Waves Wave: a rhythmic disturbance that transfers energy through matter or space. Carries energy without carrying matter from place to place.

Waves can be either Electromagnetic or Mechanical. Classifying Waves Waves can be either Electromagnetic or Mechanical. Electromagnetic Waves: waves capable of transferring energy through a vacuum. Ex. Light waves Mechanical Waves: waves that can only travel through a medium. Medium: matter through which a wave travels through; can be solid, liquid, or gas. Ex. Sound waves, water waves I always like to say with this picture that astronauts can take selfies in outer space, due to the ability of electromagnetic waves to travel through a vacuum, but they can’t talk on the phone, due to the lack of a medium for sound waves to travel through.

Waves can be either Transverse or Longitudinal. Classifying Waves Waves can be either Transverse or Longitudinal. Transverse: matter in the medium moves back and forth at right angles to the direction that the wave is traveling. Particle motion is perpendicular to wave motion. Ex. Electromagnetic waves, vibrations in string instruments, ripples of surface of water. Longitudinal: (aka compressional waves) matter in the medium moves back and forth in the same direction that the wave is traveling. Particle motion is parallel to wave motion. Ex. Sound waves, ultrasounds, waves made with a slinky. Transverse wave demo: Use a rope or jump rope by shaking the end of the rope while holding on the ground (flashback to elementary school days on the playground!) Longitudinal wave demo: Use a slinky by holding both sides somewhat stretched out and straight. Apply force to push one side to show how matter moves in the same direction as the wave travelling through the slinky.

Labeling Parts of Waves In transverse waves… Crest: (aka peak) highest points of a transverse wave. Trough: lowest points of a transverse wave. Normal resting position of wave

Labeling Parts of Waves In longitudinal waves… Compression: where particles are pushed together in a longitudinal wave. Rarefaction: where particles are spread apart in a longitudinal wave. Compression Rarefaction

The amount of compression in the wave Measuring Waves Amplitude: the amount of energy carried by a wave. Transverse Waves The height of the wave Longitudinal Waves The amount of compression in the wave

Measuring Waves Wavelength: (𝞴) the distance between one point on a wave and the nearest point just like it. Measured in m Longitudinal Waves Compression to compression, or rarefaction to rarefaction Transverse Waves Crest to crest, or trough to trough

Frequency and period have an inverse relationship. Measuring Waves Period: (T) the amount of time it takes one wavelength to pass a point. Measured in s Frequency: (𝒇) the number of waves that pass a given point in one second. Measure in Hertz (Hz) I Hertz = 1/s or s-1 I always tell students to remember that if you have one, you can always find the other, because of this relationship! T = 1 𝒇 Frequency and period have an inverse relationship. 𝒇 = 1 T

Measuring Waves Frequency and wavelength also have an inverse relationship. The higher the frequency, the shorter the wavelength. The lower the frequency, the longer the wavelength.

Measuring Waves Wave speed: (v) how fast the wave travels. Measured in m/s Speed is dependent on the type of wave and properties of the medium the wave is traveling through. Mechanical waves (like sound): must travel through particles, therefore travel fastest through solids, then liquids, then gases, due to the closeness of the particles. Also travel faster through warmer mediums, because particles collide more. Electromagnetic waves (like light): do not need a medium, therefore travel fastest through a vacuum, and slowest through solids. Each time electromagnetic waves come up, I remind students we will spend an entire concept on them for Concept 3!

To calculate wave speed: Measuring Waves To calculate wave speed: v = 𝞴𝒇 v = velocity Measured in m/s 𝞴 = wavelength Measured in m 𝒇 = frequency Measured in Hz Example #1: What is the speed of a wave with a wavelength of 2 m and a frequency of 3 Hz? λ = 2 m f = 3 Hz v = ? v = (2)(3) v = 6 m/s v = 𝞴𝒇

Example #2 A wave is traveling at a speed of 12 m/s and its wavelength is 3 m. Calculate the wave’s frequency and period. v = 12 m/s λ = 3 m f = ? T = ? f = 12 3 T = 1 4 f = 4 Hz T = 0.25 s v = λ f λ λ f = v λ T = 1 𝒇

Practice Time A tuning fork has a frequency of 280 Hz and the wavelength of the sound produced is 1.5 m. Calculate the velocity of the wave. A wave is moving toward shore with a velocity of 4 m/s. If its period is 0.4 s, what is its wavelength? Answer: v = 420 m/s I have students work these out in their notes and I walk around and help them as they work. Then we go over the answers all together. I especially encourage CP students that if they don’t know what to do, they at least need to set up the problem (labeling values that they know and writing the appropriate equation.) They should NEVER leave a problem blank! #2 they may need the hint that they may want to find frequency first, then wavelength! (Or they can throwback to our traditional s = d/t calculations!) Answer: 𝞴 = 1.6 m