Waves

What is a Waves?  A wave is a disturbance that transfers energy through matter or space. w When waves move through matter, we call the matter a medium. A medium can be solid, liquid, or gas. wTransverse waves can move through empty space without a medium. wWhen energy waves move through a medium, the medium stays in the same place. wIn the ocean, when a wave passes, the water molecules move only in small circles!

Types of Waves : Transverse wA wave in which the medium moves at right angles to the direction of the wave is a transverse wave. wOcean waves and light waves are transverse.

Parts of a Transverse Wave The crest is the highest point of a transverse wave, and the trough is its lowest point. One wavelength includes one complete crest plus one complete trough The amplitude of a transverse wave in the distance from the normal to a crest or from the normal to a trough. The more energy a wave has, the greater the amplitude

Types of waves: longitudinal wA longitudinal wave has the medium move parallel to the direction of the wave. wUnlike transverse waves which can travel in empty space a longitudinal waves must have a medium to travel through. wSound travels in longitudinal waves. wBecause sound is a longitudinal wave, sound will not travel in empty space.

Parts of a Longitudinal Wave The part of a longitudinal wave where the particles of the medium are close together is a compression. The part of a longitudinal wave where the particles of the medium are far apart is a rarefaction. One wavelength includes one complete compression plus one complete rarefaction.

Wave properties wWhen you talk about a “big wave,” you are describing the wave’s amplitude. wIf you describe how many waves pass in a given time, you are describing the wave’s frequency. wFor a transverse wave, the distance from crest to crest or trough to trough is a wavelength. wFor a longitudinal wave, a wavelength is the distance between compressions or between rarefactions.It is measured in meters. amplitude wavelength rarefaction compression wavelength

Wave amplitude wIf you are observing transverse waves, the amplitude is the vertical distance from the line of origin and the crest OR the line of origin and the trough. wAs you increase a wave’s energy, its amplitude also increases. Low amplitude High amplitude

Wave frequency wThe frequency of a wave is the number of waves that pass a point in a given time. Low frequency wThe unit for frequency is the Hertz, which means waves per second. High frequency

Wave speed wWave speed measures how fast a wave is moving toward you. wWave speed = frequency x wavelength wThe unit used to measure wave speed is meters per second.

Math Problems with Waves Speed = frequency x wavelength Speed Freq. wavelength

Complete the practice problems

Wave interactions: Energy and change wWhen a wave interacts with another wave or with an object, the amount of energy in the wave changes. wThe change in energy affects the wave’s properties. wWave properties include, its amplitude, speed, frequency or wavelength which may change. wWave interactions affect all wave types. wOther changes that may happen are a change in wave direction, or the wave may break apart and then re-form.

Wave interactions: wave reflection wReflection happens when a wave bounces off of a surface. wThe angle of the incoming (incident) wave equals the angle of the outgoing (reflected) wave. incident wave Angle of incidence Normal reflected wave Angle of reflection This is called the Law of Reflection

Wave Interactions Refraction Waves can change speed when they pass from one medium to another. Sounds travel fastest in solids and slower in air. Sound is slowest in mediums like air and does not travel in a vacuum. Light travels fastest in a vacuum, gas, and even slower through a liquid, and even slowest through a solid like glass. Refraction is the bending of a wave as it passes through a medium.

Wave interactions: refraction Pt2

Wave interactions: diffraction wThe bending of a wave as it contacts the edge of a barrier is called diffraction. wWhen waves are diffracted at the edge of a barrier, their wavelengths and frequencies do not change. outgoing wave crests Incoming wave crests Diffraction allows you to hear around corners and diffraction glasses split light into colors of the rainbow

Wave interactions: interference wThe effect of two or more interacting waves is interference. wThere are 2 types of interference constructive and destructive. wWhen two crests meet, the result is a larger wave. This is constructive interference. A tidal wave such as a tsunami is caused by constructive interference ! ! ! Constructive Interference

When a crest and a trough meet, the result is a smaller wave. This is destructive interference. In some auditoriums destructive interference makes it difficult to hear what is on stage. Destructive Interference