Chapter 20 The Energy of Waves
Section 1: The Nature of Waves • Student objectives • Describe how waves transfer energy without transferring matter. • Distinguish between waves that require a medium and waves that do not. • Explain the difference between transverse and longitudinal waves.
Vocabulary • Please add the following words to your SNB glossary • Waves • Medium • Transverse waves • Longitudinal waves
Light waves from the sun • Water waves in the ocean
Radio waves transmitted to the radio • Sound waves from the radio
Sounds waves from • The telephone ringing • And the voices on the phone
What do all waves have in common? • All waves are disturbances that transmit energy. • Energy can be carried away from its source by a wave. • As a wave travels, it does work on everything in its path. • The material through which the wave travels does not move with the energy
Remember when we talked about Light Energy Sound Energy • Is produced by the vibrations of electrically charged particles. Light vibrations cause energy to be transmitted (in waves). • Is caused by an object’s vibrations which transmits energy through the air around it (in waves)
But what’s the difference? • Most waves transfer energy by the vibrations of particles in a MEDIUM. • A medium is a substance through which a wave can travel. A medium can be a solid, liquid, or gas. • Sound waves NEED a medium. • Other wave that need a medium are ocean waves and earthquakes. • WAVES THAT NEED A MEDIUM ARE CALLED MECHANICAL WAVES.
Light waves are electromagnetic waves, which do not need a medium. Light can travel through the vacuum of space. SOUND CAN’T! • Misconception ALERT! • You may believe that sounds can be heard in a vacuum (like outer space). In many sci-fi movies, explosions and other sounds are heard in outer space. THIS IS SCIENTIFICALLY INACCURATE!
Energy transfer without a medium • Some waves can transfer energy without going through a medium: • Visible light, microwaves, TV and radio signals, and X rays. • WAVES THAT DO NOT NEED A MEDIUM ARE ELECTROMAGNETIC WAVES
WERE YOU PAYING ATTENTION? • How do electromagnetic waves differ from mechanical waves? • Electromagnetic waves do not require a medium.
Cup-and-string phone • Punch a small hole in the bottom of your cup. • Push the ends of a long piece of string through the bottoms of each cup. • Tie paper clips to the ends of the strings inside the cups • Have a partner take one cup and you take the other. • Move away from each other until the string is tight. • To talk, hold the rim of the cup around your mouth and speak clearly. To listen, hold the rim of the cup to your ear. • How does the cup-and-string phone transmit sound waves?
Answers to Ch.1 Sec.4 pg.27 1)Sample answers: • Volume is the amount of space taken up by matter. • Density is the amount of matter in a given volume. • Mass is the amount of matter an object contains. 2) C 3) Sample answer: Mass and density are related because in order to calculate density, the mass and volume of an object must be known. Density tells how much mass is in a certain volume. 4) The normal body temperature is 98.6 °F and 37°C. 5)1100÷0.5 = 2200 6) You would see eye protection, clothing protection, hand safety, and chemical protection because acid is corrosive and will cause severe burns if it come in contact with eyes, skin, or clothing.
Fun Fact: • Light travels 300,000,000 m/s. • 1 second = 1,000,000,000 nano seconds • This piece of string is how far light can travel in 1 nanosecond!!! • This piece of string is 30 cm long
Types of Waves • Particles in Transverse waves vibrate in an up-and-down motion. • The particles in this kind of wave move perpendicularly to the direction the wave is going. • CREST- the highest point of a transverse wave. • Trough- the lowest point between each crest of a transverse wave • **Although electromagnetic waves do not travel by vibrating particles in a medium, all electromagnetic waves are considered transverse waves.
In longitudinal waves, the particles of the medium vibrate back and forth along the path that the waves moves. • Compression- a part of a longitudinal wave where the particles are crowded together • Rarefactions- a part of a longitudinal wave where the particles are spread apart • Sound waves are examples of longitudinal waves. • Sound waves travel by compression and rarefactions of air particles. • Now, turn to page 578 and draw and label figure 6 into your SNB
Were you paying attention? • What kind of wave is a sound wave? • A sound wave is a longitudinal wave.
POP Quiz!!! • Clear off your desk • Take out a sheet of paper • Number 1-5 • Label your paper with your name and Chapter 20 section 1 Pop Quiz
5. In a _________, the particles vibrate back and forth along the path that the waves moves.
3. In a _____________, the particles move perpendicularly (up and down) to the direction that the wave travels.
True or False • 1. Light waves are mechanical waves because they must travel through a medium.
True or False • 2.In space, no one can hear an explosion.
How’s that Sound? • With this lab you’ll find out if sound travels better through a gas, a liquid, or a solid. • Scientific Method • 1) Make an observation • 2) Ask a Question- Does sound travel best through a gas, a liquid, or a solid? • 3) Formulate a hypothesis. What do you think? Write your own hypothesis. • 4)Test the hypothesis. CAUTION! - DO NOT POP the bag of water . Also, you will be to remain very quiet to complete this lab!!!!!! 5) Analyze your data 6) Write a conclusion 7) Share your findings