Waves

Waves

Middle School

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Learning Objectives

• Define a wave and explain how it transfers energy through a medium.

• Differentiate between mechanical and electromagnetic waves.

• Describe the types of mechanical waves: transverse, longitudinal, and surface waves.

• Identify the key characteristics of waves, including amplitude, wavelength, and frequency.

• Explain wave behaviors such as interference, resonance, and the Doppler effect.

Key Vocabulary

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Wave

A disturbance that transfers energy from one place to another without permanently moving any matter.

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Medium

The matter or substance, such as a solid, liquid, or gas, through which a wave travels.

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Mechanical Wave

A wave that needs a medium like a solid, liquid, or gas in order to travel.

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Transverse Wave

A wave where medium particles vibrate up and down, perpendicular to the direction the wave is traveling.

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Longitudinal Wave

A wave where the medium's particles vibrate back and forth, parallel to the wave's travel direction.

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Amplitude

The maximum distance that particles of the medium move away from their normal resting position.

Key Vocabulary

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Wavelength

The distance from one point on a wave to the identical point on the next wave.

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Frequency

The number of complete waves or cycles that pass a certain point per second.

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Interference

The phenomenon that occurs when two waves meet and combine to create a new wave.

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Resonance

Occurs when a forced vibration matches an object's natural frequency, increasing its amplitude.

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Doppler Effect

The apparent change in a wave's frequency due to motion between the source and observer.

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What Are Waves?

• A wave is a disturbance that transfers energy from one place to another.

• Importantly, waves transfer this energy without transferring matter from the source.

• All waves are caused by a disturbance or vibration that provides the initial energy.

• The material a wave travels through to transport energy is called a medium.

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Multiple Choice

What is the primary role of a wave?

• To transfer energy from one place to another

• To create a disturbance in a medium

• To stop vibrations from happening

• To move matter from one place to another

Multiple Choice

What is the relationship between a disturbance and a medium?

• A medium creates a disturbance that stops a wave.

• A medium is a type of disturbance.

• A disturbance is a type of medium.

• A disturbance can cause a wave that travels through a medium.

Multiple Choice

If you throw a rock into a still pond, a wave travels to the edge. Which statement best explains what happens to the water molecules in the middle of the pond?

• The water molecules are destroyed by the energy of the wave.

• The water molecules vibrate but stay in roughly the same place.

• The water molecules travel with the wave to the edge of the pond.

• The water molecules are converted into energy by the disturbance.

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Types of Waves: Mechanical vs. Electromagnetic

Mechanical Waves

• ​These waves require a medium, such as a solid, liquid, or gas, to travel.

• ​​Energy is transferred when particles of the medium vibrate and collide with each other.

• ​Examples include sound waves, ocean waves, and seismic waves from an earthquake.

Electromagnetic Waves

• ​These waves do not require a medium and can travel through the vacuum of space.

• ​​They are composed of vibrating electric and magnetic fields that travel together.

• ​Examples include radio waves, microwaves, and the visible light from the sun.

Multiple Choice

What is the main difference between mechanical and electromagnetic waves?

• Mechanical waves are made of electric fields, while electromagnetic waves are made of particles.

• Mechanical waves only travel through solids, while electromagnetic waves only travel through gases.

• Mechanical waves require a medium to travel, while electromagnetic waves do not.

• Mechanical waves are always visible, while electromagnetic waves are always invisible.

Multiple Choice

How do mechanical waves, like sound waves, transfer energy?

• Through vibrating electric and magnetic fields that travel together.

• By traveling through the vacuum of space without any medium.

• By converting energy into light that can be seen from a distance.

• Through the vibration and collision of particles within a medium.

Multiple Choice

An explosion occurs in outer space. An astronaut sees the flash of light but does not hear any sound. What is the best explanation for this observation?

• The sound waves are too quiet to be heard in space.

• Sound waves travel much slower than light waves and have not reached the astronaut yet.

• Light is an electromagnetic wave that can travel through a vacuum, but sound is a mechanical wave that cannot.

• The astronaut's helmet blocks out all sound waves but allows light to pass through.

Types of Mechanical Waves

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Transverse Wave

• ​Particles vibrate perpendicular to the direction the wave is traveling.

• ​​This creates a distinct up-and-down movement in the medium.

• ​Shaking a rope up and down makes a transverse wave.

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Longitudinal Wave

• ​Particles vibrate parallel to the direction of the wave's motion.

• ​​This parallel vibration creates a back-and-forth motion for particles.

• ​Sound waves are a key example of longitudinal waves.

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Surface Wave

• ​This is a combination of transverse and longitudinal waves.

• ​​Particles of the medium move in a circular motion.

• ​Waves on the surface of water are surface waves.

Multiple Choice

What defines a longitudinal wave?

• Particles of the medium move in a circular motion.

• Particles of the medium do not move from their position.

• Particles vibrate perpendicular to the direction of the wave's motion.

• Particles vibrate parallel to the direction of the wave's motion.

Multiple Choice

How does the particle movement in a transverse wave compare to that in a longitudinal wave?

• Transverse waves have perpendicular movement, while longitudinal waves have parallel movement.

• In both waves, particles move parallel to the wave's direction.

• Transverse waves have parallel movement, while longitudinal waves have perpendicular movement.

• In both waves, particles move in a circular pattern.

Multiple Choice

A floating object on the water is observed moving in a circular pattern as a wave passes. What can be concluded about this type of wave?

• It is not a type of mechanical wave.

• It is only a transverse wave.

• It is a combination of transverse and longitudinal waves.

• It is only a longitudinal wave.

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Characteristics of Waves

Transverse Waves

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

• Amplitude is the maximum distance particles move from rest; for a transverse wave, it is the rest-to-crest distance.

• A wave with a higher amplitude is carrying a greater amount of energy.

Longitudinal Waves

• A compression is an area where particles are close together, and a rarefaction is where they are spread apart.

• Wavelength (λ) is the distance from any point on a wave to the identical point on the next wave.

• It can be measured from one crest to the next, or from one compression to the next.

Multiple Choice

What is the definition of a wave's wavelength?

• The distance from one point on a wave to the identical point on the next wave.

• An area where particles in a wave are spread far apart.

• The maximum distance particles move from a rest position.

• The highest point of a transverse wave.

Multiple Choice

What is the relationship between the amplitude of a transverse wave and the energy it carries?

• A wave with a higher amplitude carries a greater amount of energy.

• A wave's amplitude and energy are not related to each other.

• A wave with a higher amplitude carries less energy.

• A wave's amplitude is determined by its wavelength, not its energy.

Multiple Choice

A scientist observes two waves. Wave 1 has crests and troughs, while Wave 2 has compressions and rarefactions. Which statement accurately describes these two waves?

• Wave 1 is a transverse wave, and Wave 2 is a longitudinal wave.

• Both waves are transverse, but they have different wavelengths.

• Both waves are longitudinal, but they have different amplitudes.

• Wave 1 is a longitudinal wave, and Wave 2 is a transverse wave.

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Wave Properties: Frequency, Period, and Speed

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Multiple Choice

What does the frequency of a wave measure?

• The time it takes for one complete wave to pass a point.

• The height of a wave from its resting position.

• The number of waves that pass a point in one second.

• The total distance a wave travels in one minute.

Multiple Choice

What is the relationship between a wave's frequency and its wavelength?

• As frequency increases, wavelength decreases.

• As frequency increases, wavelength also increases.

• Frequency and wavelength are not related to each other.

• As frequency increases, wavelength stays the same.

Multiple Choice

A scientist observes that the time it takes for one full wave to pass by—the period—is getting shorter. If the wavelength of the wave remains constant, what must be happening to the wave's speed?

• The wave's speed is decreasing.

• The wave's speed is reversing direction.

• The wave's speed is staying the same.

• The wave's speed is increasing.

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What is Wave Interference?

• Interference happens when two waves of the same type meet and overlap.

• ​Constructive interference is when wave crests align, making a larger amplitude.

• Destructive interference is when a crest and a trough meet, canceling out.

• In sound, this creates beats, making the sound alternate from loud to soft.

Multiple Choice

What is the result of constructive interference between two waves?

• The frequency of the waves decreases, making them slower.

• The waves combine to create a wave with a higher, more intense amplitude.

• The waves reverse direction and travel away from each other.

• The waves cancel each other out, resulting in a smaller amplitude.

Multiple Choice

Which statement explains why destructive interference can make a sound quieter?

• A wave's amplitude is increased, making the sound more intense.

• Two sound waves combine to create a brighter pattern of light.

• The crests of two sound waves align and add together.

• A wave's crest meets another wave's trough, causing them to cancel out.

Multiple Choice

An audio engineer notices that in a concert hall, there is a specific spot where a certain musical note is almost silent. What is the most likely explanation for this?

• The sound waves from the speakers cannot reach that specific spot.

• The sound waves are experiencing destructive interference, causing them to cancel out.

• The sound waves are reflecting off the walls and changing frequency.

• The sound waves in that spot are experiencing constructive interference, making them louder.

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Wave Behavior: Reflection and Standing Waves

Reflection

• Reflection occurs when a wave hits a barrier and cannot pass through it.

• The wave bounces off the barrier and travels back in the opposite direction.

• If the barrier is fixed, the wave inverts, or flips upside down, upon reflection.

Standing Waves

• A standing wave is a wave pattern that appears to remain in a constant position.

• It is formed by the interference between a wave and its own reflected wave.

• It has points of no motion (nodes) and points of maximum motion (antinodes).

Multiple Choice

What happens when a wave hits a barrier it cannot pass through?

• The wave bounces off and travels back.

• The wave stops and disappears.

• The wave passes through the barrier.

• The wave gets larger and continues forward.

Multiple Choice

How does the process of reflection contribute to the formation of a standing wave?

• A standing wave is formed by the interference between a wave and its own reflection.

• Reflection causes the wave to stop, creating a stationary or 'standing' pattern.

• Reflection cancels out the original wave, leaving a standing wave behind.

• A standing wave is another term for a wave that has been inverted by reflection.

Multiple Choice

If a wave on a string reflects from a fixed end, it inverts. This reflected wave then interferes with the original wave to create a standing wave. What would you expect to find at the fixed end of the string?

• A point of maximum motion (an antinode)

• A point where the wave is still traveling forward

• A point where the wave passes through the end

• A point of no motion (a node)

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Wave Behavior: Resonance & Doppler Effect

Resonance

• Resonance occurs when an object is forced to vibrate at its natural frequency.

• When the two frequencies match, the amplitude of the vibration increases dramatically.

• This is how an opera singer can shatter a glass by singing the right note.

Doppler Effect

• This is the change in a wave's frequency due to relative motion.

• If the source and observer move closer, the frequency appears to get higher.

• If they move away from each other, the frequency appears to get lower.

Multiple Choice

What happens when an object is forced to vibrate at its natural frequency?

• The object produces a lower-pitched sound.

• The object's vibrations stop completely.

• The amplitude of the vibrations increases dramatically.

• The frequency of the vibrations decreases.

Multiple Choice

What is the underlying cause of the Doppler Effect?

• The matching of two different frequencies.

• The relative motion between a wave source and an observer.

• The increase in the amplitude of a wave.

• An object vibrating at its natural frequency.

Multiple Choice

A fire truck with its siren on is moving away from a person standing on a street corner. How will the sound of the siren seem to change to the person?

• The siren will sound like it has a lower frequency.

• The siren's volume will increase, but its frequency will be unchanged.

• The siren will sound like it has a higher frequency.

• The siren's frequency and volume will remain constant.

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Common Misconceptions

Misconception	Correction
Waves transfer matter.	Waves transfer energy, but the particles of the medium only vibrate in place.
All waves need a medium.	Only mechanical waves need a medium; electromagnetic waves can travel through a vacuum.
Faster vibrations mean a faster wave.	A wave's speed is determined by the properties of the medium.
The Doppler effect changes a wave's actual frequency.	It is an apparent change in frequency perceived by an observer due to relative motion.

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Summary

Poll

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

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