1D: Sound, Waves,
Symmetry & Vision
Simplified 1D covers
Volume 1, the freshman course, of The Feynman Lectures
on Physics. The topics we explore include:
- Angular Momentum
- Moments of Inertia
- Rotations in Three-Dimensions
- Sound & Beat Frequencies
- Modes & Harmonics
- Fourier Series & Transforms
- Complex Waves
- Symmetry Properties of Natural Laws
waves are created by a source moving faster than the wave velocity.
Consider the example of a jet flying faster than the speed of sound in
air. At each point P along the jet’s path, the jet compresses the air
in front of it, creating a pressure wave that spreads outward in all
directions at the speed of sound, cs.
46-1 shows the crests of pressure waves emitted at equally spaced
times. All such waves will be tangent to a common line, thus creating a
Jet (grey) Creating Bow Wave
An Intense Conical Wave With Half-Angle θ
notes that a bow wave is created whether or not the jet itself makes
any sound — sound is created by the mere act of moving through air
faster than the speed of sound. The next figure clearly illustrates a
bow wave coming from a bullet.
are not sources of sound in and of themselves; it is their high-speed
passage through air that creates sound waves.