Introduction to Waves

Introduction to Waves

Middle School

​

Learning Objectives

Key Vocabulary

​

Wave

A wave is a disturbance that transfers energy from one place to another, but it does not transfer matter.

​

Medium

A medium is the substance or material, such as solid, liquid, or gas, through which a mechanical wave travels.

​

Amplitude

Amplitude is a wave's maximum movement from its rest position and is directly related to the wave's energy.

​

Wavelength

Wavelength is the specific distance over which the complete shape of a wave repeats itself from one point to the next.

​

Frequency

Frequency measures the total number of complete waves that pass a specific point within a given period of time.

​

Pitch

Pitch is the quality of a sound that is determined by the human ear's perception of its frequency.

Key Vocabulary

​

Loudness

Loudness is the human perception of the energy carried by a sound wave.

​

Reflection

Reflection is the bouncing back of a wave when it hits a surface or boundary.

​

Absorption

Absorption occurs when the energy from a wave is transferred into the medium it encounters.

​

Transmission

Transmission is the process of a wave passing through a medium or an object.

​

Refraction

Refraction is the bending of a wave as it passes from one medium to another.

​

Diffraction

Diffraction is the bending of waves as they move around an obstacle or an opening.

​

​

What is a Wave?

• A wave is a disturbance that transfers energy, not matter, between places.

• The source of any wave is a back-and-forth or up-and-down vibration.

• A mechanical wave is a wave that must travel through matter.

• Energy moves from particle to particle, like clapping creating sound waves.

​

Multiple Choice

Which statement best defines a wave?

• A disturbance that transfers energy

• A medium that transfers matter

• A vibration that creates matter

• A force that stops all motion

Multiple Choice

How does a mechanical wave transfer energy?

• A vibration causes particles of matter to pass energy along.

• Energy is created by the wave as it moves through matter.

• The wave transfers the particles themselves from place to place.

• A vibration can only happen if there is no matter present.

Multiple Choice

If a person claps their hands inside a vacuum (a space with no matter), no sound is heard. What is the best explanation for this?

• Sound is a mechanical wave and cannot travel without matter.

• The clap was not strong enough to create a vibration.

• Energy can only be transferred, not created by a clap.

• The wave would transfer matter but not energy in a vacuum.

​

​

Types of Mechanical Waves

Transverse Waves

• ​In a transverse wave, the disturbance moves perpendicular to the direction the wave travels.

• ​​Imagine shaking a rope up and down; the wave moves horizontally, but the rope moves vertically.

• ​The highest point of the wave is the crest, and the lowest point is the trough.

Longitudinal Waves

• ​In a longitudinal wave, particles of the medium move parallel to the wave's direction.

• ​​Think of pushing and pulling a spring to create this type of wave motion.

• ​It has compressions where particles are close and rarefactions where they are spread apart.

Multiple Choice

What is the key characteristic of a transverse wave?

• The disturbance moves parallel to the direction the wave travels.

• The disturbance moves perpendicular to the direction the wave travels.

• The wave has compressions and rarefactions.

• The wave has a crest and a trough.

Multiple Choice

What is the primary difference used to classify transverse and longitudinal waves?

• The relationship between how particles move and how the wave travels.

• The material that the wave is moving through.

• The height of the wave's crest and the depth of its trough.

• The distance between the wave's compressions.

Multiple Choice

If a student creates a wave by pushing and pulling a spring, what type of wave is produced and why?

• A transverse wave, because the wave has high and low points.

• A longitudinal wave, because the coils of the spring move parallel to the direction of the wave.

• A transverse wave, because the spring is being pushed and pulled.

• A longitudinal wave, because the wave has crests and troughs.

Examples of Waves

• Sound waves are longitudinal, with compressions and rarefactions.

• Water particles move in a circular path.

• Seismic P-waves are longitudinal, while S-waves are transverse.

Multiple Choice

In a longitudinal wave, what are the areas called where particles are crowded together and where they are spread apart?

• Crests and troughs

• Compressions and rarefactions

• Peaks and valleys

• Amplitudes and frequencies

Multiple Choice

Which statement correctly classifies two of the waves based on the information provided?

• Sound waves and seismic P-waves are both longitudinal.

• Seismic S-waves and water waves are both transverse.

• Water waves and sound waves are both circular.

• Seismic P-waves and seismic S-waves are both longitudinal.

Multiple Choice

What general conclusion can be drawn by comparing the particle motion of sound, water, and seismic waves?

• All waves cause particles to move in the same fundamental way.

• Different types of waves are characterized by distinct patterns of particle motion.

• Only seismic events can produce more than one type of wave motion.

• Longitudinal waves and circular waves are variations of transverse waves.

Wave Properties: Amplitude and Energy

Multiple Choice

What is the direct effect of increasing a wave's amplitude?

• The energy it carries increases.

• The energy it carries decreases.

• Its speed doubles.

• Its speed is cut in half.

Multiple Choice

If the amplitude of a wave is doubled, how does the amount of energy it carries change?

• The energy becomes four times greater.

• The energy doubles.

• The energy is halved.

• The energy does not change.

Multiple Choice

A pebble dropped in a pond creates waves. If you measure the wave's amplitude near the drop point and then again farther away, what would you expect to find and why?

• A wave with a smaller amplitude, because its energy decreased as it traveled.

• A wave with a larger amplitude, because waves gain energy over distance.

• A wave with the same amplitude, because energy is constant.

• No wave at all, because the energy was completely lost.

Wave Properties: Wavelength and Frequency

• Wavelength is the distance between two consecutive crests or troughs of a wave.

• Frequency is the number of waves passing a point in a certain time.

• As a wave's frequency increases, its wavelength must decrease.

Multiple Choice

What is the term for the distance between two consecutive crests or troughs of a wave?

• Wavelength

• Frequency

• Amplitude

• Wave Speed

Multiple Choice

If the frequency of a wave increases, what happens to its wavelength?

• The wavelength decreases.

• The wavelength increases.

• The wavelength stays the same.

• The wavelength becomes zero.

Multiple Choice

If Wave A has crests that are farther apart than the crests of Wave B, what can be concluded about their frequencies?

• Wave A has a lower frequency than Wave B.

• Wave A has a higher frequency than Wave B.

• Both waves have the same frequency.

• Frequency cannot be determined from the distance between crests.

Introduction to Light Waves

• Light waves are electromagnetic and can travel through the vacuum of space.

• A light wave's amplitude is its brightness, and its frequency is its color.

• Light travels in a straight line until it interacts with a material.

Multiple Choice

What is a defining characteristic of light waves?

• They must have a medium to travel.

• They are a form of sound energy.

• They can travel through the vacuum of space.

• They are unable to travel in straight lines.

Multiple Choice

What is the relationship between a light wave's properties and how we perceive it?

• The wave's amplitude determines its color, while its frequency determines its brightness.

• The wave's speed determines its brightness, while its size determines its color.

• The wave's amplitude determines its speed, while its frequency determines its path.

• The wave's amplitude determines its brightness, while its frequency determines its color.

Multiple Choice

If a beam of light is traveling in a straight line across a room, what would cause its path to change?

• Increasing the brightness of the light.

• Changing the color of the light.

• Making the room completely dark.

• Placing a mirror in the beam's path.

Wave Interactions: Reflection, Absorption, & Transmission

​

Reflection

• A wave bounces off a surface it encounters.

• Light reflection allows us to see objects in mirrors.

• An echo is simply a reflection of a sound wave.

​

Absorption

• A wave transfers its energy into the medium.

• Dark surfaces absorb more light energy, creating heat.

• Light-colored surfaces reflect more light energy instead.

​

Transmission

• A wave passes directly through a medium or substance.

• This allows us to see through transparent materials.

• Examples include light passing through glass or water.

Multiple Choice

What is the process called when a wave bounces off a surface it encounters?

• Reflection

• Absorption

• Transmission

• Refraction

Multiple Choice

What is the relationship between a dark-colored surface and heat when exposed to light?

• The dark surface absorbs more light energy, which is converted to heat.

• The dark surface reflects more light energy, which creates warmth.

• The light-colored surface transmits more energy, making it feel cooler.

• The light-colored surface absorbs more energy, making the dark one feel warmer by comparison.

Multiple Choice

If a clear glass window is replaced with a dark, mirrored piece of glass, how will it interact with light?

• It would transmit all of the light through it.

• It would absorb all of the light, preventing any from passing through.

• It would reflect all of the light, acting as a perfect mirror.

• It would reflect some light, absorb some light, and transmit very little.

​

​

What is Refraction?

• Refraction is the bending of a wave as it enters a new medium.

• This happens because the wave’s speed changes when it enters the new medium.

• A straw in a glass of water appears bent because of refraction.

• Lenses in glasses and cameras use refraction to focus light and create images.

​

Multiple Choice

What is refraction?

• The bending of a wave as it enters a new medium

• The bouncing of a wave off of a surface

• The absorption of a wave by an object

• The blocking of a wave by a barrier

Multiple Choice

What causes a wave to bend when it undergoes refraction?

• The wave's speed changes.

• The wave's color changes.

• The wave gets louder.

• The wave stops moving.

Multiple Choice

Based on the principles of refraction, which statement best explains why lenses are used in cameras and glasses?

• They bend light to focus it, creating a clear image.

• They reflect light, making things appear brighter.

• They absorb light, reducing glare from the sun.

• They make light waves larger, magnifying the image.

​

​

Sound Waves: Speed and Diffraction

Speed of Sound

• ​The speed of a sound wave depends on the medium it travels through.

• ​​A medium's density and temperature affect how fast a sound wave can travel.

• ​Sound travels fastest through solids, slower in liquids, and slowest in most gases.

Diffraction

• ​Diffraction is the bending of a wave around an object or through an opening.

• ​​As a wave diffracts, it changes direction and spreads out from its path.

• ​This is why you can hear someone talking from around a corner.

Multiple Choice

What is the term for the bending of a wave as it passes around an object or through an opening?

• Diffraction

• Propagation

• Reflection

• Resonance

Multiple Choice

Which of the following best explains how the medium affects the speed of a sound wave?

• Sound travels fastest through solids and slowest through most gases.

• Sound travels slowest through solids and fastest through most gases.

• The temperature of the medium does not affect the speed of sound.

• Sound travels at the same speed regardless of the medium.

Multiple Choice

If a sound is made in a room and the waves travel through an open doorway, why can a person in the next room hear the sound even if they are not in a direct line from the doorway?

• The sound waves bend and spread out as they pass through the doorway.

• The sound waves increase in speed as they enter the new room.

• The sound waves bounce directly off the walls into the person's ear.

• The sound waves travel only in a straight line from their source.

​

Common Misconceptions

Misconception	Correction
Waves transport matter.	Waves transfer energy. Particles of the medium only oscillate.
Louder sounds travel faster than quieter sounds.	Wave speed depends on the medium, not its amplitude.
Light always travels in a straight line.	Light bends (refracts) when it moves between different mediums.
Sound can travel through a vacuum.	Sound is a mechanical wave and requires a medium.

​

Summary

• Waves are repeating patterns that transfer energy through a medium or empty space.

• In light waves, amplitude determines brightness, and frequency determines the color we see.

• Waves interact with materials by reflection, absorption, transmission, refraction, and diffraction.

• A wave's speed is determined by the properties of the medium it travels through.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1

• 2

• 3

• 4