What are Waves? Waves are an important part of the Earth, and they’re not just in the water!

What exactly is a wave?  Definition: A wave is any disturbance that transmits energy through matter or space.  Waves move through matter but they do not move the matter itself Ocean waves Sound waves Light waves Radio waves Microwaves Earthquake seismic waves

So how are these waves different?  A wave travels through a medium (example: water, ground, air, etc.)  A vibration is one complete back and forth movement.  Mechanical waves need a medium. a medium. -These waves disturb matter. matter.  Electromagnetic waves do not need a medium. do not need a medium.

Types of Waves  Particles in transverse waves vibrate in an up and down motion perpendicular to the wave direction.  Particles in a longitudinal wave vibrate back and forth in the same direction that the wave travels. (Parallel to the wave direction)  At the boundary between two media transverse and longitudinal waves can combine to form surface waves.

Parts of a Wave Crest: the highest point (top) Trough: the lowest point (bottom)

Properties of Waves  Amplitude is the height of a wave. It is how much a particle in the medium is disturbed by the wave.  Wavelength is the distance between one point in a wave to the same point in the next wave.  The crest is the top of a wave  The trough is the bottom of a wave.

Longitudinal Waves (Also called Compressional Waves)  Compression is an area in a longitudinal wave where the particles are closer together.

Longitudinal Waves  Rarefaction is an area in a longitudinal wave in which the particles are spread further apart.  The amount of compression in a longitudinal (or compressional) wave is like the amplitude of a transverse wave

More Wave Properties  The wave speed is measured as distance divided by time (S = D/T). But it can also be calculated by multiplying wavelength by frequency. Wave speed = wavelength x frequency Wave speed = wavelength x frequency  Frequency is the number of waves that pass a given point in a certain amount of time. Frequency = speed/wavelength Frequency = speed/wavelength Frequency is measured in hertz Frequency is measured in hertz

More Wave Movement…  Reflection: when waves bounce off of something.  A reflected sound wave is called an echo.  Refraction: when a wave is bent at an angle and passes through a new medium.  Diffraction: when a wave is bent around a barrier or an opening.  Interference: When waves combine or overlap interference occurs.

More Wave Properties…  When the vibrations of one object cause another nearby to vibrate that is resonance.  Some musical instruments can use resonance to produce sound, like a marimba.

What are electromagnetic waves?  Electromagnetic waves do not require a medium to transfer energy (unlike mechanical waves)  These waves carry both electrical and magnetic fields. They carry the electrical field vertically and the magnetic field horizontally. They carry the electrical field vertically and the magnetic field horizontally.  The energy carried by electromagnetic waves is called electromagnetic radiation.  These waves travel at the speed of light.

The Electromagnetic Spectrum  The light we see is visible light.

 Radio waves – AM/FM Radio. Longest wavelengths Longest wavelengths  Microwaves – microwave oven  Infrared rays – used by heat lamps and night vision goggles  Visible light – the “colors” that we can see.  Ultraviolet rays – can cause skin cancer, insects use to locate nectar  X-rays – used to make images of bones.  Gamma rays – Used in cancer treatments (radiation therapy) shortest wavelengths, but carry the greatest amount of energy shortest wavelengths, but carry the greatest amount of energy

Wave Calculations Speed = Wavelength x Frequency Frequency = Speed/Wavelength Wavelength = Speed/Frequency Sample problem: The speed of a wave on a rope is 50 cm/second and the wavelength is 10 cm. What is the frequency?  Frequency = 50 cm/s / 10 cm  50 / 10 = 5 (5 per second) or 5 Hz

More sample problems  A wave has a wavelength of 5 mm and a frequency of 2 Hz. At what speed does the wave travel?  Answer: speed = wavelength x Frequency 5(mm) x 2 (Hz) = 10 mm per second 5(mm) x 2 (Hz) = 10 mm per second  The speed of a wave on a guitar string is 100 m/s and the frequency is 1000 Hz. What is the wavelength of the wave?  Answer: wavelength = speed/Frequency 100 (m/s) / 1000 (Hz) = 0.1 meter 100 (m/s) / 1000 (Hz) = 0.1 meter