Profile
Settings
Refer your friends
Sign out
Energy of a body can be defined as its capacity to do work. Energy can be of various types like thermal energy, mechanical energy, kinetic energy, potential energy, etc. Kinetic energy is the energy of the body by the virtue of its motion. It can exist in many forms – vibrational, rotational, or translational. At the molecular level, we talk mainly about translational forms of energy. Now, potential energy, on the other hand, is the energy of a body by the virtue of its position or shape. A sponge that is squished is said to possess potential energy because there is a change in its shape. A pendulum has potential energy when it goes to the extreme position by the virtue of its position. Gravitational potential energy has the same units as kinetic energy.
Potential Energy
The law of conservation of energy states that energy can neither be created nor be destroyed, but can only be converted from one form to another. Let’s take the example of a pendulum. The bob of the pendulum travels from its mean position to the extreme position and back to mean position. When it is at its mean position, it only has kinetic energy. Now as it moves up to the extreme position, the kinetic energy slowly transforms to potential energy as the bob of the pendulum gains height. Now, at the extreme position, i.e., when the bob is at its most height, there is no kinetic energy left and all of it has transformed to potential energy.
Potential energy can be of two types – gravitational potential energy and elastic potential energy. Gravitational potential energy is the energy in the body due to its height. It is called so because it exists because of the gravitational pull of the Earth on the object. Gravitational potential energy has the same units as kinetic energy.
It is the product of mass, acceleration due to gravity, and height at which the object is placed.
In mathematical terms, V = mgh (m is the mass, g is acceleration due to gravity, and h is the height)
Unit of m = kg
Unit of g (acceleration) =ms-2
Unit of h = m
Hence, the SI unit of gravitational potential energy = kgm2s-2 or Joules (J)
As can be seen, the gravitational potential energy has the same units as kinetic energy. Kinetic energy = 0.5mv2.
Elastic Potential Energy
It is possessed by a body by the virtue of its shape. Let’s take the example of a bow and an arrow. When the arrow is only placed on the bow and not stretched, it has no energy. As we start stretching it, it gains potential energy. Upon releasing the arrow, the potential energy gets converted to kinetic energy due to which it travels.
Now, the more an object is stretched, the more elastic potential energy it gains.
U= 0.5kx2 ; k is the spring force constant and x is the stretch length
Spring potential energy
It is the potential energy in a spring as it moves to and fro from its mean position. It can be derived by the formula of spring potential energy which is U= 0.5kx2.
Hooke’s law is used to arrive at the final formula. Hooke’s law states that the spring force is directly proportional to the displacement of the ends of the spring from their respective mean positions. Basically, the more the stretch, the more the displacement from mean position, and the higher the spring potential energy.
Conclusion
All energy contains the same units. Gravitational potential energy has the same units as kinetic energy. Elastic potential energy also has the same units. The SI unit is Joules. When we talk about energy in terms of thousands, kJ (kilojoules) is used. Potential energy is possessed in a body by the virtue of its position or shape. In springs, potential energy exists by the virtue of its position which is changed by stretching. For spring potential energy, we can assume one end of the spring to be fixed to the wall and we are stretching the other end. As we stretch, the spring force is proportional to the displacement from the mean position.
