# What kind of energy is always retained

## What is energy - physics - definition

### Principle of energy saving

One of the most wonderful properties of the universe is thatEnergy converted from one type to another andcan be transferred from one object to another . In addition, theTotal amount of energy always the same when transformed from one type to another and transferred from one object to anotherbecomes . It is one of the elementary properties of the universe.

In thermodynamics is expands the concept of energy to account for other observed changes, and thatPrinciple of conservation of energy is expanded to include a variety of ways in which systems interact with their environment. The energy of a closed system can only be achieved through energy transferthrough work orHeat can be changed . Based on the experiments of Joule and others, a fundamental aspect of the energy concept is thatEnergy is retained.This principle is calledfirst law of thermodynamics known . The first law of thermodynamics can be written in several forms:

In words:

Equation form:

∆Eint = Q - W.

It standsE.int for theinner energy of the material only datedStatus ofMaterials (Temperature, pressure and volume) depends.Q is theNet heat input to the system andW. is thisNetwork through work done the system. We must be careful and consistent in following the sign conventions for Q and W. Since W in the equation is the work done by the system, W is negative and E.int increases as the system is worked on.

Similarly, Q is positive for the heat added to the system. So when heat leaves the system, Q is negative. This tells us this: Theinternal energy of a system tends to increase as heat is absorbed by the system or when positive work is done on the system. Conversely, the internal energy tends to decrease when the system loses heat or when negative work is carried out on the system. It must be added that Q and W are path dependent, while Eint path-independent is.

Differential form:

dEint = dQ - dW

The internal energy Eint of a system tends to increase as energy is added as heat Q and tends to decrease as energy as work W done by the system is lost.