Total energy is made up of kinetic energy, gravitational potential energy and internal energy (related to molecular motion and intermolecular forces). The work term is generally split up into its two components: shaft work (energy transferred from external sources) and flow work (the summation of work done on the fluid at point 1 and work done by the fluid at point 2):
Individual terms in a physical equation such as this can only be added or subtracted if they have identical dimension. Check for yourself that each term in this equation has dimension of energy (Joules or kgm2s-2). This equation can also be written in terms of specific energy, J/kg, by dividing by mass:
The energy equation is applied in its most convenient form and terms are removed or expanded upon as required. Each practical will demonstrate the versatility of this fundamental engineering equation.