Conservation of energy
Conservation of energy
Conservation of energy is a useful principle / law that tells us the energy of a system will remain constant (barring any input or removal of energy). By careful accounting, we can use conservation of energy to solve a wide range of practical physics problems.
For example, we can imagine a mass that moves up a hill and then slides down the other side. In such a situation, as the mass goes up the hill it gains gravitational potential energy. As it slides down the other side, it is trading the gravitational potential energy for kinetic energy. Such trades between different forms of energy are a good way to understand and quantify the motion of many systems of interest. It is, for example, the principle of operation behind things like roller coasters.
Energy is present in a system and can take different forms.
A system composed of only a single object can only have kinetic energy. On the other hand, a system that contains objects that interact via conservative forces or that can change its shape reversibly may have both kinetic and potential energies.
Conservation of energy
Mechanical energy is the sum of a system’s kinetic and potential energies. Any change to a type of energy within a system must be balanced by an equivalent change of other types of energies within the system or by a transfer of energy between the system and its surroundings.
A system may be selected so that the total energy of that system is constant.
If the total energy of a system changes, that change will be equivalent to the energy transferred into or out of the system.
Selection of a system determines whether the energy of that system changes.
Energy is conserved in all interactions. If the work done on a selected system is zero and there are no nonconservative interactions within the system, the total mechanical energy of the system is constant.
However, if the work done on a selected system is nonzero, energy is transferred between the system and the environment.
See also
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