1. Chapter 20
Section 1 The Nature of Waves
Bellringer
What do you think of when you hear the word wave? Write a brief description of what you think a wave is. Then, write a short paragraph describing a time you might have experienced waves.

2. Chapter 20
Section 1 The Nature of Waves
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.

3. Chapter 20
Section 1 The Nature of Waves
Wave Energy
A wave is any disturbance that transmits energy through matter or empty space.
Energy can be carried away from its source by a wave. However, the material through which the wave travels does not move with the energy.

4. Chapter 20
Section 1 The Nature of Waves

5. Chapter 20 Wave Energy, continued
Section 1 The Nature of Waves
Wave Energy, continued
Waves and Work As a wave travels, it does work on everything in its path.
The waves in a pond do work on the water to make it move up and down. The waves also do work on anything floating on the water’s surface.
The fact that the water and floating objects move tells you that the waves are transferring energy.

6. Chapter 20 Wave Energy, continued
Section 1 The Nature of Waves
Wave Energy, continued
Energy Transfer Through a Medium Most waves transfer energy by the vibration of particles in a medium. A medium is a substance through which a wave can travel.
Sound waves, water waves, and seismic waves all need a medium through which to travel.

7. Chapter 20 Wave Energy, continued
Section 1 The Nature of Waves
Wave Energy, continued
Energy Transfer Without a Medium Visible light waves, microwaves, radio waves, and X rays are examples of waves can transfer energy without going through a medium.
These waves are electromagnetic waves. Although electromagnetic waves do not need a medium, they can go through matter.

8. Chapter 20
Section 1 The Nature of Waves
Types of Waves
Transverse Waves are waves in which the particles vibrate perpendicularly to the direction the wave is traveling.
Transverse waves are made up of crests and troughs.
Water waves, waves on a rope, and electromagnetic waves are examples of transverse waves.

9. Types of Waves, continued
Chapter 20
Section 1 The Nature of Waves
Types of Waves, continued
Longitudinal Waves are waves in which the particles vibrate back and forth along the path that the waves moves.
Longitudinal waves are made up of compressions and rarefactions.
Waves on a spring are longitudinal waves.

10. Chapter 20
Section 1 The Nature of Waves

11. Types of Waves, continued
Chapter 20
Section 1 The Nature of Waves
Types of Waves, continued
Sound Waves are longitudinal waves. Sound waves travel by compressions and rarefactions of air particles, as shown below.

12. Types of Waves, continued
Chapter 20
Section 1 The Nature of Waves
Types of Waves, continued
Combinations of Waves A transverse waves and a longitudinal wave can combine to form a surface wave.
Surface waves look like transverse waves, but the particles of the medium move in circles rather than up and down.