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In very simple terms, mechanical energy is the energy owned by an object in a closed system due to its position or motion. The position contributes to potential energy and the motion is the kinetic energy of the object. Predominantly, the addition of the potential and kinetic energy gives the total mechanical energy in an object in reference.
Potential Energy
The positioning of the object gives it its potential energy. Assume a book on the floor. It has very low potential energy in this state. Now you pick it up and place it on the table at a certain height from the floor. What you just did (in physics jargon) is you applied force against the gravitational pull on the book and placed it on the table. Your work on the book gets stored as potential energy in the book. The more height you give to it, the more work you have to do, and the more potential energy it stores.
This example was specifically about gravitational potential energy, but it is not limited. We also have elastic potential energy. Take a spring, compress it and hold it. The spring wants to restore its position because it has much elastic energy to store. Moreover, this energy is due to a change in position.
Kinetic Energy
An object’s motion or movement in a closed system gives it its kinetic energy. Take the example of the book. It is on the table, storing some potential energy. Now, if it falls, all that potential energy will be converted slowly to kinetic energy, causing the motion of the book towards the floor. This motion indicates kinetic energy.
There are three types of kinetic energy.
Translational Kinetic Energy
The motion of an object in a straight and linear path from one position to another gives the object its translational kinetic energy. The book falling from the table involves translational kinetic energy, as the book falls in a straight line.
Other examples include something free falling due to gravity, a bullet being fired, and any motion in a straight line.
Rotational Kinetic Energy
Rotational motion in a circular path gives an object its rotational kinetic energy. It is also called angular kinetic energy.
Consider a wheel spinning around its axis. Now, as all the atoms are moving around the axis in a circular function ( they have some angular velocity ), the wheel is said to have rotational kinetic energy.
Vibrational Kinetic Energy
When an object is vibrating or shivering, it has vibrational kinetic energy.
For example, consider a cell phone that vibrates when it is ringing or a vibrating drum that is hit by a hammer; these vibrations are examples of vibrational kinetic energy.
How To Calculate the Gravitational Potential Energy?
To mathematically deduce the gravitational potential energy, we use the formula PE = mgh.
- PE is the potential energy
- m is the mass ( in kg )
- g is the gravitational acceleration of the earth ( 9.8 m/s2)
- h is the height of the object above the earth’s surface in metres (the position part we have been talking about)
Similarly, for kinetic energy, we have KE = ½ mv2.
- Kinetic energy is KE
- The mass of the object is m
- And the velocity per second is v
Mechanical energy is just the result of adding the potential and kinetic energy of an object. Joules is the unit of mechanical energy.
Conservation of Mechanical Energy
The total mechanical energy of an object remains preserved. We cannot create energy out of thin air, nor can we destroy it. It just gets converted from one configuration to another configuration. Imagine a roller coaster moving along a track; it has lots of kinetic energy due to its motion. Now, the roller coaster attains the peak of a climb and halts at the top in a stationary position. Thus, kinetic energy is the transformed potential energy over here.
Slowly, the roller coaster starts descending the opposite side. As it moves down, it gains speed, and the potential energy is transformed into an equivalent amount of kinetic energy. This goes on until you step out of the roller coaster.
The total mechanical energy of the roller coaster car did not change during the descents and peaks and descents. Moreover, no change was observed when kinetic energy was converted to potential energy and then back to kinetic energy; it remains the same (ideally, but there are always losses due to friction, resistance, and other dissipations).
The energy of the system is constant. We call it the Principle of Conservation of Mechanical Energy.
Conclusion
The turbines create water hydropower for windmills generating wind power. Mechanical energy is present and a meaningful, indispensable key to our daily lives.
Every day, we see mechanical energy in action as we pick up objects and throw them around, from playing the guitar to riding a bike. We cannot function without it.
