Thermodynamics
ENERGY, WORK, AND HEAT
In most practical engineering calculations, the acceleration due to gravity (g) is numerically equal
to the gravitational constant (gc); thus, the potential energy (PE) in foot-pounds-force is
numerically equal to the product of the mass (m) in pounds-mass times the height (z) in feet
above some reference level.
Example:
Determine the potential energy of 50 lbm of water in a storage tank 100 ft above the
ground.
Solution:
Using Equation 1-11
PE
mgz
gc
PE
(50 lbm) (32.17 ft/sec2) (100 ft)
32.17 ft lbm/lbf sec2
PE
5000 ft lbf
Kinetic Energy
Kinetic energy (KE) is the energy of motion. Using English system units, it is defined by
Equation 1-12.
(1-12)
KE
mv2
2gc
where:
KE
=
kinetic energy (ft-lbf)
m
=
mass (lbm)
v
=
velocity (ft/sec)
gc
=
gravitational constant = 32.17 ft-lbm/lbf-sec2
Rev. 0
Page 15
HT-01
