Waves

• Boat stuck in the middle of a pond• A toy boat is stuck in the middle of a pond. • How can Bob retrieve the boat without entering

the water?

• Boat stuck in the middle of a pond• A toy boat is stuck in the middle of a pond. • How can Bob retrieve the boat without entering

the water?

As the rock comes in contact with the water it exerts a force. In which direction is the force?What is the result of this force?

As the rock comes in contact with the water it exerts a force. In which direction is the force?What is the result of this force?

What happens to the water?Where does the water go?

• In order to move the boat forward, in which direction does there need to be a force?

• In order to move the boat forward, in which direction does there need to be a force?

• What is the source of the force?• In which direction is the force pushing on the boat?

• So what is a wave?• Any disturbance that transmits energy through

matter or empty space• It’s the vibration of a particle

• Wave Motion

• Transverse Wave

Crest

Trough

Wavelength λ

Amplitude

Transverse wave

Resting Point

• So what is a wave?• Any disturbance that transmits energy through

matter or empty space• It’s the vibration of a particle

• Wave Motion

• Transverse Wave

• Longitudinal Wave

Longitudinal Wave

Compressions

Rarefactions

Wavelength λ

How Waves Travel

Wavelength λ

Amplitude

Bob watches the waves as they move under the dock.

1,2,3He counts them as they pass.He counts 10 waves in 5 seconds.How often do the waves pass under the dock?What is the frequency of the waves?10 waves per 5 second or2 waves per second

1,2,3Now he counts 15 waves in 5 seconds.How often do the waves pass under the dock?What is the frequency of the waves?15 waves per 5 seconds or3 waves per second

1 second of time6 waves In 1 second

6 w/ 1 s

6 w/s = frequency

Frequency is the number of waves per second.

1 second of time4.5 waves In 1 second

4.5 w/ 1 s

4.5 w/s = frequency

Frequency is the number of waves per second.

1 second of time12 waves In 1 second

12w/ 1 s

12 w/s = frequency

What if the wavelength changes?

If decrease the wavelength, you increase frequency.

1 second of time4.5 waves In 1 second

4.5w/ 1 s

4.5 w/s = frequency

What if the wavelength changes?

If you increase the wavelength, you decrease the frequency

1,2,3What if the waves are moving faster?The waves are the same, they are just moving faster.

2 seconds of time12 waves In 2 second

6w/ 1 s

6 w/s = frequency

What if the wave speed changes?

Wave speed is frequency times wavelength

S = f · λ

How do waves move?Imagine a vibrating particle……

How do waves move?Imagine a vibrating particle……It collides with another particle

The energy from the first particle is passed to the second and the second moves.

What if the particles are spread out more, like in the air?

So how fast do waves travel?

The speed of sound is 343 m/s near room temperature.Chuck Yeager was the first man to fly faster than the speed of sound.He flew at 293 m/s (480 mi/hr) at 12,000m (7.5 miles) high.How did he fly faster?At 12,000 m the speed of sound is only 290 m/s.Why the difference?

Hydrogen (0°C) 1286Helium (0°C) 972Air (20°C) 343Air (0°C) 331Glycerol 1904Sea water 1533Water 1493Mercury 1450Methyl alcohol 1143Diamond 12000Pyrex glass 5640Iron 5130Aluminum 5100Brass 4700Copper 3560Gold 3240Lead 1322Rubber 1600

Sound• Longitudinal wave• Mechanical wave• Needs a medium to travel through• Pitch• A product of frequency• Determined by speed of the vibrations• Or the speed of the wave• Humans can hear from 20 Hz to 20,000

Hz

Sound• Pitch• A product of frequency• Determined by speed of the vibrations• Or the speed of the wave• Humans can hear from 20 Hz to 20,000

Hz• Sounds above 20,000 Hz are known

as ultrasound• Sounds below 20 Hz are known as

infrasound

• Loudness• A product of amplitude• How much energy is In the vibration

Sound• Pitch

• Humans can hear from 20 Hz to 20,000 Hz• Sounds above 20,000 Hz are known

as ultrasound• Sounds below 20 Hz are known as

infrasound

• Loudness• A product of amplitude• How much energy is In the vibration

Sound

• Loudness• A product of amplitude• How much energy is In the vibration

• Both pitch and loudness are affected by energy• Energy is needed to vibrate the object• Energy is needed for the wave to move

• Resonance• All objects have a natural frequency at

which they vibrate.

Sound

• Resonance• All objects have a natural frequency at

which they vibrate.• When an object vibrates at the same

frequency as a nearby vibrating object it is called resonance.

The EarPinna

Auditory canal

Ear Drum

Hammer, anvil, stirrup

Cochlea

Auditory nerve

Eustachian tube

Semicircular canals

Light• Electromagnetic wave• Part electric, part magnetic

• Electrons release extra energy as a photon• These photons vibrate as transverse

waves

What is light?• Wave theory• Light travels in waves• Is reflects off objects• It can pass through other light• Particles would bounce off each other

• It converts to other energy

• Particle theory• Light travels as particles

What is light?

• Particle theory• Light travels as particles• Shadows

• Particle / wave theory• Light is a particle with the properties of a

wave

Electromagnetic Radiation

• Light The energy produced by the vibrations of electrically charged particles

e−

• Light The energy produced by the vibrations of electrically charged particles

e−

e−

Photon of light

e−

e−

e−

e−

e−

e−

e−

e−

e−

e−

Radio

Radio

Radio

Microwave

Microwave

Microwave (Radar)

Infrared

Infrared

Visible Light

Ultraviolet

Ultraviolet

Xray

Gamma ray