Class notes #1
In our first class we discussed engineering careers and some of the mechanical aspects of
the class. This was for your information; none of it will be ‘on the test’.
The four fundamental forces
We discussed the four fundamental forces of classical physics:
The strong force, responsible for holding together quarks in subatomic particles
like the proton.
The electromagnetic force, responsible for holding atoms together, as well as
bonding atoms together into molecules, and molecules together into solids. This is
the force that mediates the attraction between positive and negative charge, and is
the basis for all of electrical engineering, from radio to computers.
The weak force, responsible for holding the atomic nucleus together
Gravity, the very weak force that nevertheless holds the stars and planets together,
and keeps us from floating off into space.
These forces differ in their strength (they are listed in stronger to weaker order above)
and effective range. The strong and weak forces only act at very short ranges comparable
to the size of an atomic nucleus and are of little relevance to our task at hand. Both the
electromagnetic and gravitational forces act over large distances, and they also share
some other common characteristics.
The magnitude of the forces due to gravity,
, and the static electric force,
described by similar looking equations. Both depend inversely on the square of the
, between the two bodies. Both contain a physical constant,
, for gravity, and
for the electromagnetic force. Both also depend on the product of some physical
property of the two bodies; the mass,
(measured in kilograms), for gravitation and the
quantity of charge,
(measured in coulombs)
for the electrical force. A key difference is
that mass is always positive, while charge can be either positive or negative. This has
important implications: the gravitational force is always attractive, while the electrostatic