Waves and Wave Characteristics

What is a wave? A wave is a disturbance or vibration that carries energy without carrying matter. Examples: – Ripples on the surface of a pond – sound in air – visible light – Seismic Waves (Shock Waves) – X rays – Radio Waves – infrared rays

Example: Ripples on the surface of a pond

Example: sound in air

Example: visible light

Example: Seismic Waves (Shock Waves)

Example: X-Rays

Example: Radio Waves

What is a wave? In physics, a wave is a traveling disturbance that travels through space or matter bringing energy from one place to another. energy It is important to remember that waves transfer energy, not matter

What is a wave? Traveling disturbance in water molecules

What is a wave? The energy (disturbance) travels, not the water

What is a wave? Have you ever "done the wave" as part of a large crowd at a football or baseball game? A group of people jumps up and sits back down, some nearby people see them and they jump up, some people further away follow suit and pretty soon you have a wave travelling around the stadium. The wave is the disturbance (people jumping up and sitting back down), and it travels around the stadium. However, none of the individual people the stadium are carried around with the wave as it travels - they all remain at their seats.

What is a wave? The energy (disturbance) travels, not the people:

What is a wave? Sound waves in air behave in much the same way. As the wave passes through, the particles of the air move back and forth but it is the disturbance which travels, not the individual air molecules.

What is a wave? Transverse waves on a string are another example. The string is displaced up and down as the wave travels from left to right, but the string itself does not experience any net motion

Mechanical Waves: Mechanical waves are waves that need a substance (medium) to travel through Examples: – Sound traveling through air or water – Seismic waves traveling through the Earth – Vibrations traveling through the table top

Electromagnetic Waves: Electromagnetic waves are waves that do not need a substance (medium) to travel through Examples: – Light traveling through space – Radio waves communicating with a space station – X rays

Transverse Waves: A wave that vibrates at a 90° angle to the direction of the wave.

Transverse Waves: A wave that vibrates at a 90° angle to the direction of the wave.

Transverse Waves: center line The center line of a transverse wave represents the position of the medium when it is undisturbed.

Parts of a wave: Crests and Troughs Crest – the part of a wave above the centerline Trough – the part of a wave below the centerline Trough Crest

Wave Characteristics: Wavelength Wavelength is the distance of one complete wave It is usually measured meters

Wave Characteristics: Wavelength Wavelength is the distance of one complete wave It can be measured crest to crest or trough to trough

Wave Characteristics: Amplitude Amplitude is how tall a crest is from the center line (or how deep it is from the centerline)

Wave Characteristics: Amplitude The higher the Amplitude of a wave, the more energy the wave has High Amplitude = High Energy Low Amplitude = Low Energy

Wave Characteristics: Frequency Frequency – the number of waves that go by in one second Frequency is measured in Hertz (Hz)

Wave Characteristics: Frequency

Animations: me/animations3/waves/Wave_Characteristics. html me/animations3/waves/Wave_Characteristics. html

Wave Characteristics: Period Period: time for an entire wave cycle to pass a given point the amount of time it takes for one wave to pass by Period is measured in seconds (s)

Wave Characteristics: Period

me/notes/waves/PeriodAmplitude.htm me/notes/waves/PeriodAmplitude.htm

Wave Characteristics: f = frequency units: Hz (Hertz) λ = wavelength units: m (meters) v = speed units: m/s v = f ∙ λf = v ÷ λ λ = v ÷ f

A wave has a frequency of 88Hz and a wavelength of 4 meters. What is its speed in m/s? G iven U nknown E quation S olution f = 88 Hz λ = 4 m v = ? v = f ● λ v = 88 ● 4 v = 352 m/s Scientific Units

A wave has a speed of 450 m/s and a wavelength of 0.2 meters. What is its frequency in Hz? G iven U nknown E quation S olution v = 450 m/s λ = 0.2 m f = ? f = v ÷ λ f = 450 ÷ 0.2 f = 2250 Hz Scientific Units

A wave has a speed of 120 m/s and a frequency of 600 Hz. What is its wavelength in meters? G iven U nknown E quation S olution v = 120 m/s f = 600 Hz λ = ? λ = v ÷ f λ = 120 ÷ 600 λ = 0.2 m Scientific Units

Wave Characteristics: f = frequency units: Hz (Hertz) T = period units: s (seconds) T = # of WavesT = 1 ÷ f time

5 ocean waves pass by a boat in 25 seconds. What is the period of the waves? G iven U nknown E quation S olution # = 5 t = 25 s T = ? T = # waves time T = # ÷ t T = 5 ÷ 25 T = 0.2 s Scientific Units

The frequency of a sound wave is 20 Hz. What is the period of the waves? G iven U nknown E quation S olution f = 20 Hz T = ? T = 1/f T = 1 ÷ f T = 1 ÷ 20 T = 0.05 s Scientific Units