Fundamentals of Biomechanics

approach can convert this energy to kinetic
energy prior to release (Figure 6.17). In a
similar manner, in golf or tennis a forward
swing can convert the potential energy
from preparatory movement into kinetic
energy. A major application area of conservation
of energy is the study of heat or thermodynamics.
The First Law of Thermodynamics is
the law of conservation of energy. This is
CHAPTER 6: LINEAR KINETICS 153
Figure 6.16. Comparison of the kinetic energy (scalar) and momentum (vector) in a football collision. If you were
the running back, you would not score a touchdown against either defender, but the work done on your body
would be greater in colliding with the smaller defender because of their greater kinetic energy.
the good news: when energy is added into
a machine, we get an equal amount of other
forms of energy out. Unlike these
examples, examination of the next mechanical
energy (strain energy) will illustrate the
bad news of the Second Law of Thermodynamics:
that it is impossible to create
a machine that converts all input energy
into some useful output energy. In other
words, man-made devices will always lose