Waves

Objectives Recognize that waves carry energy but not matter Define mechanical waves Distinguish between transverse and compressional waves. CLE 3202.2.1 Investigate the properties and behaviors of mechanical and electromagnetic waves.

The Nature of Waves Wave – is a repeating disturbance or movement that transfers energy through matter or space Molecules pass energy on to neighboring molecules. Waves carry energy without transporting matter

The Nature of Waves All waves are produced by something that vibrates Medium – a material through which a wave travels May be solid, liquid, gas or combination Sound waves – medium is air Ocean waves – medium is water

The Nature of Waves Not all waves need a medium to travel through. Example: Light & radio waves (space) Electromagnetic waves don’t need a medium (e.g. visible light)

Mechanical Waves Mechanical waves – waves that can travel only through matter 2 types: transverse and compressional

Transverse Waves Transverse waves – matter in the medium moves at right angles to the direction that the wave travels Example: water waves

B. Transverse Waves Transverse Waves medium moves perpendicular to the direction of wave motion

Water Waves

corresponds to the amount of energy carried by the wave B. Transverse Waves Wave Anatomy corresponds to the amount of energy carried by the wave wavelength crests amplitude nodes troughs

2. Mechanical waves need a matter medium to travel through. (sound, water, seismic) 3. Two basic types of waves: a. Transverse b. Compressional (longitudinal)

The Nature of Waves Compressional waves – matter in the medium moves in the same direction that the wave travels. Example: Sound waves Nearby air molecules pushed together by vibrations Travel through water and wood Particles pushed together and move apart Vibration of eardrum

Sound Waves

The Nature of Waves Combinations – not purely transverse or compressional; Example: water waves, seismic waves See Fig. 5 See Fig. 6 pg 330

Seismic Wave

Question 1 What is a wave? Answer Section Check 1 Question 1 What is a wave? Answer A wave is a repeating movement that transfers energy through matter or space.

Which is carried by a water wave? Section Check 1 Question 2 Which is carried by a water wave? A. a boat on the surface B. boat anchor submerged 50 m C. energy D. water molecules

Section Check 1 Answer The answer is C. Waves carry energy without transporting matter from place to place. FL: SC.A.2.4.6

Which type of wave does not need a medium? Section Check 1 Question 3 Which type of wave does not need a medium? A. electromagnetic B. mechanical C. ocean D. sound

Section Check 1 Answer The answer is A. Electromagnetic waves are made by vibrating electric charges and can travel through space where matter is not present.

How are sounds made? When somebody vibrates their vocal chords or slams a door, air particles are pushed together. This starts a sequence of compressions in the air that make a wave.

How are sounds made? The air particles pass the energy on to neighboring air particles. When the wave reaches your ear, it causes your eardrum to vibrate. Your inner ear sends signals to your brain, which your brain interprets as sounds.

Objectives Given a diagram, be able to identify the parts of a transverse and a compression wave Given an illustration, be able to identify the amplitude, frequency, and wavelength CLE 3202.2.1 Investigate the properties and behaviors of mechanical and electromagnetic waves.

Wave Properties Ways waves differ How much energy they carry How fast they travel

Wave Properties How they look Transverse waves have crests – the highest points, and troughs – the lowest points Compressional waves have dense regions called compressions and less dense regions called rarefactions

Crest vs Trough

Wave Properties Wavelength – the distance between one point in the wave and the nearest point just like it Frequency – how many wavelengths pass a fixed point each second

Wave Properties Expressed in hertz (Hz) As frequency increases, wavelength decreases The frequency of a wave equals the rate of vibration of the source that creates it

Wave Properties Speed of wave depends on properties of the medium it is traveling through Wave velocity describes how fast the wave moves forward. Velocity = wavelength X frequency

Wave Properties Light waves travel faster than sound waves Sound waves travel faster in liquids and solids than in gases Light waves travel faster in gases and empty space than in liquids and solids

Wave Properties Amplitude – a measure of the energy in a wave The more energy a wave carries, the greater its amplitude

Wave Properties Amplitude of compressional waves is related to how tightly the medium is pushed together at the compression

Wave Properties 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

Wave Properties Amplitude of transverse waves The distance from the crest or trough of a wave to the normal position of the medium Example: how high an ocean wave appears above the water level

Amplitude

In a thunderstorm, why do you see lightning before you hear the thunder? Light waves travel much faster than sound waves.

Thunder & Lightning

The Behavior of Waves 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

The Behavior of Waves 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

Incidence – Reflection w/Normal

The Behavior of Waves Refraction – the bending of a wave caused by a change in its speed as it moves from one medium to another

The Behavior of Waves 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

Refraction of Light in Water Light waves travel slower in water than in air. This causes light waves to change direction when they move from water to air or air to water. When light waves travel from air to water, they slow down and bend toward the normal.

Prism refracts the light twice -once when it enters the prism and again when it leaves the prism.

The Behavior of Waves Diffraction – an object caused a wave to change direction and bend around it If the obstacle is smaller than the wavelength, the wave diffracts a lot If the obstacle is larger than the wavelength, the wave does not diffract much

The Behavior of Waves The larger the obstacle is compared to the wavelength, the less the waves will diffract

Interference – the ability of two or more waves to combine and form a new wave

The Behavior of Waves Waves pass right through each other and continue in their original direction New wave exists only while the two original waves continue to overlap

The Behavior of Waves Constructive interference – waves add together Destructive interference – waves subtract from each other

The Behavior of 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

The Behavior of Waves Nodes – the places where two waves always cancel each other Resonance – the ability of an object to vibrate by absorbing energy at its natural frequency

Nodes

How do you think wave behaviors apply to music? Constructive interference causes sound waves to become louder; destructive interference causes sound waves to become more quiet. Standing waves create rich, even, constant tones in music.

Sonic Boom vs Boom Cone