What is a wave?  A wave is a disturbance that carries energy through matter or space.  What type of wave examples can you think of?

Wave examples

Wave travel  Most waves require matter in order to travel.  The matter a wave travels through is called a medium.  For example, waves in an ocean travel through water. Water is the matter and medium.  Another example would be sound. Sound requires a medium, which is the air around us.  Waves that require a medium are called mechanical waves.

Not all waves require a medium  Electromagnetic waves do not require a medium.  They can travel through empty space.  For example, light waves travel from the sun to the earth through empty space.  Other examples would be radio waves, x-rays, and gamma rays.

Electromagnetic waves

Energy and Waves  WAVES TRANSFER ENERGY!  Energy is the ability to exert force over a distance and that is what waves do.  For example water waves can push a surfer along or a huge wave, like a tsunami, can carry trees and even houses with it.  So the bigger the wave, the more energy it carries.  Furthermore, energy in waves may spread out as it travels.  If you drop a rock into a pond it creates waves. The waves right around where the rock was dropped are the biggest. As they travel, the spread out, so energy spreads out.

Ripple

Tuning forks  Most waves are caused by vibrations.  For example, if you strike a tuning fork, the fork vibrates. The vibrations cause waves in the air.

Tuning Forks

Types of Waves  Particles in a medium (type of matter) can vibrate either up and down or back and forth.  Waves are classified according to the direction in which the particles in the medium move.  A transverse wave is a wave in which the wave motion is perpendicular to the particle motion. (They look like an ocean wave)  A longitudinal wave is a wave in which the wave motion is parallel to the particle motion. (They look like a slinky)

Transverse waves

Longitudinal (compressional) waves

Transverse waves  The crest is the high point of the transverse wave and the trough is the low point of the wave.  The wavelength is the distance from crest to crest or trough to trough.  The amplitude is the distance from the crest to the trough.

Longitudinal or compressional waves  The crowded areas of the wave are called compression and the stretched out part of the wave is called rarefaction.  The wavelength in a longitudinal wave is the distance between two compressions or between two rarefactions.

Longitudinal wave

Sound waves are longitudinal

Energy, frequency, and amplitude  The amplitude and wavelength tell you about energy.  Larger amplitude waves carry more energy  The shorter the wavelength of a wave, the higher the energy

Energy, frequency, and amplitude  Wave frequency is the number of cycles or vibrations per unit of time (the number of waves produced during a given time period.  Higher frequency waves carry more energy

Wave speeds and mediums  The speed of a wave depends on the medium (matter) it is traveling through. For example, when you talk to produce sound waves in the air around you. Sound travels at 340 m/s through the air. However, that same sound wave will travel 3 to 4 times as fast in water (1490 m/s). Sound waves travel even faster through solids. A sound wave will travel 15 to 20 times faster through rock or metal (Iron 5000 m/s) than through the air. Why?

Wave speed and mediums  The Kinetic theory is the answer. The arrangement of particles in a medium determines the speed. The closer the particles are packed together, the easier it is for one particle to bump into another and transfer the energy.  Gas particles are more spread out than liquid molecules. Liquid molecules are more spread out than gas.

Wave speed and mediums tmlhttp://faraday.physics.utoronto.ca/IYearLab/Intros/StandingWaves/Flash/long_wave.h tml.

The Doppler Effect  It is an observed change in the frequency of a wave when the source or observer is moving.  As the ambulance approached the frequency of the wave changes. It increases. You hear a high pitch sound because of the high frequency.  As the ambulance moves away the wave frequency changes. It decreases. You hear a low pitch sound because the frequency has is lower.

The Doppler Effect  pscale.utoron to.ca/GeneralI nterest/Harris on/Flash/Clas sMechanics/D opplerWaveFr onts/Doppler WaveFronts.h tml. pscale.utoron to.ca/GeneralI nterest/Harris on/Flash/Clas sMechanics/D opplerWaveFr onts/Doppler WaveFronts.h tml

Reflection  When waves meet a surface or a boundary, the waves bounce back. This is called reflection.  It is similar to a basketball bouncing off a back board.  Have you ever used a shiny watch to reflect light in someone’s eye?

Reflection  The reflection of sound waves can result in an echo.

Diffraction  When a wave passes the edge of an object or passes through an opening, the wave bends. This is called diffraction.  The sound we make in the classroom passes through the door and spreads out, creating a new sound wave in the hall.  The waves also bend around objects. This is why shadows don’t have sharp edges.

Refraction  The bending of waves as they pass from one medium into another is called refraction.  Let’s look at a utensil in a cup of water.  Each time waves enter a new medium they bend slightly because they change speeds.

Refraction  son/Flash/Waves/Refraction/Refraction.html. son/Flash/Waves/Refraction/Refraction.html  n/Flash/Optics/Refraction/Refraction.html. n/Flash/Optics/Refraction/Refraction.html  p?sim=Generator. p?sim=Generator

Refraction

The electromagnetic spectrum  The electromagnetic spectrum consists of waves at all possible energies, frequencies, and wavelengths.  Electromagnetic waves do not require a medium!  Visible light is part of the electromagnetic spectrum. Your eyes can detect these waves. However, they are just a small part, 400 to 700 nm.  Electromagnetic waves in order from the least amount of energy to the greatest amount of energy are radiowaves, microwaves (not just microwave ovens, but cell phones), infrared rays (special cameras are used to image temperature), visible light, UV light (Ozone layer protects us from these waves), X rays (we use these to see bones), and gamma rays (they are produced in nuclear reactions.

The electromagnetic spectrum The energy of electromagnetic waves depends on frequency. The higher the frequency the higher the energy. The lower the frequency, the lower the energy.

Electromagnetic spectrum