What are waves?

WaveDefinition: A disturbance that transfers energy from place to place.What carries waves? A medium, a medium is the material through which a wave travels. A medium can be a gas, liquid, or solid.

Not all waves require a medium to travel.

Mechanical Waves are waves that require a medium.

Electromagnetic Waves travel through empty space and do not require a medium.

What causes waves?Waves are created when a source of energy causes a medium to vibrate.A vibration is a repeated back and forth or up and down motion.

How do waves carry energy?

Waves carry energy by displacement

The energy from this initial displacement causes the material nearby to also displace, which in turn displaces material near it... which creates a wave of energy propagating outwards. It is important to note that the material may move around as the wave passes, but it is the energy which is propagating outwards, not the material itself.

Lab: Slinkys in ActionUse a slinky to make different types of waves.Notice how the ribbon moves with each different type of wave.

Where did the energy come from to start the wave?

How could you tell the wave carried energy?

Types of waves: Waves are classified according to

how they move.

Transverse Wave

Teacher’s Domain Animation

Use a marker to trace a particles motion as the wave travels through the medium.How does the particle move with respect to the direction of the wave?

Transverse wave (sometimes called a sine

curve or wave)

Waves that move the medium at right angles to the direction in which the waves are traveling is called a transverse wave 3:15min.

Transverse means across. The highest parts are called crests the lowest parts are called troughs.

Draw & Label a Transverse Wave

Compressional or Longitudinal Wave

Matter vibrates in the same direction as the wave travels.Longitudinal discussion 3:36 min

Compressional or Longitudinal wave

The parts, where the coils are close together are called compressions, the parts where the coils are spread out are called rarefactions.

Teacher’s Domain animation

Draw & Label a

Compressional/Longitudinal Wave

Longitudinal & Transverse Wave Animation

Longitudinal & Transverse Wave Animation #2

Combinations of wavesSurface waves are a combination of transverse and longitudinal waves. The waves occur at the surface between water and air.

Surface Wave Animation

Summary of Waves

Summary of Waves - NASA Launch Pad Video Clip

Review, Review, Review…What does a wave carry?

How can waves be generated?

Compare and contrast a longitudinal and transverse wave.

Properties of Waves

Basic Properties of WavesAmplitudeWavelengthFrequencySpeed

AmplitudeAmplitude is the maximum (displacement) distance the particles of the medium carrying the wave move away from their rest positions.

The farther the medium moves as it vibrates the larger the amplitude of the resulting waves. The greater the amplitude the greater the amount of energy.

Amplitude of transverse waves

The amplitude of a transverse wave is the maximum distance the medium moves up or down from its rest position. You can find the amplitude of a transverse wave by measuring the distance from rest to crest or rest to trough.

Amplitude of a longitudinal wave.

The amplitude of a longitudinal wave is a measure of how compressed or rarefied the medium becomes.

Same frequencies, same wavelengths, different amplitudes, different energy

WavelengthA wave travels a certain distance before it starts to repeat. The distance between two corresponding parts of a wave is its wavelength.Transverse measure from crest to crest or trough to trough.Longitudinal measure from one compression to the next.

FrequencyThe number of complete waves that pass a given point in a certain amount of time.AKA number of vibrations per second.Frequency measured in hertz (Hz) named after Heinrich Hertz who discovered radio waves in 1886.

Frequency Animation

PeriodThe period of a wave is the time for a particle to make one complete cycle.

Pair Share1. Is there a relationship between

wavelength and frequency? What is it?

2. Is there a relationship between frequency and period? What is it?

3. Is there a relationship between amplitude and frequency? What is it?

1. Yes. A decrease in the wavelength increases the frequency and vice versa.

2. Yes. An increase in the frequency will increase the period and vice versa.

3. NO! Putting a lot of energy into a wave will not affect the wavelength, the frequency or the speed of the wave. The energy imparted to a wave will only affect the amplitude of that wave.

SpeedThe speed, wavelength, and frequency of a wave are related to each other by a mathematical formula.Speed = wavelength x frequencyFrequency = speed/wavelengthWavelength = speed/frequency

SpeedWhat can effect the speed of a wave?

Wave speed depends upon the medium through which the wave is moving. Only an alteration in the properties of the medium will cause a change in the speed.

SpeedWaves in different mediums travel at different speeds. However, in a given medium and under the same conditions the speed of the wave is constant.

1. A teacher attaches a slinky to the wall and begins introducing pulses with different amplitudes. Which of the two pulses (A or B) below will travel from the hand to the

wall in the least amount of time? Justify your answer.

They reach the wall at the same time. Don't be fooled! The amplitude of a wave does not affect the speed at which the wave travels. Both Wave A and Wave B travel at the same speed. The speed of a wave is only altered by alterations in the properties of the medium through which it travels.

2. The teacher then begins introducing pulses with a different wavelength. Which of the two pulses (C or D) will travel from the hand to the wall in the least amount of time ? Justify your

answer.

They reach the wall at the same time. Don't be fooled! The wavelength of a wave does not affect the speed at which the wave travels. Both Wave C and Wave D travel at the same speed. The speed of a wave is only altered by alterations in the properties of the medium through which it travels.

3. Two waves are traveling through the same container of nitrogen gas. Wave A has a wavelength of 1.5 m. Wave B has a wavelength of 4.5 m. The speed of wave B must be ________ the speed of wave A.a. one-ninthb. one-thirdc. the same asd. three times larger than

Answer: CThe medium is the same for both of these waves ("the same container of nitrogen gas"). Thus, the speed of the wave will be the same. Alterations in a property of a wave (such as wavelength) will not affect the speed of the wave. Two different waves travel with the same speed when present in the same medium.

4. TRUE or FALSE:Doubling the frequency of a wave source doubles the speed of the waves.

FALSE!The speed of a wave is unaffected by changes in the frequency.

5. A wave is introduced into a thin wire held tight at each end. It has an amplitude of 3.8 cm, a frequency of 51.2 Hz and a distance from a crest to the neighboring trough of 12.8 cm. Determine the period of such a wave.

Answer: 0.0195 secHere is an example of a problem with a lot of extraneous information. The period is simply the reciprocal of the frequency. In this case, the period is 1/(51.2 Hz) which is 0.0195 seconds.Know your physics concepts to weed through the extra information.

6. Frieda the fly flaps its wings back and forth 121 times each second. The period of the wing flapping is ____ sec.

Answer: 0.00826 secondsThe quantity 121 times/second is the frequency. The period is the reciprocal of the frequency.T=1/(121 Hz) = 0.00826 s

7. A tennis coach paces back and forth along the sideline 10 times in 2 minutes. The frequency of her pacing is ________ Hz.a. 5.0b. 0.20c. 0.12d. 0.083

Answer: DFrequency refers to the number of occurrences of a periodic event per time and is measured in cycles/second. In this case, there are 10 cycles per 2 minutes (also known as 10 cycles per 120 seconds). So the frequency isf =10 cycles / 120 s = 0.0833 cycles/s

8. Mac and Tosh are resting on top of the water near the end of the pool when Mac creates a surface wave. The wave travels the length of the pool and back in 25 seconds. The pool is 25 meters long. Determine the speed of the wave

GIVEN: d (1-way) =25 m, t (2-way)=25 sFind v.If the pool is 25 meters long, then the back-and-forth distance is 50 meters. The wave covers this distance in 25 seconds. Now use v = d / t.v = d / t = (50 m) / (25 s) = 2 m/s

9. The water waves below are traveling along the surface of the ocean at a speed of 2.5 m/s and splashing periodically against Wilbert's perch.

Each adjacent crest is 5 meters apart. The crests splash Wilbert's feet upon reaching his perch.

How much time passes between each successive drenching? Answer and explain using complete

sentences.

If the wave travels 2.5 meters in one second then it will travel 5.0 meters in 2.0 seconds. If Wilbert gets drenched every time the wave has traveled 5.0 meters, then he will get drenched every 2.0 seconds.

10.While hiking through a canyon, Noah Formula lets out a scream. An echo is heard 0.82 seconds after the scream. The speed of the sound wave in air is 342 m/s. Calculate the distance from Noah to the nearby canyon wall.

GIVEN: v = 342 m/s, t = 0.82 s (2-way)Find d (1-way)If it takes 0.82 s to travel to the canyon wall and back (a down-and-back time), then it takes 0.41 s to travel the one-way distance to the wall. Now use d = v • td = v • t = (342 m/s) • (0.41 s) = 140 m

Chapter 15 -3

Ways Waves InteractReflectionRefractionDiffractionInterference

ConstructiveDestructive

Standing Waves

ReflectionWhen an object or wave hits a surface through which it cannot pass, it bounces back.

Angle of incidenceAngle of reflection

Examples of reflectionMirrorEchoBall against a wall

Refraction is when a wave moves from one medium

into another medium at an angle, it changes speed as

it enters the second medium which causes it to

bend. The bending of waves due to a change in speed is called refraction.

RefractionThough all waves change speed when they enter a new medium. Bending occurs when one side of the wave enters the new medium before the other side

DiffractionWhen a wave passes a barrier or moves through a hole in a barrier it bends and spreads out.

InterferenceConstructive interference occurs whenever two waves combine to make a wave with a larger amplitude.

Destructive interference when the amplitudes of two waves combine producing a smaller amplitude.

Standing waves:If the incoming wave and the reflected wave combine at the right places the combined wave appears to be standing still.It appears to be standing in one place, even though it is two waves interfering as they pass through each other.Brightstorm video 9:45 min

Nodes and AntinodesNodes: at certain points, destructive interference causes the two waves to combine and produce an amplitude of zero.

Antinodes are the points of maximum energy. The crests and troughs of a standing wave.

ResonanceMost objects have a natural frequency of vibration. Resonance occurs when vibrations traveling through an object match the object’s natural frequency.An object that is vibrating at its natural frequency absorbs energy from the objects that vibrate at the same frequency. Occurs in music.