Forces & Motion Understand the properties of waves and the wavelike property

of energy in earthquakes, light and sound.

Monday

Learning Objective6.P.1.1 - Compare the properties of waves to the wavelike property of energy in earthquakes, light

and sound.

Vocabulary Words

❏ Amplitude ❏ Wavelength ❏ Frequency ❏ Reflection ❏ Absorption❏ Seismograms ❏ Surface waves ❏ S Waves❏ Mechanical Waves ❏ Electromagnetic Waves

❏ Transmittance ❏ Wave ❏ Hertz ❏ Nanometer ❏ Trough ❏ Seismographs ❏ P waves ❏ Transverse Waves ❏ Longitudinal Waves

WHAT IS WAVE REFLECTION, ABSORPTION & TRANSMITTANCE?

A wave is a repeating pattern of motion that transfers energy from place to place. When waves come in contact with an object, a few things can happen.

The wave can be transmitted, which means to pass through the object. It can be absorbed, in which the wave is converted to thermal energy, or it can be reflected (sent off in a new direction).

Waves have properties

A wave is a repeating pattern of motion that transfers energy from place to place. All waves have properties such as amplitude, wavelength, and frequency. These properties can be used to describe the wave.

Waves have properties

The amplitude of a wave determines pitch in sound waves and brightness in light waves.

Wavelength is the length of one wave.

Frequency is how many waves occur in 1 second.

The wavelength and frequency of a light wave determine color. A light wave is measured in

nanometers.

Different wavelengths produce different colors

Higher wavelengths produce brighter colors such as red, and lower wavelengths produce

darker colors such as violet.

Properties of a Wave

❏ Crest ❏ Amplitude ❏ Trough ❏ Wavelength

Sound waves travel through matter

❏ Sound waves need matter to travel through, but light waves do not. When sound travels through matter, they can be absorbed, reflected, or transmitted depending on the waves’ properties. Higher amplitude sound waves are more likely to be transmitted through matter instead of reflected.

❏ Lower amplitude sound waves are more likely to be reflected or absorbed, resulting in a lack of an echo. Sound can travel through air, water, and solids.

Wave AbsorptionWaves can be absorbed by matter, depending on what the matter is and the properties of the sound wave.

When a wave is absorbed, the matter takes in energy from the wave and, in doing so, lowers the amplitude.

Wave ReflectionWaves are reflected when the density of matter is too high for the wave to pass through or be absorbed. Because of that, the wave is reflected (or bounces off) and then moves in a different direction than it was originally traveling.

When sound waves are reflected, there is often an echo because the sound wave is traveling in various directions bouncing off matter. Part of the wave will attempt to pass through the solid, liquid, or gas, but most of the wave will bounce off and travel in a different direction.

The process of a sound wave repeatedly reflecting in a space is called reverberation.

Wave Transmittance

When light moves through liquid, like in a fish tank, it transmits certain colors while

absorbing others.

Because different colors of light have different wavelengths, some colors are reflected

while others are absorbed. This allows different wavelengths of light, and also colors, to be

reflected on the human eye, which allows us to see color!

Wave Motion

Tuesday

Wave Creation

Waves are created when a force, or an energy source, creates a vibration or disturbance. Waves always start at the source and move away from it, so the waves are moving outward.

Wave behavior can be described in terms of how fast the wave spreads and the distance between the peaks of the disturbance. These two wave properties are called the frequency and the wavelength.

Waves Transmit Energy, Not Matter

A wave is moving energy. The energy in a wave is transferred from one point to another, but

there is no net movement of the matter through which the wave is traveling.

Sound, light, and heat are some of the types of energy that move through waves. Earthquakes

create seismic waves that transmit energy through the interior of the Earth.

Wave Types

Waves can move through all types of matter, or media, and some waves can travel through

areas—such as the vacuum of space—that contain no matter at all.

Waves can be classified as either mechanical waves or electromagnetic waves based, in part,

on whether or not a medium must be present in order for them to travel.

Mechanical waves are waves that travel by making a substance, such as air or water, vibrate. If there is no substance, as is the case in outer space, a mechanical wave will stop moving.

Wave Types

Seismic waves are caused by earthquakes. When an earthquake moves the land, it causes it to vibrate. The seismic vibrations carry energy through the different layers of the Earth. These vibrations can be detected by scientists many hundreds of miles away.

Electromagnetic waves are different from mechanical waves in that electromagnetic waves can travel through the empty vacuum of outer space.

Mechanical Waves

Mechanical waves are created by the vibration of objects. Mechanical waves can be either transverse or longitudinal.

When an object vibrates, its vibrations from mechanical waves that can travel through solids, liquids, or gases in a series of ripples that spread away from the object and disturb nearby particles. As each particle is disturbed, it collides with the particle next to it. In this way, the wave moves through the material.

Example: a loud, low sound, such as music with heavy bass, creates ripples in the liquid inside a nearby glass.

Wednesday

Transverse & Longitudinal Waves

Mechanical waves can be classified based on how they affect the particles of a medium.

The two classifications of waves based on this criterion are transverse waves and

longitudinal waves.

Characteristics of Transverse Waves

There are 6 characteristics of transverse waves

Wavelength—the distance between one wave crest and the next (or between one wave trough and the next). Vibrations with long wavelengths also have lower frequencies than vibrations with shorter wavelengths. This is because fewer of the longer waves can travel a particular distance in a set amount of time.

Frequency—the number of complete waves or cycles that pass a fixed point in a specific unit of time. If a high frequency wave and a low frequency wave are traveling past the same point, more cycles of the high frequency wave will pass the point in the same amount of time.

Amplitude—the size of the displacement or change caused by the wave. At any given frequency, it takes more energy to create a wave with larger amplitude than to create a wave with smaller amplitude.

Characteristics of Transverse Waves

Speed—a measurement of how fast a wave passes through a medium. The more tightly

bound to each other the particles of a substance are, the faster a mechanical wave will

travel through that substance.

Crest—the point on a transverse wave with the greatest positive displacement from

equilibrium. In other words, a crest is the highest point of a wave (one wavelength).

Trough—the point on a transverse wave with the greatest negative displacement from

equilibrium. In other words, a trough is the lowest point of a wave (one wavelength).

Longitudinal Waves

The diagram below shows some of the wave characteristics of a longitudinal wave. Each

square represents an object, like a particle of matter, carrying the energy of the wave.

Longitudinal Waves

Sound waves are longitudinal waves when passing through liquids and gases but can be

transverse when passing through solids.

When a longitudinal wave travels through a medium, the medium moves back and forth

in the same direction in which the wave travels.

Characteristics of Longitudinal Waves

There are 6 characteristics of longitudinal waves

Wavelength—the distance from one point of compression to the next on a longitudinal wave (or from one point of rarefaction to the next on the wave).

Frequency—the number of complete waves or cycles that pass a fixed point in a specific unit of time. High frequency sound waves have higher pitch than low frequency waves. For example, sound created by striking a bass drum has a lower frequency and lower pitch than a sound created by a bird's song.

Rarefaction—the area of a longitudinal wave in which the molecules are the most spread apart. The rarefaction point of a longitudinal wave is similar to the trough of a transverse wave.

Characteristics of Longitudinal Waves

Amplitude—the size of the displacement or change caused by the wave. The larger the amplitude of a sound wave, the louder the sound.

Speed—a measurement of how fast a wave passes through a medium. The more tightly bound to each other the molecules of a substance are, the faster a mechanical wave will travel through that substance.

Compression—the area of a longitudinal wave in which the molecules are the most crowded together. The compression point of a longitudinal wave is similar to the crest of a transverse wave.

Transverse & Longitudinal Waves

Thursday

Earthquakes

Seismologists have studied how wave energy travels through different layers of Earth.

During an earthquake, energy is released into the Earth as primary waves, secondary waves, and surface waves.

Cause of Earthquakes

Forces applied to one lithospheric plate by another cause stress on the rocks that

compose the Earth's crust.

Compressional stress is applied where rocks push together.

Tensional stress is applied where rocks pull away from each other.

Shear stress is applied where rocks move horizontally alongside each other

Cause of Earthquakes

Over time, as more stress is applied, the rocks bend and begin to build up stored energy.

If more stress is applied than the rocks can withstand, they will break or slip along a fault,

releasing the built-up energy. The energy is released as earthquake waves.

Earthquake waves travel outward in all directions from the earthquake's underground

origin, or its focus.

The point on the Earth's surface directly above the focus is the earthquake's epicenter.

Earthquake Waves

There are three basic types of earthquake waves, or seismic waves

Primary (P) waves are the fastest type of seismic wave and originate at the earthquake

focus. These waves travel directly through solids and liquids in the Earth's interior. P

waves are longitudinal. Therefore, as P waves travel through matter, the particles of

matter move back and forth along the direction of wave travel.

Earthquake Waves

Secondary (S) waves are the second fastest type of seismic wave and, like P waves, originate at the earthquake focus. S waves travel directly through the Earth's interior like P waves, but S waves can travel only through solids. As S waves travel through particles, the particles move back and forth perpendicular to the direction of wave travel. S waves are a type of transverse wave.

Surface waves are the slowest type of seismic wave but also the most destructive. These waves form when P waves or S waves reach the surface. There are several different kinds of surface waves that cause the ground to move in different ways. But all surface waves travel along the Earth's surface. Surface wave energy is always strongest at the earthquake epicenter. Surface waves often do the most damage of all the types of waves.

Applications of Seismic Waves

Scientists study and use seismic waves in many ways. The differences between P waves and S waves

have allowed scientists to determine the structure of Earth's interior.

For example, there is a certain zone through which S waves will not travel through the Earth. This is

because S waves cannot travel through fluids. By carefully mapping out this zone, scientists have

determined that the Earth's outer core is made of liquid.

Applications of Seismic Waves

Scientists also use seismic waves to map locations of earthquake epicenters. Scientists measure seismic waves on instruments called seismographs.

The arrival time and intensity of each kind of seismic wave is recorded by the seismograph onto readings called seismograms.

By measuring the difference in arrival times of P and S waves at several seismograph stations, scientists can use triangulation to pinpoint the earthquake's epicenter.

Only three seismograph stations are needed to locate an epicenter, but using more stations increases location accuracy.

Key Points about Waves

❏ All waves transmit energy not matter. Nearly all waves travel through matter.

❏ Waves are created when a source (force) creates a vibration. Vibrations in materials set up wavelike disturbances that spread away from the source

❏ Wave behavior can be described in terms of how fast the disturbance spreads, and in terms of the distance between successive peaks of the disturbance (the wavelength).

❏ Sound and earthquake waves are examples. These and other waves move at different speeds in different materials. Waves are moving energy.

Key Points about Waves

❏ Light waves are unique in their ability to travel through a vacuum (space).

❏ Sound is a form of energy that results when vibrating materials produce waves that move through matter.

❏ Earthquakes are vibrations in the earth that release the (potential) energy stored in rocks (due to their relative positions and consequent pressure).

❏ Earthquakes create seismic waves. Compare sound waves (longitudinal waves) to light waves (transverse waves). Energy will cause materials to vibrate.

❏ These vibrations are carried as “waves” and transfer energy.