What is a wave?

• A disturbance that travels through a medium from one location to another location – A medium is a substance or material which carries

the wave

General definitions of vibrations and waves

• Vibration: in a general sense, anything that switches back and forth, to and fro, side to side, in and out, off and on, loud and soft, or up and down is vibrating. A vibration is a wiggle in time.

• Wave: a wiggle in both space and time is a wave. A wave extends from one place to another.

• Vibrations and waves: the source of all waves is something that is vibrating. Waves are propagations of vibrations throughout space.

Waves• When you drop a ball into water, some of

the water is pushed aside and raised by the ball.

Parts of a wave

• You can think of a wave as a moving series of high points and low points.

• A crest is the high point of the wave.• A trough is the low point.

Parts of a wave• The frequency of a wave is the rate at which

every point on the wave moves up and down. • Frequency means “how often”.

Examples of Frequency

• What is the frequency of the second hand of a clock?

Frequency = 1cycle/60 secFrequency = 1cycle/60 sec Period = 60 Period = 60 secsec

What is the frequency of US Presidential elections?What is the frequency of US Presidential elections?

Frequency = 1 election/4 yrsFrequency = 1 election/4 yrs Period = 4 Period = 4 yrsyrs

Parts of a wave

• The amplitude of a wave is the maximum height the wave rises above the level surface.

Parts of a wave• Wavelength is the distance from any point on a wave

to the same point on the next cycle of the wave.• The distance between one crest and the next crest is

a wavelength.

Wave PropertiesPeriod

The wave period, P, this the time it take one wave to pass the observer.

• When oscillations are small, the motion is called simple harmonic motion (shm) and can be described by a simple sine curve.

The speed of waves

• A wave moves one wavelength in each cycle.

• Since a cycle takes one period, the speed of the wave is the wavelength divided by the period.

The speed of waves• The speed is the distance traveled (one wavelength)

divided by the time it takes (one period). • We usually calculate the speed of a wave by

multiplying wavelength by frequency.

Wave Motion, Speed, Type Waves to transfer energy, not matter, from one place to

anotherA Vibrating source transfers a disturbanceSpeed depends on type of vibrating source and medium

through which it travelsWave speed = f x The same type of wave moves at the same speed regardless of f or

For any wave, f is inversely proportional to

Wave TypeTransverse waves vibrate across from

direction of travelLongitudinal waves vibrate along the

direction of travel (as in a spring)

Longitudinal

• Vibrates parallel to (in the same direction of) wave travel – sound waves

– the other end of the medium without the actual movement of matter

Animation courtesy of Dr. Dan Russell, Kettering University

Animation courtesy of Dr. Dan Russell, Kettering University

Longitudinal

• Use a Slinky to demonstrate a longitudinal wave: – Work with a partner– Stretch it out along the table– One of you grasp and draw several coils of a stretched

Slinky toward yourself – Release the coils– The other student must hold his or her end of the Slinky

still– A longitudinal wave pulse will be generated and travel

down the length of the Slinky.

24.2 Longitudinal waves• The oscillations of a longitudinal wave are in

the same direction that the wave moves.

Longitudinal

• Are composed of – Compressions, where the parts of the medium

(coils of the Slinky) are closer together than normal

– In this investigation, you created (generated) compressional longitudinal waves

– The waves traveled through a media (the slinky)

Longitudinal

• Are composed of – Rarefactions, where the parts of the medium are

farther apart than normal– In this demonstration, you created (generated)

rarefactional longitudinal waves– The waves traveled through a media (the slinky)

Sound Waves

Molecules in the air vibrate about some average position creating the compressions and rarefactions. We call the frequency of sound the pitch.

Wave Interference

When two wave pass each other their superpositioncauses reinforcement or cancellation.

Constructive interferenceReinforcement when the crest of one wave

overlaps the crest of another Their individual effects adds together,

resulting in a wave increased in amplitude

Destructive InterferenceCancellation when crest of one wave overlaps trough of

another reducing their individual effectsWater waves show these best

Out of phase- the crest of one wave arrives at a point at the same time as a trough of the second wave arrives, effects cancel each other In phase- two waves crests and troughs arrive at a place at the same time, effects reinforce each other

Sound Wave Interference

•Interference occurs when two sounds of difference frequency are heard superposed. •Constructive interference causes louder sound and destructive inference cause fainter sound.•This alternating pattern produces a beat. A piano tuners listens for beats to disappear.

Standing WavesOccurs when a wave reflects upon itself and

interference causes the patternNodes remain stationary

Anti nodes-occur half way between nodes

Standing WavesChange the frequency in a standing wave and more nodes/antinodes appear in the event

The Doppler effect-Change in frequency due to the source or receiver the

greater the speed of the source, the greater the Doppler effect

Stationary bug

Bug swimming

Blue Shift-increase in frequency Red Shift- Decrease in frequency

Doppler Shift Gives Radial Velocity

Radar

True Velocity

Tangential Velocity

Radial Velocity

Shock Waves Produced by supersonic aircraft,

three-dimensional cone shaped Sonic boom – sharp crack heard

when conical shell of compressed air that sweeps behind a supersonic aircraft reaches listeners on the ground below.

What dictates the frequency of a sound wave?

(a) wavelength(b) medium(c) source of the sound(d) speed(e) amplitude

(c) source of the sound

For a medium transmitting a longitudinal wave, the areas of the medium where the density of the medium is temporarily

increased are called...

(a) rarefactions(b) compressions(c) density holes

(b) compressions

Sonic booms from a plane are produced...

(a) because the plane breaks through the sound barrier.

(b) when the plane reaches the speed of sound.

(c) by the plane traveling faster than the speed of sound.

(d) by the plane traveling slower than the speed of sound.

(c) by the plane traveling faster than the speed of sound

When you move away from a fixed source of sound, the

frequency of the sound you hear...

(a) is greater than what the source emits

(b) is less than what the source emits

(c) is the same as what the source emits(b) is less than what the source emits

- slower than the speed of soundSubsonic

• Supersonic - faster than the speed of sound

Mach Number =speed of sound

speed of object

Transverse

• Vibrates perpendicular (at right angles) to the wave travel – Electromagnetic waves

Animation courtesy of Dr. Dan Russell, Kettering University

24.2 Transverse waves

• The oscillations of a transverse wave are not in the direction the wave moves.

Transverse

• Use a Slinky to demonstrate a transverse wave:– Work with a partner– One of you move your end of the Slinky back and forth

(left and right, like a snake crawling), perpendicular to its stretched length.

– The other student must hold his or her end of the Slinky still

– A series of transverse waves will be generated and will travel through a medium (Slinky)

Electromagnetic Waves

• Wave which is capable of transmitting its energy through a vacuum (i.e., empty space)

• Produced by the vibration of electrons within atoms on the Sun's surface

• Travel through space until they reach Earth These waves subsequently travel through the vacuum of outer space, subsequently reaching Earth

What determines the speed of a wave?

(a) the frequency(b) the wavelength(c) the amplitude(d) the period(e) the medium of transmission

(e) the medium of transmission

Water Waves

• A combination of longitudinal & transverse

Animation courtesy of Dr. Dan Russell, Kettering University

A skipper on a boat notices wave crests passing his anchor chain every 5 seconds. If the wave

crests are 15 m apart, what is the

speed of the water waves in m/s? (a) 5 (d) 10

(b) 15 (e) 3(c) 75

(e) 3

Mechanical Waves

• Are not capable of transmitting its energy through a vacuum (space)

• Require a medium in order to transport their energy from one location to another

Mechanical Waves

• Waves traveling through a solid medium can be either transverse waves or longitudinal waves

• Waves traveling through a fluid (such as a liquid or a gas) are always longitudinal waves