Introduction to Waves Resources: The Physics Classroom, Daniel A. Russell

What is a Wave? Wave: motion of a disturbance Disturbance creates waves that travel away from the source of the disturbance Waves transport energy, not matter. Mechanical waves require a medium: the elastic, deformable matter through which disturbance travels Electromagnetic waves don’t require a medium

Waves Transport Energy not Matter Long Tall

Types of Waves Pulse Wave: source is a non- periodic disturbance Periodic Wave: source is a periodic oscillation If source is Simple harmonic oscillation (SHO), wave form is sine wave Common forms: Transverse Longitudinal

Transverse Waves Medium moves perpendicular to direction wave travels Examples: Light, strings, seismic s-waves, water waves

Transverse Wave

Medium moves parallel (in line) to direction wave travels Longitudinal Wave Medium moves parallel (in line) to direction wave travels

Longitudinal Waves (cont.) Compression: where wave fronts are closer together than in undisturbed medium Rarefaction: where they are farther apart than in undisturbed medium

Longitudinal Wave

Other Waves

Quiz time! Not really, just some questions to check for your level of mastery.

Waves transport matter from one location to another without transporting energy. True False

Which diagram - A, B, C, or D represents the appropriate hand movements and patterns for a longitudinal wave?

If a longitudinal wave is created in a medium that extends horizontally from left to right, then the particles of the medium will vibrate in a ____ direction. Horizontal Vertical diagonal (both horizontal and vertical) circular none of these

Back to notes: Wave Parts The following words are used to describe waves: Amplitude Wave length Frequency Period Speed

Amplitude (A) How “tall” (or “wide”) the wave is Maximum displacement from the average or equilibrium position Crests: highs Troughs: lows Measured from “crest to rest” or “trough to rest” Unit of measure: meter

Amplitude and Energy

Wave Length (λ) Distance from a point on one wave to the same point on the next wave Unit of measure meter Graph of displacement versus distance is a “snapshot” of the wave at a given time

A wave is established in a rope A wave is established in a rope. The diagram below represents a snapshot of the pattern in the rope at a given instant in time. Several points on the rope are labeled with a letter. Identify the letters of any wave crests. List all that apply in alphabetical order with no spaces or commas between letters.

Frequency Frequency: number of cycles (repetitions) per unit of time (how often wave cycles) Units Hz (cycles/second)

Frequency (cont.) The higher frequency wave has more complete cycles in the same amount of time The upper wave has 2 x the frequency of the bottom. Note that the x-axis has units of time in this graph. Graph of displacement versus time shows the motion of a given position

Period (T) Period: Time for one complete wave to pass any given point Unit of measure seconds The period and frequency are reciprocals: T = 1/f f = 1/T

Wave Speed (v) Wave Speed: How fast a wave transmits energy from one place to another IMPORTANT: Wave speed depends only on specific properties of the medium) Constant for a given medium at given conditions Unit of measure meter/second Examples: Speed of wave in string depends on tension and linear density. Speed of wave in fluid depends on bulk modulus and density. Speed of wave in solid depends on elastic modulus and density.

Wave speeds vary widely: Wave Speed (cont.) Wave speeds vary widely: Water waves: a few miles per hour Sound (in air): about 340 m/sec or 1100 ft/sec (depends on temperature) Electromagnetic Waves (such as light) travel about 300,000,000 meters/sec or 186,000 miles/sec

A wave is moving through a coiled Slinky™ A wave is moving through a coiled Slinky™. The time for a single coil to complete one full back and forth vibration is known as the _____. a. speed b. period c. amplitude d. frequency

A long rope is vibrated on one of its ends in order to produce a wave A long rope is vibrated on one of its ends in order to produce a wave. A single point on the rope makes 4.0 complete vibrations every second. The quantity 4.0 refers to the _____ of the wave. a. speed b. period c. amplitude d. frequency

The wavelength of the wave is equal to _____. C

The amplitude of the wave is equal to _____.

Compared to the wave in Diagram B, the wave in Diagram A has _____. the same amplitude by a larger wavelength a larger amplitude and a smaller wavelength a smaller amplitude and the same wavelength the same amplitude and a smaller wavelength

Wave Properties (cont.) Here’s an example transverse wave showing some of the quantities we’ve talked about so far: 1 2 3 4 5 Answer: 2 complete wavelengths are shown How many complete wavelengths are shown?