Work and Energy theory
Work and Energy theory
Definition of Work and Energy
Energy is the property that bodies have and allows them to make changes in themselves or in other bodies. His unit in the International System is the joule (J).
There are different forms of energy:
- Mechanics (kinetic, potential, elastic)
On Physics has nothing to do with physical exertion work. To do a work in physics involves applying a force on a body and move it. As a result of this action, the work is a way of transferring energy from one body to another.
Work is a scalar physical quantity is represented by the letter W (English Work) and expressed in energy units, this is in joules or joules (J) in the International System.
Is the energy that bodies have due to their movement. It is defined as the need to accelerate a body having a given mass from rest to the speed indicated.
Once this energy has been gained during acceleration, the body maintains its kinetic energy unless its speed changes. For the body, to return to its resting state it is required a negative work of the same magnitude as its kinetic energy.
It is the energy that measures the ability of the system to perform work solely according to its position or configuration. It may be present as:
- Gravitational potential
- Electrostatic Potential
- Elastic Potential
It is the energy acquired by a body when a work is performed on it at a certain height. That is, it is the sum of the kinetic and potential energies.
It is impossible to observe the mechanical energy in an object. However, we can study the mechanical energy when it is transformed from one to another or when it is transferred from one place to another.
When a body falls, potential energy it loses, is the kinetic energy it gains, but the sum of kinetic and potential energy remains constant. This only occurs in the absence of friction. If there is friction, part of the mechanical energy is dissipated as heat.
Degradation of energy
Energy is neither created or destroyed, it’s only transformed. In any process, the total amount of energy in the universe remains constant. However, the quality of this energy decreases. This means that after each transformation energy is less profitable for further transformations: energy is degraded.
It is a fact that some forms of energy are more profitable than others. For example, the kinetic energy is of high quality because it can be transformed into mechanical energy, radiant energy or thermal energy.
By contrast, the thermal energy is a low-quality energy. It appears in all energy transformations, but with little or no ability to perform new transformations and produce useful changes in bodies. Therefore, we say that heat is a form of degraded energy.
Being φ the angle between F and s
If the force is variable and/or the trajectory is not rectilinear
Gravitational potential energy
Elastic potential energy
Mechanical energy in the absence of friction
Variation of mechanical energy in the presence of friction
Being WFR the work done by the frictional force
Impulse of a force, which acts during a time t on a body
Energy conservation law
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