What is a wave? A wave is any disturbance that transmits ENERGY through matter and space. Waves carry energy NOT matter.

Waves and Energy MECHANICAL WAVES Require a medium to travel through. Need matter to pass the energy from place to place Example: Waves from hurricane IKE

What is a Medium? A substance through which a wave can travel Water People Air Coiled wire

Waves and Energy ELECTROMAGNETIC WAVES Carry energy but do not need a medium to travel through.

How is the energy transferred? Energy is transferred from particle to particle in the medium Energy propagates (travels) but the particles (media) do not

Longitudinal (Compression) Waves Longitudinal/ Compressional Waves The material that the wave is in vibrates back and forth along the path that the wave travels. Direction of wave Movement of molecules associated with wave.

Longitudinal (compression) waves are in the same direction as, or parallel to, the direction of the wave. Direction of wave Movement of molecules associated with wave.

Sound is a longitudinal wave. Direction of wave Motion of air molecules associated with sound.

A slinky produces longitudinal (compression) waves.

Transverse Waves Transverse Wave The material that the wave is in moves perpendicular (at right angles) to the direction that the wave is traveling. Direction of wave Direction of particles

A transverse wave vibrates perpendicular to the direction of the wave. Direction of wave Direction of particles

Direction of wave Water waves are transverse waves. If you were in the water you would bob up and down. You would be a particle in the wave. However, the wave is moving toward the shore. Direction of particles

Direction of wave Transverse Wave Direction of particles

Examples of transverse waves: water waves TAKS illustration “the wave” TAKS illustration light waves

Parts of a Wave Longitudinal (Compressional) Compression Rarefaction Wavelength Transverse Crest Trough Amplitude Wavelength

Parts of a Longitudinal Wave Compression Section of a longitudinal wave where the particles are crowded together Rarefaction Section of a longitudinal wave where the particles are less crowded than normal

The highest part of the wave is the crest. The lowest portion of the wave is the trough. crest trough

Parts of a Transverse Wave Amplitude – Maximum distance the wave vibrates from its rest position

Which one of these waves has a larger amplitude?

Parts of a Wave Wavelength (λ) The distance from any point on one wave to that same point on the next wave λ λ

A wavelength can be measured from crest to crest, trough to trough, or any other place where the wave pattern repeats itself. A wavelength is represented by the Greek letter lambda (λ). Wavelength

Which one of these waves has a larger wavelength ( λ) ?

Measurable Characteristics of Waves

The frequency of a wave is the number of complete wave cycles it makes each second. Frequency of a wave 1 wave cycle per second = 1 hertz Frequency is measured in hertz (Hz). You can find this and all formulas that you need on the TAKS formula chart! High frequency – more cycles per second. Low frequency – fewer cycles per second.

Which one of these waves has a higher frequency?

Measurable characteristics Velocity(m/s) Velocity remains the same in the same media Velocity of a wave differs depending on the medium it travels through and the energy the wave has. Velocity will change if it enters a new form of matter Velocity = frequency x wavelength

The velocity of a wave = frequency x wavelength V = fλ

Measurable Characteristics PERIOD (T) The time taken to complete one cycle The mathematical inverse of the frequency Usually measured in seconds

The velocity of a wave is frequency x wavelength V = fλ. Frequency is measured in hertz. We have all the information we need to answer the question! 2Hz x 1m = 2 8 Hz x 2m = 16 3Hz x 3m = 9 1 Hz x 4m = 4 Released TAKS Question: Copyright © and trademark ™ All Rights Reserved.

Remember, a wavelength is the distance between points where the wave pattern repeats itself. In this picture, the only possible wavelength choice is crest to crest. Released TAKS Question: Copyright © and trademark ™ All Rights Reserved.

Interference What happens when a wave hits something?

Measurable characteristics Velocity(m/s) Velocity remains the same in the same media Velocity of a wave differs depending on the medium it travels through and the energy the wave has. Velocity will change if it enters a new form of matter Velocity = frequency x wavelength

Refraction A wave that bends when transmitted into a new media. The wave will change direction (refract). Why? Each media transports the wave at a different velocity Frequency stays the same, therefore wavelength changes (which causes the bend)

Diffraction The bending of waves around obstacles or through an opening or slit.

What happens to reflected waves? Inverted reflected wave passing from a less dense material to a more dense material. Erect reflected wave passing from a more dense to a less dense material.

What happens when 2 waves meet each other?

How to predict wave interference… Align the waves in time and add the amplitudes. Amplitudes can be either positive or negative. If the amplitudes are of the same sign, the wave is reinforced and gets larger. If the amplitudes are of opposite sign, the wave is diminished and gets smaller.

Types of Interference Constructive Destructive

Interference When waves combine Constructive interference – when waves combine so that the resulting wave is bigger than the original waves. Destructive interference – when waves combine so that the resulting wave is smaller than the largest of the original waves.

Constructive Interference When two waves crossing paths are superimposed and the resultant waveform has a larger amplitude than each of the individual waves.

‘The Wedge’ is a case of constructive interference causing huge localized waves

Destructive interference 2 waves are superimposed and the resultant has a smaller amplitude than either of the individual waves Complete Destructive Interference – amplitudes of individual waves cancel one another out.

Comparing the two

The Physics Of Sound Why do we hear what we hear? (Turn on your speakers)

What are sound waves? Mechanical waves Sound waves require a medium to transport them Sound waves (pulsate) create vibrations causing changes in pressure

What are sound waves? A longitudinal wave caused by pressure fluctuations in vibrating objects: –Compressions: high pressure regions (crowded area) –Rarefactions: low pressure regions (relaxed area) –Frequency- # of compressions passing/second –Wavelength – distance between compressions –A 3-dimensional arrangement

Sound in different types of media? Each substance transfers sound energy at a different rate The rate is dependent on: Tension between the molecules- higher the tension the faster sound travels through a medium. thermal energy - higher the temperature, the faster the molecules move and allow sound to travel through a medium.

The ear…a sound detector? Collects and directs sound Vibrates and send to the middle ear Lever system that amplifies sound vibrations Vibration of tiny hairs, transmitted to brain by nerves

The three components of sound are: Pitch (how high or low) Loudness (volume) Timbre (tone color)

Frequency vs. Pitch Pitch is the perceived human highness or lowness of a sound –A qualitative observation (how high or low) –derived from the frequency Frequency is the measurable quantity –The quantitative observation –Measured in Hertz The higher the frequency, the higher the pitch Demonstration: striking different tuning forks

When the frequency of a sound doubles we say that the pitch goes up an octave. We can hear a range of pitches of about ten octaves. Many animals can make sounds and hear frequencies that are beyond what we can hear.

What frequencies can humans hear? Human Range (audible) 20 Hz - 20,000 Hz We hear best between 200 and 2000 Hz Changes with age and damage to the ear Ultrasonic –Anything above 20,000 Hz Used for sonar and medical diagnosis Infrasonic Anything below 20 Hz Heavy machinery, lightning, elephants We might not hear it, but you may feel these

Amplitude vs. Loudness Loudness is the perceived human volume of sound –A qualitative measure of the power in a wave –Can be quantified using “decibels” –derived from the amplitude Amplitude is the measurable quantity –The quantitative observation –Measured in meters The larger the amplitude, the more energy in a wave and the more powerful it is.

Loudness vs. Decibel Source of SoundDecibels Boeing Civil Defense Siren130 Jack Hammer120 Rock Concert110 Lawn Mower100 Motorcycle90 Garbage Disposal80 Vacuum Cleaner70 Normal Conversation60 Light Traffic50 Background Noise40 Whisper30

Timbre (Tone) Harmonic Content of sound Attack and Decay of sound Vibrato –Periodic changes in the frequency/amplitude

The of sound….

Diffraction of Sound

Refraction of Sound

Resonance When one object vibrating at the same natural frequency of a second object forces that second object into vibrational motion

Doppler Effect N5tlIhttp:// N5tlI

Doppler Effect observed –Definition: relative motion creates an observed change in frequency

Doppler Effect –as object moves toward a stationary observer: Perceive a higher pitch (frequency actually does not change) –as object moves away from a stationary observer: Perceive a lower pitch (frequency actually does not change)

Doppler Effect