WAVES

COS 9.0, 9.1,9.2 WHAT YOU’LL LEARN Recognize that waves transfer energy. Distinguish between mechanical waves and electromagnetic waves. Explain the relationship between particle vibration and wave motion. Distinguish between transverse waves and longitudinal waves. Identify the crest, trough, amplitude, and wavelength of a wave. Solve problems involving wave speed, frequency, and wavelength Describe the Doppler effect Describe how waves behave when they meet an obstacle or pass into another medium. Explain what happens when two waves interfere. Distinguish between constructive interference and destructive interference. Explain how standing waves are formed.

What Is a Wave? wave: periodic disturbance in a solid, liquid, or gas as energy is transmitted through a medium. rhythmic disturbance that transfers energy. Anything that moves side to side, back and forth, or front to back carry energy through matter or space.

MEDIUMS substance or material (matter) through which a wave travels or is carried. solid, liquid, gas, or combination mechanical waves: wave that requires a medium through which to travel.

Waves travel through a medium such as: WATER AIR SOLIDS

Light Does Not Require a Medium electromagnetic wave: Wave which is capable of transmitting its energy through a vacuum (i.e., empty space) Visible light, infrared, x-rays, ultraviolet …

Waves & Energy Energy Ability to exert a force over a certain distance (work). Examples Waves rock a cruise ship Underwater earthquakes create tsunamis Hurricane wind driven waves. As they travel outward, spherical wave fronts get bigger, so energy in waves spreads out over a larger area.

Vibrations and Waves Most waves are caused by a vibrating object. Vibrations involve transformations of energy.

SIMPLE HARMONIC MOTION motion that occurs when an object is accelerated towards a mid-point. acceleration is dependent upon the distance of the object from the mid-point. Examples sea waves, pendulums, springs A wave can pass through a series of vibrating objects.

DAMPED HARMONIC MOTION vibration that fades out as energy is transferred from one object to another Examples shock absorbers, springs

Transverse Waves particles of medium move perpendicular to direction wave is traveling. can vibrate either up and down or back and forth. Examples Light waves Animation courtesy of Dr. Dan Russell, Kettering University

Longitudinal Waves wave in which the particles of medium vibrate parallel to direction of wave motion. Examples Sound waves

SURFACE WAVES occur at boundary b/w two different mediums, such as between water and air. particles move in circles. particles move both perpendicularly and parallel to the direction that the wave travels. cause most damage from earthquakes.

WATER WAVE

CHARACTERISTICS OF WAVES

Wave Properties Crest: highest point of a transverse wave. Trough: lowest point of a transverse wave. Amplitude maximum distance that the particles of a wave’s medium vibrate from their rest position.

Wave Properties

LONGITUDINAL Compressions: area of a longitudinal wave that pushed together Rarefactions: area of a longitudinal wave that begins to move forward

Wavelength distance from any point on a wave to an identical point on next wave. Not all waves have a single wavelength that is easy to measure. represented Greek letter lambda,.

Period time that it takes a complete cycle or wave oscillation to occur. symbol T.

FREQUENCY number of cycles or vibrations per unit of time. symbol is f. SI unit hertz. frequency is inverse of the period.

WAVE SPEED  how fast a wave moves speed depends on medium. In a given medium speed of waves is constant; it does not depend on frequency of wave.  v = velocity  = wavelength  f = frequency v f

WAVELENGTH

WORK: v = × f v = (3.2 m)(0.60 Hz) v = 1.92 m/s EXAMPLES Find the velocity of a wave in a wave pool if its wavelength is 3.2 m and its frequency is 0.60 Hz. GIVEN: v = ? = 3.2 m f = 0.60 Hz v f

WORK: f = v ÷ f = (5000 m/s) ÷ (417 m) f = 12 Hz EXAMPLES An earthquake produces a wave that has a wavelength of 417 m and travels at 5000 m/s. What is its frequency? GIVEN: = 417 m v = 5000 m/s f = ? v f

ELECTROMAGNETIC SPECTRUM full range of light at different frequencies and wavelengths

Doppler Effect observed change in frequency of a wave when source or observer is moving Pitch: how high or low it is, determined by frequency at which sound waves strike the eardrum in your ear. higher-pitched sound is caused by sound waves of higher frequency.

Doppler Effect

WAVE INTERACTIONS

Reflection bouncing back of a ray of light, sound, or heat when the ray hits a surface that it does not go through. free boundary travels in opposite direction to direction of original wave. fixed boundary waves reflect and turn upside down.

Diffraction change in direction of a wave when wave finds an obstacle or an edge, such as an opening.

REFRACTION bending of a wavefront as wavefront passes b/w two substances in which speed of the wave differs. All waves are refracted when they pass from one medium to another at an angle.

Interference combination of two or more waves of same frequency that results in a single wave. resulting wave can be found by adding height of waves at each point. Crests = positive troughs = negative.

CONSTRUCTIVE INTERFERENCE any interference in which waves combine so that resulting wave is bigger than original waves. increases amplitude by adding amplitudes of two individual waves

DESTRUCTIVE INTERFERENCE any interference in which waves combine so that resulting wave is smaller than largest of original waves. decreases amplitude when waves that have the same amplitude, the waves may completely cancel each other out. Interference of light waves creates colorful displays. Interference of sound waves produces beats.

Standing Waves pattern of vibration that simulates a wave that is standing still. form when a wave is reflected at the boundary of a medium. Although it appears as if the wave is standing still, in reality waves are traveling in both directions.

NODES Each loop of a standing wave is separated from next loop by points that have no vibration lie at points where crests of original waves meet troughs of reflected waves causes complete destructive interference.

ANTINODES form where crests of original waves line up with crests of the reflected waves, causing complete constructive interference. can exist whenever a multiple of half- wavelengths will fit exactly in length of the string.