Unit 2 Lesson 3 Sound Technology Copyright © Houghton Mifflin Harcourt Publishing Company

Hello Hello Hello How are echoes used? Unit 2 Lesson 3 Sound Technology Hello Hello Hello How are echoes used? Echolocation is the use of echoes to find food and other objects. Animals produce ultrasound, which are sound waves that have frequencies greater than 20,000 Hz, for echolocation. The frequencies of these ultrasonic waves are too high for humans to hear. The time it takes for ultrasound to bounce off an object and return to the animal tells the animal how far away the object is. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 3 Sound Technology How are echoes used? Though people cannot send out or hear ultrasound, people can still use echolocation in various technologies. Sonar is a system that uses echoes to determine the locations of objects or to communicate. Sonar is used to map out ocean floors, find fish, avoid icebergs, and help visually impaired people navigate on land. Copyright © Houghton Mifflin Harcourt Publishing Company

How are echoes used? How is sonar used to map the ocean floor? Unit 2 Lesson 3 Sound Technology How are echoes used? How is sonar used to map the ocean floor? Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 3 Sound Technology How are echoes used? Ultrasound procedures use high-frequency sounds to produce images of the inside of a person’s body. Ultrasound that has a frequency of 1 million to 10 million hertz can pass into a person’s body. Ultrasounds do not harm human cells, like x-rays do. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 3 Sound Technology How are echoes used? The sound waves reflect when they meet internal organs. The reflected waves create an image of whatever organ they bounce off of. Ultrasounds are used to check how a fetus is growing in a mother’s body. Copyright © Houghton Mifflin Harcourt Publishing Company

How do telephones transmit sound? Unit 2 Lesson 3 Sound Technology How do telephones transmit sound? Sound waves lose energy over time. Phones change sound waves into other types of signals that can be sent over long distances. These signals are then changed back into sound waves that can be heard. Copyright © Houghton Mifflin Harcourt Publishing Company

How do telephones transmit sound? Unit 2 Lesson 3 Sound Technology How do telephones transmit sound? All telephones change sound into electrical signals. Cordless phones change the electrical signal into radio waves that travel through air at the speed of light. The base picks up the radio waves and changes them back into electrical signals that are sent through wires. A computer sends these signals to the other phone, where they are changed back into sound waves. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 3 Sound Technology Hello, Operator People used to have to call telephone operators, who plugged wires into a switchboard to connect one phone to another. The invention of the rotary dial made it possible for people to call a number directly, replacing telephone operators. Cell phones use radio waves to send signals to phone towers. The towers transfer the signals to phone cables. Copyright © Houghton Mifflin Harcourt Publishing Company

Groovy How is sound recorded and played back? Unit 2 Lesson 3 Sound Technology Groovy How is sound recorded and played back? Sound is recorded to preserve sound information, such as interviews and music. Thomas Edison invented the phonograph, which could record and play back sound. Information in sound was recorded in the grooves of records. Now it is stored on CDs or in computer files. Copyright © Houghton Mifflin Harcourt Publishing Company

How is sound recorded and played back? Unit 2 Lesson 3 Sound Technology How is sound recorded and played back? A compact disc, or CD, is made of hard plastic. The information in sound waves is stored by pressing microscopic pits into the plastic. Light from a laser reflects off the shiny surface as the CD rotates. The detector changes the pattern into an electrical signal, which is then changed back into sound waves. Copyright © Houghton Mifflin Harcourt Publishing Company

How is sound recorded and played back? Unit 2 Lesson 3 Sound Technology How is sound recorded and played back? How does a laser read a CD? Copyright © Houghton Mifflin Harcourt Publishing Company

How is sound recorded and played back? Unit 2 Lesson 3 Sound Technology How is sound recorded and played back? Sound is also recorded as a digital file in a computer. Digital files, such as MP3 files, store large amounts of information. More sound files can be stored in a computer or an MP3 player than on a CD. Copyright © Houghton Mifflin Harcourt Publishing Company

How is sound recorded and played back? Unit 2 Lesson 3 Sound Technology How is sound recorded and played back? First, the original sound gets changed into an electrical signal. Then, it is stored as a digital file on a hard drive. The digital file is a series of 1s and 0s. Software reads the files and produces electrical signals that are sent to speakers. The speakers change the signal back into sound waves. Copyright © Houghton Mifflin Harcourt Publishing Company