Chapter 10

Waves

Chapter 1o Section 1

The Nature of Waves

What is a wave?

• Wave – a repeating disturbance or movement that transfers energy through matter or space

What is a wave?

• Wave – a repeating disturbance or movement that transfers energy through matter or space1. Molecules pass energy on to neighboring

molecules

What is a wave?

• Wave – a repeating disturbance or movement that transfers energy through matter or space1. Molecules pass energy on to neighboring

molecules2. Waves carry energy not matter.

What is a wave?

• Wave – a repeating disturbance or movement that transfers energy through matter or space1. Molecules pass energy on to neighboring

molecules2. Waves carry energy not matter.3. All waves are produced by something that

vibrates. (anything that moves up and down or back and forth)

A Medium

• A medium is a material through which a wave travels.– can be solid, liquid, or gas– not all waves need a medium to travel through• Example – Light waves or Radio Waves

Mechanical Waves

• A mechanical wave is a wave that can travel only through matter. (solid, liquid, gas)– Example: Sound wave

• Question: Is theresound in space?

Is their sound in space?

Mechanical Waves

• A mechanical wave is a wave that can travel only through matter. (solid, liquid, gas)

– Transverse waves vs. Compressional waves

Transverse waves

• Matter in a medium moves back and forth at right angles to the direction that the wave travels.

• AKA an S-Wave

• Ex. Water waves

Compressional Waves

• Matter in the medium moves in the same direction that the wave travels.

• AKA P-waves• Ex. Sound

waves

Combination of Waves

• Some waves are not purely transverse or compressional but instead will have a combination of both types of waves.

• Ex. Seismic waves

• http://video.nationalgeographic.com/video/player/environment/environment-natural-disasters/tsunamis/tsunami-101.html

• http://video.nationalgeographic.com/video/player/environment/environment-natural-disasters/earthquakes/earthquake-101.html

Wave Properties

Chapter 10 Section 2

Waves can differ in…

1. How much energy they carry2. How fast they travel 3. How they look

Parts of a Wave

• Transverse waves– Crests – the high points– Troughs – the lowest points

Parts of a Wave

• Compression waves– compressions – the dense regions– rarefactions – the less dense regions

What is Wavelength?

• The distance between one point in the wave and the nearest point just like it.

Frequency…• Frequency is how many wavelengths pass a fixed point

each second1. # expressed in hertz (Hz)2. As frequency

increases, wavelength decreases

3. The frequency of a wave equals the rate of vibration of the source that creates it.

Frequency

• A period of a wave is the amount of time it takes one wavelength to pass a point.

• As the frequency of a wave increases, the period decreases.

• Period has units of seconds.

Wave Speed

• Wave velocity, or v, describes how fast the wave moves forward.1. Velocity = wavelength x frequency

or v = λ x f2. light waves travel faster than sound waves (ex.

thunder and lightning, baseball bat)3. Sound waves travel faster in liquids and solids

than in gas.4. Light waves travel faster in gases and empty

space than in liquids and solids.

Amplitude

• Amplitude is the measure of the energy in a wave.

• Amplitude of a compressional wave is related to how tightly the medium is pushed together at the compression– the denser the compressions, the larger the

amplitude is and the more energy the wave carries

– the less dense the rarefactions, the larger the amplitude and the more energy the wave carries

The Behavior of Waves

Chapter 10 Section 3

Reflection

• Reflection occurs when a wave strikes an object and bounces off of it.

Reflection

• Reflection occurs when a wave strikes an object and bounces off of it.– All types of waves can be reflected– The angle of incidence of a wave is always equal

to the angle of reflection.

Reflection• Reflection occurs when a wave

strikes an object and bounces off of it.– All types of waves can be reflected– The angle of incidence of a wave

is always equal to the angle of reflection.• Normal – an imaginary line perpendicular to a reflective

surface• Angle of incidence – the angle formed by the wave striking

the surface and the normal• Angle of reflection – the angle formed by the reflected wave

and the normal

Refraction• Refraction – the bending of a wave caused by

a change in its speed as it moves from one medium to another

Refraction• Refraction – the bending of a wave caused by a

change in its speed as it moves from one medium to another– The greater the change in speed is, the more the wave

bends– When a wave passes

into a material that slows it down, the wave is bent toward the normal

– When a wave passes into a material that speeds it up, the wave is bent away from the normal.

• Diffraction – an object causes a wave to change direction and bend around it

• Diffraction – an object causes a wave to change direction and bend around it

Diffraction

• Diffraction – an object causes a wave to change direction and bend around it– If the object is smaller than the wavelength, the

wave diffracts a lot.– If the obstacle is much larger than the

wavelength, the wave does not diffract much– The larger the obstacle is compared to the

wavelength, the less the waves will diffract.

Diffraction and Radio Waves

• AM radio waves have longer wavelengths than FM radio waves.– Because of these longer wavelengths, AM radio waves diffract around

obstacles like buildings and mountains.– AM radio reception is often better than FM reception around these

large structures.

Interference

• The ability of two or more waves to combine and form a new wave.

Interference

• The ability of two or more waves to combine and form a new wave.1. Waves pass right

through each other and continue in their original direction.

Interference

• The ability of two or more waves to combine and form a new wave.1. Waves pass right through each other and continue in

their original direction.2. New wave exists only while the two original waves

continue to overlap

Interference

• The ability of two or more waves to combine and form a new wave.1. Waves pass right through each other and continue in

their original direction.2. New wave exists only while the two original waves

continue to overlap3. Constructive interference – waves add together4. Destructive interference – waves subtract from each

other

Standing Waves

• Standing waves – a wave pattern that stays in one place

Standing Waves

• Standing waves – a wave pattern that stays in one place– Form when waves of equal wavelength and amplitude that

are traveling in opposite directions continuously interfere with each other.

– Nodes form at the places where two waves always cancel each other.

Resonance

• Resonance – the ability of an object to vibrate by absorbing energy at its natural frequency.