Why are both electromagnetic and mechanical waves needed to make movies? Waves. transfer energy but do not carry medium with them.

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1 Why are both electromagnetic and mechanical waves needed to make movies? S8P4a. Identify the characteristics of electromagnetic and mechanical waves. Name: MEDIUM: any substance through which waves travel. A medium can be a solid, liquid, gas or plasma. Empty space (vacuum) is not a medium! Waves transfer energy but do not carry medium with them Date: Mechanical Waves that need a medium to travel. Cannot travel through empty space. Electromagnetic (EM) Waves that do not need a medium to travel; can travel through empty space. All the waves on the electromagnetic spectrum (below) can travel through empty space. Longitudinal a type of mechanical wave longitudinal waves move back and forth parallel to movement of energy. Sound and seismic are longitudinal, mechanical wave Surface surface waves are mechanical combination of longitudinal and transverse waves circular motion at the surface water was are an example Transverse are electromagnetic waves transverse waves move up and down perpendicular to movement of energy light, microwaves, UV light, Xrays etc. are all transverse waves

2 S8P4f. Diagram the parts of the wave and explain how the parts are affected by changes in amplitude and pitch. Diagram the parts of a wave including their properties for both longitudinal and transversal waves. Longitudinal Transverse S8P4f. Diagram the parts of the wave and explain how the parts are affected by changes in amplitude and pitch. What are the three properties of a wave that can be measured? 1. Amplitude The distance a wave moves away from the rest position. Amplitude is altitude or height. Higher amplitude = higher energy. Loudness/volume increasing the amplitude increases the volume.

3 2. Wavelength the distance between 2 corresponding points on a wave. For example, the distance between 2 crests or two troughs. When the wavelength goes up the frequency goes down. Shorter wavelength = higher frequency = higher energy. 3. Frequency The number of waves that pass a given point in a set amount of time. To frequency, count the number of crests or troughs you see in a given time period. Frequency is measured in Hertz (Hz). When the frequency goes up the wavelength must go down. Higher frequency = higher energy! Pitch: is how high or low the sound is. This is not the same as volume. Think music higher like a violin or lower like a bass. The higher the frequency the higher the pitch.

4 Wave Behaviors Reflection Reflection is the bouncing back of a wave. You see what is reflected. Law of Reflection: the angle of incidence is equal to the angle of reflection Diffraction Diffraction is the bending of a wave around a barrier or through an opening. Diffraction depends on the size of the barrier and the wavelength. Refraction Refraction is the bending of a wave as it moves from one medium to another. This is why rainbows occur and why a straw looks bent in a glass of water. Refraction depends on the wavelength of the wave. Interference Constructive Destructive In constructive interference (a) the crests or troughs overlap and create a larger wave. In destructive interference (b) a crest may overlap a trough and they would cancel out. SOUND What is sound? a mechanical wave that is longitudinal created by the vibrations of particles How do you detect sound? Outer Ear: collects sound and funnels to eardrum Middle Ear : Ear drum vibrates and 3 bones amplify sound Inner Ear: Cochlea transfers sound into nerve impulses to the brain

5 Speed of Sound: 345m/s in air at room temperature. The speed of sound depends on 2 things: 1)temperaturesound travels fastest through objects at warmer temperature because the particles are moving more quickly; and 2) the medium-sound travels fastest through solids then liquids then gases. It does so because the particles in a solid are closer together. Pitch and Frequency: the higher the frequency the higher the pitch Doppler Effect: The Doppler Effect is the apparent change in the frequency of a sound caused by the motion of either the listener or the source of the sound. Loudness and Amplitude: Increasing the amplitude of a wave increases the volume INTERACTIONS OF SOUND WAVES Reflection (Echo): An echo is a reflected sound wave Echolocation: The use of echoes to locate objects. Bats and dolphins use echolocation. Interference: causes sonic boom as waves overlap and create a high density compression Sonic boom: the sound that is created when an object moves faster than the speed of sound. Occurs because the object moves through a wave that has constructively interfered. Resonance: when one object s vibrations causes another to vibrate at the same frequency. This is why opera singers can crack glass

6 LIGHT Speed of Light: 900,000 faster than the speed of light. 300,000 km/s or 3,000,000,000 m/s which is why you see the lightening before hearing the thunder. Electromagnetic Spectrum: all the electromagnetic waves are listed on the electromagnetic spectrum (see page 1). The EM Spectrum is arranged according to wavelength/frequency. Radio waves (left) have the longest wavelength and lowest frequency and are the least harmful because they have the lowest energy. Gamma Rays have the shortest wavelength/highest frequency and are the most dangerous. Visible light is towards the middle of the EM spectrum and includes the colors of the rainbow (ROYGBIV). The colors are arranged from longest wavelength (red) to shortest (violet). Absorption: when the medium absorbs the light ; causes the beam of light to dim

7 Scattering: when light bounces of particles in the air; explains why the sky is blue Light and Color: Transparent-most of the light is transmitted or passes through (plastic wrap) Translucent-some of the light is transmitted (wax paper) Opaque-no light is transmitted (foil) How is color determined? Transparent/Translucent- color is determined by the amount of light that passes through. A 2 liter of ginger ale is green is transmitted. Opaque-color is determined by the color(s) that are reflected. For instance, a red object reflects red light only, a purple object reflects red and blue (colors that make purple); white objects reflect all 7 colors and black objects absorb all the color.