, then irrespective of how the ball was raised, its potential energy will remain the same.
Suppose a 1kg ball is lifted 2 meters above the ground, then, its potential energy would be
PE = m×g×h = 1kg×2m x 9.8m/s2
= 19.62 joules
Elastic Potential Energy
Elastic potential energy is the energy stored in an object that is stretched, compressed, or bent. It requires force to deform an object and this gets stored in it as potential energy; this can be released to do work when the object returns to its original state.
The amount of elastic potential depends on the material properties of the object and the amount of deformation it goes. So, a stiffer spring requires more force to compress or stretch it, and therefore stores more elastic potential energy than a flexible spring of the same size.
Elastic potential energy is calculated by the formula:
PE = 0.5kx2
Here, k is the spring constant (in newtons per meter), which represents the stiffness of the spring. X refers to the displacement of the spring from its equilibrium position (in meters).
For example, if a spring with a spring constant of 20 N/m is compressed by 0.1 meters from its equilibrium position, then its elastic potential energy would be:
PE = 0.5 x 20 N/m x (0.1 m)2 = 0.1 joules
Besides gravitational and elastic potential energy, there are other types of potential energy as well, such as chemical potential energy, electric potential energy, and nuclear potential energy.
Examples of Potential Energy in Daily Life
1. Rubber band: An object gains elastic potential energy when it is deformed. When we stretch a rubber band, we apply a force against its resisting strength and this gets stored in the form of elastic potential energy. When we release the force, the potential energy gets converted into kinetic energy, as the band snaps back to its original state.
2. Water bottle sitting on a table: A water bottle sitting on a table has gravitational potential energy due to its position relative to the Earth. If the bottle is lifted above the table, it gains more gravitational potential energy as the distance between it and the Earth increases (upon which potential energy depends). If the bottle is released, the potential energy turns into kinetic energy as the bottle falls.
3. Pendulum: A pendulum (like a clock) is a structure in which a weight is suspended from a pivot, allowing it to swing freely. When we take the pendulum to one end, we apply a force against gravity and this gets stored as potential energy. Upon release, this potential energy gets converted into kinetic energy as the pendulum swings to the other end. At the other end, the kinetic energy turns into potential energy and the process repeats.
4. Hammer held above a nail: A hammer held above a nail has gravitational potential energy due to its relative position. One needs force to lift the hammer above ground (against gravity) and this gets stored in it as potential energy. When we bring the hammer down, the potential energy turns into kinetic energy and the hammer drives the nail to the surface.
5. Balloon: A balloon is made up of elastic, so it has elastic potential energy. As we know, such energy requires a force that can deform an object. So, when we fill the balloon with air, it gets stretched and stores this force as potential energy. When the balloon is released, the air inside escapes, and the elastic energy turns into kinetic energy.
6. Bow & Arrow: When an archer stretches the bowstring, the force needed to deform the bowstring is stored as potential energy in the system. When the string is released, this potential energy turns into kinetic energy, which is transferred to the arrow that moves forward. The more the bowstring is stretched (without breaking), the greater the potential energy, and the further the arrow will travel.
7. Rock on a cliff: A rock lying on a cliff will have gravitational potential energy because of its position. If we push it, then this will convert into kinetic energy, and the rock will go tumbling down.
8. Food: Food has stored chemical potential energy. This is the energy stored in the chemical bonds of the substance. When we eat it, our body is able to break down the chemical bonds and take out necessary elements like vitamins, minerals, proteins, etc. We can then use this energy to do various activities.
9. Water Tank/Dam: Domestic water tanks are usually placed on top of the houses, and because of the height, the water acquires potential energy. When the tap is opened, this water comes with pressure for our use. Similarly, the water stored in dams has tremendous potential energy. When released, it turns into kinetic energy and this can be used to generate electricity.
10. Battery: A battery has electrical potential energy because of its chemicals. When the battery is connected to a circuit, the stored energy is transformed into electrical energy. This is then used to power devices.
11. Firecrackers: Firecrackers have chemical potential energy in their explosive chemical compounds. When they are ignited, this chemical potential energy is released in the form of heat, light, and sound.
12. Rollercoaster: When a rollercoaster wagon is at the top of the structure, it has gravitational potential energy due to its position. The more people are there on the ride, the higher the weight, and therefore the greater the potential energy.
13. Tree Branches: A tree branch has elastic potential energy stored in its fibers. Force is required to bend it, which is stored and released when the branch returns to its original shape. Branches are also at a height, so they also have gravitational potential energy.
14. Spring: A spring has elastic potential energy. When we stretch or compress it, we apply force to it, and this gets stored as potential energy. Upon release, the potential energy transforms into kinetic energy as the spring snaps back to its original state.
15. Wood: Wood has chemical potential energy stored in its atoms. When we burn it, the chemical bonds between its atom break. Their breaking releases energy in the form of light, heat, etc.
Potential Energy & Kinetic Energy
Potential energy and kinetic energy can be transformed into each other. When an object gains potential energy, it has the potential to do work (move an object or lift a weight). When this potential energy is released, it is transformed into kinetic energy—the energy of motion.
The law of conservation of energy states that energy cannot be created or destroyed, only transformed from one form to another. So, potential energy can be converted into kinetic energy and vice versa.
For example, when a ball is raised above the ground, it gains potential energy due to its position (being against gravity). When the ball is released, the potential energy is transformed into kinetic energy as the ball falls to the ground.
The law of conservation of energy implies that the total energy in a system is constant. So, when an object gains/loses potential energy, it also gains/loses an equal amount of kinetic energy, thereby maintaining the balance of the system.
In this article, we have discussed the concept of potential energy and looked at its examples. Potential energy is energy stored in an object due to its position relative to others. It can also be due to the object’s internal stress, chemical energy, electric charge, etc. Potential energy can be turned into kinetic energy and vice versa.