1. Chapter 14: Vibrations and Waves Notes

2.  Periodic motion is a motion that is repeated in a regular cycle.  Oscillatory motion is the movement of an object back and forth between two opposing points. This is a type of periodic motion because these objects follow the same path in the same amount of time.  Examples: mass on a spring, a mass on a pendulum, vibrating guitar string, and a tree swaying in the wind  Simple harmonic motion happens in any system where the force acting to restore the object to its equilibrium position is directly proportional to the displacement of the object shown. (restoring force gets bigger as the distance gets bigger) Periodic Motion

3. Equilibrium Position: Where it comes to rest. Restoring force tries to return it to equilibrium. Period (T) – time to repeat one complete cycle of motion Amplitude (A) – the maximum distance the object moves from equilibrium. Net force is zero at equilibrium and non-zero when the object is not in equilibrium. EPE when it is stretched or compressed. Kinetic Energy (KE when it moves between the two extremes.

4. Periodic Motion

5.  Resonance occurs when forces are applied to a vibrating or oscillating object at equal time intervals which makes the amplitude of the wave bigger, like when a friend pushes you on a swing  Resonance is used in musical instruments to amplify sound and in clocks to increase accuracy  EX Tacoma Narrows Bridge 1940 https://www.youtube.com/watch?v=lXyG68_caV4 Start at 2:04. https://www.youtube.com/watch?v=lXyG68_caV4 Periodic Motion

7.  Waves combine harmonic motion and linear motion.  A wave carries energy through matter or space without transferring matter.  Waves that travel through a physical medium such as water, air, or a rope.  A wave pulse is a single bump that travels through a medium (like shaking a rope once). However, if the disturbance continues at a constant rate, a periodic wave is generated (like shaking the rope multiple times). Mechanical Wave Properties

8.  Transverse Waves – a slinky moving up and down/ side to side  The disturbance is perpendicular to the wave motion.  Longitudinal wave – a slinky being pushed or pulled  The disturbance is parallel to the wave motion.  Ex: Sound waves  Surface wave – like the waves in the ocean  The disturbance follows a circular path that is sometimes parallel and other times perpendicular to the wave’s motion. Mechanical Wave Properties

11.  The speed of a mechanical wave depends only on the medium it passes through.  Incident wave – the pulse that strikes the boundary.  Reflected wave – the wave that returns after striking a boundary.  Damping – the gradual reduction of a wave’s amplitude (the wave dying out). Wave Behavior

12. Boundaries: Soft Boundary – the wave’s energy dies out (damping) Ex: yelling into a pillow Rigid Boundary -the reflected wave returns after striking a boundary at the same speed but is inverted. Ex: Echos Changing mediums – Refraction happens when a wave bends as it enters a boundary made of a different medium. Ex: Light entering water Corners Diffract – Diffraction happens when a corner drags the wave slowing it down and turning it. Ex: Light

13.  Principle of Superposition states that two waves can combine to form a new wave.  The result of two waves combining is interference.  Constructive Interference is when two waves combine to form a larger wave.  Destructive Interference happens when two waves combine to form a smaller wave. Wave Behavior

14.  A wave that is trapped between two boundaries that give energy to the wave is called a standing wave.  Antinode – the places of greatest amplitude  Node – places of no amplitude  2 antinodes equal 1 wavelength 2AN = 1λ Wave Behavior 1 wavelength

15.  Picturing waves in two dimensions (2D): Think of throwing a pebble into still water.  Wavefront – a line that represents the crest of a wave in two dimensions.  The circles show the wavefronts.  When drawn to scale, the show the wavelength of the wave.  Ray - A line drawn at a right angle to the wavefront to show the direction the wave travels. Wave Behavior

16.  Law of reflection: the angle of incidence is equal to the angle of reflection. Wave Behavior