Chapter 10: Waves Unit 3: Energy On the Move Table of Contents 10 10.3: The Behavior of WavesThe Behavior of Waves 10.1: The Nature of Waves 10.2: Wave PropertiesWave Properties
What’s in a wave? wave is a repeating disturbance or movement that transfers energy through matter or space. Examples? 10.1 The Nature of Waves
Waves and Energy 10.1 The Nature of Waves Click image to view movie
Waves and Energy Because it is moving, the falling pebble has energy. 10.1 The Nature of Waves As it splashes into the pool, the pebble transfers some of its energy to nearby water molecules, causing them to move. What you see is energy traveling in the form of a wave on the surface of the water.
Waves and Matter Imagine you’re in a boat on a lake. 10.1 The Nature of Waves Approaching waves bump against your boat, but they don’t carry it along with them as they pass.
Waves and Matter The waves don’t even carry the water along with them. Only the energy carried by the waves moves forward. 10.1 The Nature of Waves All waves have this property they carry energy without transporting matter from place to place.
Making Waves A wave will travel only as long as it has energy to carry. 10.1 The Nature of Waves
Making Waves It is the up-and-down motion of your hand that creates the wave. 10.1 The Nature of Waves Anything that moves up and down or back and forth in a rhythmic way is vibrating. The vibrating movement of your hand at the end of the rope created the wave. In fact, -All waves are produced by something that vibrates.
Mechanical Waves Medium- matter the waves travel through is called a The medium can be a solid, a liquid, or gas 10.1 The Nature of Waves
Mechanical Waves Not all waves need a medium. 10.1 The Nature of Waves Light and radio waves, can travel through space. (No Medium) mechanical waves- Waves that can travel only through a medium. The two types of mechanical waves are transverse waves and compressional waves.
Transverse Waves transverse wave, Waves move at right angles to the direction that the wave travels. (Like water waves) 10.1 The Nature of Waves For example, a water wave travels horizontally as the water moves vertically up and down.
Compressional Waves compressional wave, waves move the same direction that the wave travels. 10.1 The Nature of Waves You can model compressional waves with a coiled spring toy.
Compressional Waves 10.1 The Nature of Waves Squeeze several coils together at one end of the spring. Then let go of the coils.
Compressional Waves As the wave moves, it looks as if the whole spring is moving toward one end. 10.1 The Nature of Waves The wave carries energy, but not matter, forward along the spring. Compressional waves also are called longitudinal waves.
Sound Waves Sound waves are compressional waves. 10.1 The Nature of Waves When a noise is made, such as when a locker door slams shut and vibrates, nearby air molecules are pushed together by the vibrations.
Sound Waves The air molecules are squeezed together like the coils in a coiled spring toy are when you make a compressional wave with it. 10.1 The Nature of Waves The compressions travel through the air to make a wave.
Sound in Other Materials Sound waves also can travel through other mediums, such as water and wood. 10.1 The Nature of Waves When a sound wave reaches your ear, it causes your eardrum to vibrate. Your inner ear then sends signals to your brain, and your brain interprets the signals as sound.
Water Waves 10.1 The Nature of Waves Ocean waves are formed most often by wind blowing across the ocean surface. The size of the waves that are formed depend on the wind speed, the distance over which the wind blows, and how long the wind blows.
Seismic Waves 10.1 The Nature of Waves Forces in Earth’s crust can cause regions of the crust to shift, bend, or even break. The breaking crust vibrates, creating seismic (SIZE mihk) waves that carry energy outward.
Seismic Waves 10.1 The Nature of Waves Seismic waves are a combination of compressional and transverse waves. They can travel through Earth and along Earth’s surface. The more the crust moves during an earthquake, the more energy is released. Click image to view movie
10.1 Section Check Question 1 What is a wave? A wave is a repeating movement that transfers energy through matter or space. Answer
10.1 Section Check Question 2 Which is carried by a water wave? A. a boat on the surface B. boat anchor submerged 50 m C. energy D. water molecules
10.1 Section Check Answer The answer is C. Waves carry energy without transporting matter from place to place.
10.1 Section Check Question 3 Which type of wave does not need a medium? A. electromagnetic B. mechanical C. ocean D. sound
10.1 Section Check Answer The answer is A. Electromagnetic waves are made by vibrating electric charges and can travel through space where matter is not present.
The Parts of a Wave Waves can differ in how much energy they carry and in how fast they travel. Waves also have other characteristics that make them different from each other. 10.2 Wave Properties
The Parts of a Wave crests - Alternating high points troughs - Alternating low points 10.2 Wave Properties
The Parts of a Wave Parts of a compressional wave Compression- region where the coils are close together. 10.2 Wave Properties
The Parts of a Wave Rarefaction- region where coils are spread apart 10.2 Wave Properties
Wavelength wavelength is the distance between two of the same points on a wave 10.2 Wave Properties
Wavelength The wavelengths of sound waves that you can hear range from a few centimeters for the highest-pitched sounds to about 15 m for the deepest sounds. 10.2 Wave Properties
Frequency and Period frequency of a wave is the number of wavelengths that pass a fixed point each second. transverse waves- number of crests that pass by a point each second. 10.2 Wave Properties Frequency is expressed in hertz (Hz).
Frequency and Period Period- amount of time it takes one wavelength to pass a point. 10.2 Wave Properties
Wavelength is Related to Frequency As frequency increases, wavelength decreases. 10.2 Wave Properties If you move the rope up, down, and back up in 1 s, the frequency of the wave you generate is 1 Hz.
Sound travel faster in liquids and solids than they do in gases. Light waves travel more slowly in liquid and solids than they do in gases or in empty space. 10.2 Wave Properties Sound waves faster in a material if the temperature of the material is increased. Sound and Mediums
Calculating Wave Speed You can calculate the speed of a wave represented by v by multiplying its frequency times its wavelength. 10.2 Wave Properties
Amplitude and Energy Amplitude energy carried by a wave. 10.2 Wave Properties The greater the wave’s amplitude is, the more energy the wave carries. Click image to play movie
Amplitude of Compressional Waves The closer the coils are in a compression, the farther apart they are in a rarefaction. 10.2 Wave Properties
Amplitude of Transverse Waves 10.2 Wave Properties Draw Picture
10.2 Section Check Question 1 If a wave has a high point and a low point, is it a compressional or transverse wave?
10.2 Section Check Transverse waves have alternating high points, called crests, and low points, called troughs. Answer
10.2 Section Check Question 2 What is the wavelength of a wave?
10.2 Section Check Answer A wavelength is the distance between one point on a wave and the nearest point just like it.
10.2 Section Check Question 3 Which of the following refers to the number of wavelengths that pass a fixed point each second? A. frequency B. period C. wavelength D. wave speed
10.2 Section Check Answer The answer is A. Period is a length of time, and wavelength is a distance.
To Be a Wave All waves must- Reflect, Refract, and Diffract. 10.3 The Behavior of Waves
Reflection How does the reflection of light allow you to see yourself in the mirror? It happens in two steps. First, light strikes your face and bounces off. Then, the light reflected off your face strikes the mirror and is reflected into your eyes. What about Sound Waves 10.3 The Behavior of Waves
Echoes Echo - sound waves hit an object, they reflect and come back to you. You hear the sound multiple times. 10.3 The Behavior of Waves
The Law of Reflection The beam striking the mirror is called the incident beam. 10.3 The Behavior of Waves The beam that bounces off the mirror is called the reflected beam. Draw this Picture:
The Law of Reflection 10.3 The Behavior of Waves The line drawn perpendicular to the surface of the mirror is called the normal.
The Law of Reflection The angle formed by the incident beam and the normal is the angle of incidence. 10.3 The Behavior of Waves The angle formed by the reflected beam and the normal is the angle of refection.
The Law of Reflection law of reflection- The angle of incidence is equal to the angle of refection. All reflected waves obey this law. 10.3 The Behavior of Waves
Refraction When a wave passes from one medium to another. It changes speed and direction. (Example: from air to water) 10.3 The Behavior of Waves If the wave is traveling at an angle when it passes from one medium to another, it changes direction, or bends, as it changes speed.
Refraction Refraction- Bending of a wave caused by a change in its speed as it moves from one medium to another. 10.3 The Behavior of Waves
Light waves travel slower in water than in air. This causes light waves to change direction and bend toward the normal 10.3 The Behavior of Waves When light waves travel from air to water, they slow down and bend toward the normal. Refraction of Light in Water
You may have noticed that objects that are underwater seem closer to the surface than they really are. 10.3 The Behavior of Waves In the figure, the light waves reflected from the swimmer’s foot are refracted away from the normal and enter your eyes.
Refraction of Light in Water However, your brain assumes that all light waves have traveled in a straight line. 10.3 The Behavior of Waves The light waves that enter your eyes seem to have come from a foot that was higher in the water.
Diffraction When waves strike an object, several things can happen. 10.3 The Behavior of Waves The waves can bounce off, or be reflected. If the object is transparent, light waves can be refracted as they pass through it. Waves also can behave another way when they strike an object. The waves can bend around the object.
Diffraction Diffraction - an object causes a wave to change direction and bend around it. 10.3 The Behavior of Waves Diffraction and refraction both cause waves to bend. The difference is that refraction occurs when waves pass through an object, while diffraction occurs when waves pass around an object.
Diffraction 10.3 The Behavior of Waves After they pass through the opening, the waves spread out.
Diffraction and Wavelength Examples of diffraction? 10.3 The Behavior of Waves
Hearing Around Corners 10.3 The Behavior of Waves Light waves have a much shorter wavelength. They are hardly diffracted at all by the door.
Diffraction of Radio Waves AM radio waves have longer wavelengths than FM radio waves do. Because of their longer wavelengths, AM radio waves diffract around obstacles like buildings and mountains. 10.3 The Behavior of Waves As a result, AM radio reception is often better than FM reception around tall buildings and natural barriers such as hills.
Interference interference When two or more waves overlap and combine to form a new wave 10.3 The Behavior of Waves
Constructive Interference constructive interference- waves add together. 10.3 The Behavior of Waves
Constructive Interference 10.3 The Behavior of Waves
Destructive Interference destructive interference- waves cancel each other. 10.3 The Behavior of Waves
Standing Waves standing wave - waves equal in wavelength and amplitude, travel in opposite directions, and interfere with each other. 10.3 The Behavior of Waves
Standing Waves in Music When the string of a violin is played with a bow, it vibrates and creates standing waves. 10.3 The Behavior of Waves Some instruments, like flutes, create standing waves in a column of air.
Resonance resonance - object is made to vibrate by absorbing energy at its natural frequency 10.3 The Behavior of Waves If enough energy is absorbed, the object can vibrate so strongly that it breaks apart.
10.3 Section Check Question 1 State the law of reflection. Answer According to the law of reflection, the angle of incidence is equal to the angle of reflection.
10.3 Section Check Question 2 __________ is the bending of a wave caused by a change in its speed as it moves from one medium to another. A. diffraction B. diffusion C. refraction D. reflection
10.3 Section Check Answer The answer is C. The greater the change in speed is, the more the wave bends.
10.3 Section Check Question 3 Which is the means by which you can hear around corners? A. diffraction B. diffusion C. reflection D. refraction
10.3 Section Check Answer The answer is A. Diffraction occurs when an object causes a wave to change direction and bend around it.
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