6th Grade: Sound and Light (Module J) Physical Science for Children All About Waves https://www.youtube.com/watch?v=k8-AeEByU4c Unit 1: Introduction to Waves Lesson 1: Waves Lesson 2: Properties of Waves

What are waves? Unit 1 Lesson 1 Waves Waves: disturbances that transfer energy from one place to another. Some waves, such as ocean waves, transfer energy through a medium (material wave travels through) Some waves, such as light waves, can transfer energy without a medium Ex: water sound waves Copyright © Houghton Mifflin Harcourt Publishing Company 2

Highest point – crest Lowest point – trough Draw one and label it! Unit 1 Lesson 1 Waves Highest point – crest Lowest point – trough Draw one and label it! Do #7 and #8 on page 7 Waves transferring energy animation - http://www.classzone.com/books/earth_science/terc/content/visualizations/es1604/es1604page01.cfm Copyright © Houghton Mifflin Harcourt Publishing Company 3

Waves transfer energy in different ways Unit 1 Lesson 1 Waves Longitudinal wave – particles vibrate in the SAME DIRECTION (parallel) as the wave travels Ex. Sound waves -Compressions - when the coils (or particles) are close together -Rarefactions - when the coils are far apart. Get out the slinky! Copyright © Houghton Mifflin Harcourt Publishing Company 4

Unit 1 Lesson 1 Waves 2. Transverse wave – particles move perpendicular to the direction the wave travels ex. Water waves -Wave moves up and down Copyright © Houghton Mifflin Harcourt Publishing Company 5

Earthquakes send out both types of waves. Primary waves (P waves) are longitudinal waves. They always arrive first. Secondary waves (S waves) are transverse waves. They always arrive second. They can combine to form a surface wave, like ripples on a pond. Unit 1 Lesson 1 Waves Do 10, 11, 12 & 13 on p. 8 & 9 Copyright © Houghton Mifflin Harcourt Publishing Company 7

Types of Waves Unit 1 Lesson 1 Waves Mechanical waves - Waves that require a medium (like water waves) Can be longitudinal or transverse Some can travel through more than one medium ex: sound waves can move through air, water, and a solid wall. Mechanical waves can’t travel without a medium. Copyright © Houghton Mifflin Harcourt Publishing Company 8

Types of Waves, con’t Unit 1 Lesson 1 Waves Electromagnetic wave - a disturbance in electric and magnetic fields Also called EM waves All are transverse waves Ex: Sunlight (visible light and UV light), radio waves, microwaves, and X-rays. In empty space, all EM waves travel at the same speed – the speed of light. Do page 11 Copyright © Houghton Mifflin Harcourt Publishing Company 10

The size of the wavelength determines the wave (the next lesson!)

Lesson 2: Properties of Waves Physical Science for Children All About Waves https://www.youtube.com/watch?v=k8-AeEByU4c

Describing waves Read and do page 18 Amplitude - measure of how far the particles in the medium move away from their normal rest position Wavelength - distance from any point on a wave to an identical point on the next wave -ex. From crest to crest, or trough to trough - Length of one cycle, or repetition

What is the wavelength of this wave? What is the wave’s amplitude? Unit 1 Lesson 2 Properties of Waves What is the wavelength of this wave? What is the wave’s amplitude? Copyright © Houghton Mifflin Harcourt Publishing Company 14

Describing waves, con’t. Wave period - time required for one wavelength to pass a given point Frequency - how many cycles occur in an amount of time, (usually 1 second) Measured in hertz (Hz) – one cycle per second Period and frequency are the INVERSE of each other Do amplitude and frequency animation - http://www.bbc.co.uk/schools/gcsebitesize/science/aqa_pre_2011/radiation/anintroductiontowavesrev2.shtml Short recap video w/quiz (only one question works)- http://www.bbc.co.uk/bitesize/standard/physics/telecommunications/communication_using_waves/activity/ Read, analyze and do page 19 Copyright © Houghton Mifflin Harcourt Publishing Company 15

Some waves carry more energy than others. mechanical wave: How much energy can a wave carry? Unit 1 Lesson 2 Properties of Waves Some waves carry more energy than others. mechanical wave: greater amplitude = more energy *for a sound wave, greater amplitude is a LOUDER sound Read page 20 Copyright © Houghton Mifflin Harcourt Publishing Company 16

electromagnetic (EM) waves: greater frequency = more energy How much energy can a wave carry? Con’t. Unit 1 Lesson 2 Properties of Waves electromagnetic (EM) waves: greater frequency = more energy Read page 20 Copyright © Houghton Mifflin Harcourt Publishing Company 17

As a wave travels through a medium, energy gets lost to the medium Higher-frequency waves lose energy more readily than lower-frequency waves lose energy. Ex: when you stand far from a concert, you might hear only the low-frequency (bass) sounds. Unit 1 Lesson 2 Properties of Waves Copyright © Houghton Mifflin Harcourt Publishing Company 19

Many waves spread out in circles or spheres, called wavefronts. Unit 1 Lesson 2 Properties of Waves Many waves spread out in circles or spheres, called wavefronts. As the circle expands, there is less energy available on the wavefront. Read & do page 21 Copyright © Houghton Mifflin Harcourt Publishing Company 20

What determines the speed of a wave? Unit 1 Lesson 2 Properties of Waves Wave speed, or the speed at which waves travel, depends on the properties of the medium. Waves travel faster in liquids than gas and faster in solids than liquids BUT more slowly in a denser medium OF THE SAME STATE OF MATTER. Tracking earthquake waves Copyright © Houghton Mifflin Harcourt Publishing Company 21

Q: Would a wave travel faster in air or water? A: Water Q: would a wave travel faster through a table or through water? A: a table Q: would a wave travel faster through a more dense solid (like metal) or a less dense solid (like wood)? A: A less dense solid (wood) Q: Would a wave travel faster through a more dense liquid like oil, or a less dense liquid like water? A: a less dense liquid like water

Speed of a wave, con’t Unit 1 Lesson 2 Properties of Waves In gases, wave speed is higher at higher temperatures. All electromagnetic waves travel at the same speed in empty space – the SPEED OF LIGHT Travel more slowly through a denser medium Ex: air to water Copyright © Houghton Mifflin Harcourt Publishing Company 23

How do we CALCULATE speed? Unit 1 Lesson 2 Properties of Waves Speed is distance divided by time. For a wave, distance = wavelength Time = wave period So… Wave speed = wavelength wave period Remember that frequency and wave period are inverses of each other, so we can rewrite it like this: Wave speed = frequency x wavelength Or Wavelength = wave speed frequency Read & do page 23 Copyright © Houghton Mifflin Harcourt Publishing Company 24

How can we describe a wave? Unit 1 Lesson 2 Properties of Waves How can we describe a wave? What is the wavelength of this wave? What is the wave’s amplitude? – Draw this in your notes! Copyright © Houghton Mifflin Harcourt Publishing Company 25