Interest Grabber Section 17 1 Vibrations A wave

Interest Grabber Section 17. 1 Vibrations A wave is a vibration that carries energy from one place to another. But not all vibrations are waves. Hold a pen lightly between your thumb and index finger. Shake your hand back and forth to make the pen seem to bend like it’s made of rubber. Next, hold a length of string (about 1 meter long) at one end. Shake the end of the string back and forth. Observe the vibrations. 1. Describe the motion of the pen and the motion of the string. 2. In which case did the vibration move from one place to another? In which case did the vibration stay in one place? Go to section

Mechanical Waves • A Mechanical wave is a disturbance in matter that carries energy from one place to another. • Mechanical waves require a medium (solid, liquid or gas) to travel through. Go to section

Transverse Waves • Transverse Waves • As the wave travels from one point to another, each individual particle only travels perpendicular to the direction the wave travels. • Each particle experiences no net movement as the energy passes through it. Go to section

Transverse Waves Go to section Figure 2

Longitudinal Waves • Longitudinal Waves • As the wave travels from one point to another, each individual particle travels parallel to the direction the wave travels. • Each particle experiences no net movement as the energy passes through it. Go to section

Longitudinal Waves Go to section Figure 3

Surface Waves • Surface waves travel at the surface separating two media. Go to section

Surface Waves Go to section Figure 4

Interest Grabber Section 17. 2 Waves Carry Energy When a wave travels through a medium, the wave carries energy, not particles, from one place to another. You can measure the speed of a wave by how fast energy moves from one place to another. To model a wave’s energy transfer, stand in a line with your classmates. The first person in the line should slowly pass a book to the second person. The second person should pass it to the third person, and so on down the line. Repeat the activity, but this time pass the book quickly. 1. What did the book represent? 2. How would you describe the speed of the wave in each case? Go to section

Frequency and Wavelength of Transverse Waves Frequency is how many cycles in a second Go to section Figures 5 and 6 Wavelength is the distance between 2 crests

Wave speed • Recall Speed = distance time Wave Speed = wavelength x frequency Go to section

Speed of Mechanical Waves Go to section Section 17. 2

Speed of Mechanical Waves Go to section Section 17. 2

Speed of Mechanical Waves Go to section Section 17. 2

Speed of Mechanical Waves Go to section Section 17. 2

Amplitude of Transverse Waves Section 17. 2 Amplitude of a wave is the maximum displacement from the rest position The more energy a wave has, the greater the amplitude Go to section

Interest Grabber Section 17. 3 Reflected Waves What happens when a wave hits a wall or some other fixed object? To find out, tie a rope to the back of a chair. Gently shake the rope up and down once to send a single pulse along the rope as shown. Observe what happens when the pulse hits the chair. 1. What happened to the direction of the pulse when it hit the chair? 2. How did the orientation of the reflected pulse compare to the original pulse? Go to section

Reading Strategy Section 17. 3 Identifying Main Ideas a. If reflection occurs at a fixed boundary, the reflected wave will be upside down compared to the original wave. b. Refraction occurs when a wave enters a new medium at an angle because one side of a wave front moves more slowly than the other side. c. The larger the wavelength is compared to the size of an opening or obstacle, the more a wave diffracts. d. The types of interference are constructive and destructive interference. Go to section e. A standing wave forms only if a multiple of one half wavelength fits exactly into the length of the vibrating object.

Reflection & Refraction • Reflection occurs when a wave bounces off a surface that it cannot pass through. – Reflection does not change the speed or frequency of a wave, but can be flipped upside down. • Refraction is the bending of a wave as it enters a new medium and changes speed. – The wave will bend as it speeds up or slows down. Go to section

Diffraction • Diffraction – bending of a wave around an obstacle or through a narrow opening Go to section

Constructive vs. Destructive Interference of Waves Figure 12 Constructive interference occurs when two or more waves combine to produce a larger wave with the same frequency. Ex. Two speakers will be louder than one. Go to section

Constructive vs. Destructive Interference of Waves Figure 12 Destructive Interference occurs when two or more waves combine to produce a smaller wave of the same frequency. Ex. Two speakers cancel each other out and produce a quieter sound. Go to section

Interest Grabber Section 17. 4 Can You Hear Through Your Desk? Sound waves travel through a medium as energy is passed from particle to particle. If the particles are close together, as in a solid, the sound generally travels faster and less energy is lost. Listen carefully to the sound as you knock on your desk. Note how far your ear is from your hand when you make the sound. Without changing this distance, place your ear against your desk and knock again. 1. In each case, how did the sound travel to your ears? 2. What was the difference in the sound when you held your ear against the desk? Go to section

The Speed of Sound in Different Mediums Go to section Figure 14

Sound Waves • Sound waves are longitudinal- compressions and rarefactions that travel through a medium • Many behaviors of sound can be explained using a few properties • Speed, intensity and loudness, and frequency and pitch Go to section

• Intensity is the rate at which a wave’s energy flows through a given area. • Sound intensity depends on both the wave’s amplitude and the distance from the source. • Sound intensity levels are measured in decibels (d. B) • Loudness is a physical response to the intensity of sound. Go to section

• Pitch is the frequency of sound as you perceive it. • Pitch depends on a wave’s frequency. • High frequency-high pitch • Low frequency- low pitch Go to section

• Ultrasound-sound frequencies lower than 20 hertz • Human hearing- 20, 000 hz • Ultrasound is used in sonar and ultrasound imaging • Sonar is a technique for determining the distance to an object under water. (time it takes a sound to reach an object under water and the echo to return. ) • Ultrasound uses a pulse or short burst of a wave 1/8000 of a second. Computer software makes a detailed map of the image. Go to section

Doppler Effect • Doppler Effect- a change in sound frequency caused by motion of the sound source, motion of the listener, or both. • As a source of sound approaches, an observer hears a higher frequency. When the sound source moves away, the observer hears a lower frequency. Go to section

The Doppler Effect Go to section Figure 18

The outer ear • The outer ear gathers and focuses sound into the middle ear. • The middle ear receives and amplifies the vibrations using the Hammer, Anvil, and Stirrup. • The inner ear uses nerve endings to sense vibrations and send signals to the brain. Go to section

The Anatomy of the Ear Go to section Figure 19

• Most musical instruments vary pitch by changing the frequency of standing waves. • Resonance is the response of a standing wave to another wave of the same frequency. Go to section