PowerPoint #5: Basic Physical Laws Governing Energy Use. Basic Physical Laws Governing Energy Use. Forms of energy Energy units Energy, work and power Conservation of energy Energy conversion and efficiency Newton’s laws of motion. FORMS OF ENERGY. Chemical
Basic Physical Laws Governing Energy Use
Velocity, relative position, temperature and mass
1. Velocity: Energy associated with object’s motion is called kinetic energy (KE):
KE = (1/2)mv2
Units: E(joule) = m(kg)v2(m/sec)2 = kg meter2/sec2
2. Relative position: Energy associated with location of object relative to some reference point, such as surface of earth, or center of earth. Called potential energy (PE):
PE = mgh
g = acceleration due to gravity (meter/sec2)
Work done on a system plus heat added to a system = the change in total energy of the system
Won + Qto = (KE+PE+TE)
Won = work done on the system
Qto = heat added to the system
Implication of First law: 1) energy cannot be created or destroyed; 2) total amount of energy in universe is constant.
Efficiency (%) = useful energy out x 100 total energy in
Efficiency = ( 1- heat out/heat in) x 100 % from first law. But, second law says that heat out is always less than heat in, if useful work is to be extracted from the process.