THE mechanical energy it can be defined as the capacity of a body to do work. When this ability to do work is related to movement, it is called kinetic energy. However, if the ability to do work is related to the position of a body, it is called potential energy.
Kinetic energy
This form of energy is related to the mass and speed of a body. Mathematically, it is given by the equation:
ANDcin = mv2
2
Being:
m – body mass;
v – speed.
We can see from the equation above that if the velocity is zero, the body will have no kinetic energy. This proves what the definition of this form of energy says, which describes it as the energy associated with the movement of bodies.
Another conclusion that we can draw from the equation is that the kinetic energy will always have positive values, since the mass is always positive, and if the velocity has a negative value, when squared it will result in a value positive. Thus, the mv product2 it will always be positive.
Potential energy
To better understand the definition of potential energy, see the figures:
The block is suspended by a string, so if we cut it, the block will fall. During the movement of the fall, it will perform work
The block is attached to a spring compressed by a string so that, if the string is cut, the block will be thrown forward, doing work
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In both cases, the block will have the capacity to carry out work, due to the energy stored by the position in which it is found. Stored energy is called potential energy and can be of two types:
Gravitational potential energy: when energy originates from the Earth's gravitational pull on an object. This is the case of the first figure, where the block is suspended by the wire. If the wire is broken, there will be free fall movement. This form of energy depends on the height of the body, its mass and local gravity. Mathematically, it is calculated with the equation:
ANDpg = mg.h
Being:
m – body mass;
g – gravity acceleration on site;
h – height in which the body is in relation to a certain reference.
Elastic potential energy: it originates in the action that a spring can exert on the body. For example, in the second figure, where the block is attached to a spring compressed by a wire, if this wire is cut, the spring will stretch and push the block forward, causing it to perform work. Elastic potential energy depends on the spring constant and displacement. It is defined by the expression:
ANDby = 1 k x2
2
Being:
k – the elastic constant of the spring;
x – spring displacement.
By Mariane Mendes
Graduated in Physics
Would you like to reference this text in a school or academic work? Look:
TEIXEIRA, Mariane Mendes. "What is mechanical energy?"; Brazil School. Available in: https://brasilescola.uol.com.br/o-que-e/fisica/o-que-e-energia-mecanica.htm. Accessed on June 27, 2021.