Waves and Sound Concepts Quiz

Waves and Sound

•  Waves transfer energy from one place to another.
•  Waves are rhythmic disturbances that carry energy.
•  Examples include: water waves, microwaves, sound waves, and radio waves.
•  Water waves transfer energy through water, and earthquakes transfer energy through Earth.

Characteristics of Waves

•  Waves travel through a medium, which is a material.
•  Examples of mediums include solids, liquids, and gases.
•  Mechanical waves require a medium to travel.
•  Electromagnetic waves, such as light, do not need a medium.

Types of Waves

•  Transverse waves: The medium moves at right angles to the direction of the wave.
  • Examples include water waves and light waves.
•  Compressional (Longitudinal) waves: The medium vibrates in the same direction as the wave.
  • Examples include sound waves and ultrasounds.

Measuring Transverse Waves

•  Crest: The highest point on a wave.
•  Trough: The lowest point on a wave.
•  Wavelength: The distance between one point on a wave and the identical point on the next wave (measured from crest to crest).
•  Amplitude: The distance from the crest of a wave to the rest position of the medium. Larger amplitude = more energy.

Wave Frequency

•  Frequency is the number of wave crests that pass one place each second.
•  Frequency is measured in Hertz (Hz).
•  1 Hz = 1 wave per second.
• As frequency increases, wavelength decreases.

Wave Velocity

•  Wave velocity (v) is how fast a wave moves.
•  Wave velocity is calculated by multiplying wavelength and frequency.
•  Wavelength is represented by the Greek letter lambda (λ).

Calculating Wave Velocity

• Wave speed = wavelength × frequency
• v = λ × f

Sound Waves

•  Molecules in the air vibrate, creating compressions and rarefactions, which are the characteristic patterns of sound waves.
•  Pitch is related to the frequency of sound. Higher frequency = higher pitch.

Pitch

•  Bats use ultrasonic sound to locate objects and hunt.
•  Elephants use infrasound to communicate over long distances.
•  Infrasound has too low a frequency for humans to hear.

Doppler Effect

•  The frequency of sound changes as the source or observer moves toward or away from each other.
•  This change in frequency causes the sudden change in pitch heard in a passing siren.

Speed of Sound

•  The speed of sound depends on the material of the vibrating medium.
•  Sound travels faster in solids, then liquids, then gases.
•  Sound travels faster in warm air, and slower in cold air.

Wave Reflection

•  Sound waves can reflect off of surfaces, creating echoes.
•  Smooth, hard surfaces reflect sound best.
•  Rough, soft surfaces reflect sound poorly.
• The law of reflection states that the angle of incidence equals the angle of reflection.

Wave Refraction

•  Waves bend when traveling through a medium with changing characteristics (density or temperature).
•  Examples include light bending from air to water, or sound bending through air at different temperatures.

Acoustics

•  Acoustics is the study of sound and how it interacts with its environment.
•  Acoustics plays a role in designing concert halls, theaters, and other buildings to enhance sound quality.

Interference

•  Waves can combine and form a new wave.
•  Constructive interference: Compressions of waves overlap to make the sound louder.
•  Destructive interference: A compression of a wave overlaps with the rarefaction (opposite movement) of another wave to decrease the loudness and possibly cancel the sound.

Natural Frequencies

•  Stringed instruments vibrate at their natural frequencies when plucked. 
•  This vibration is a forced vibration, causing the air to vibrate more and producing a larger sound.

Resonance

• When the forced vibration matches a natural frequency, it can increase the amplitude
• Examples include: swinging on a swing set, or the Tacoma Narrows bridge collapse.
• Soldiers are told to break step when marching across bridges to prevent rhythmic matching that causes excessive vibrations.

Noise vs. Music

• Noise has no set pattern and no definite pitch.
• White noise has all frequencies in equal amplitude.
• Music is characterized by specific pitches (frequencies) and regular patterns.

Musical Sounds

• The quality of a sound depends on the combination of frequencies that create the sound.
• Instruments create different combinations of frequencies, which is why instruments sound different even if they play the same note at the same volume.

Reverberation

• Reverberation is the effect produced by repeated reflections of sound.