Energy does not simply appear and disappear. Energy is transferred from one position to another or transformed from one type of energy to another.

EO 1.4STATE the First Law of Thermodynamics, "Conservation of Energy."

Conservation of Energy

The First Law of Thermodynamics is simply stated "energy cannot be created or destroyed, only altered in form." In the previous chapter, we discussed potential energy, where a force is applied to an object, raising it from some point of origin to some height. The energy expended in raising the object is equivalent to the potential energy gained by the object because of its height. This is an example of a transfer of energy as well as an alteration of the type of energy. Another example is throwing a baseball. While the ball is in your hand, it contains no kinetic energy. You apply a force to the ball by throwing it. The ball leaves your hand with a velocity, giving it kinetic energy equal to the work applied by your hand. Mathematically, this can be described by the following simplified equation.

where:

is energy initially stored in an object/substance. This energy can exist in various combinations of kinetic energy and potential energy.

Energy_added is energy added to the object/substance. Heat can be added. Energy can be added in the form of stored energy in any mass added, such as water to a fluid system. Work can be done on a system. Heat is energy gained or lost at a microscopic level. Work is the same at a macroscopic level.

is energy removed from an object/substance. Heat can be rejected. Work can be done by the system. This energy can be in the form of energy stored in any mass removed.

Energy_final is energy remaining within the object/substance after all energy transfers and transformations occur. This energy can exist in various combinations of kinetic, potential, flow, and internal energy.

To further describe each of the components of the above equation, each component can be broken down as follows:

, = KE₁ + PE₁

Energy_added = Work done on and heat added to the system

= Work done by and heat removed from the system

Energy_final = KE₂ + PE₂

The resulting energy balance is provided in Equation 5-5.

Neglecting any heat removed or added to a system, we can replace E_added and E_removed in Equation 5-5 with their associated work terms to obtain Equation 5-6.

The final energy balance is called a "simplified energy balance." Any energy balance is a statement of the Law of Conservation of Energy. In this simplified form, the balance applies only to mechanical problems, since we neglected heat. However, more specific energy balances that include heat will be discussed in other Fundamental Manuals. For example, specific energy balances for flow systems will be discussed in the Heat Transfer, Fluid Flow, and Thermodynamics modules.