PS.6 waves are important in the movement of energy. Key concepts include

1. energy may be transferred in the form of longitudinal and transverse waves
2. mechanical waves need a medium to transfer energy;
3. waves can interact
4. energy associated with waves has many applications

ENERGY MAY BE TRANSFERRED IN THE FORM OF LONGITUDINAL AND TRANSVERSE WAVES

Waves transmit energy from one place to another without a permanent transfer of mass.

• One wavelength is measured from any point on a wave to the corresponding point on the next wave.

• The amplitude of a wave depends on the type of wave and will be described for two types below.
  • As the energy carried by a wave increases, the amplitude of the wave increases.
• Wave frequency is number of waves produced over a given period.
  • There is an inverse relationship between frequency and wavelength.
  • As the frequency of a wave increases, wavelength decreases.
  • A wave with a higher frequency (shorter wavelength) carries more energy than a wave with a lower frequency (longer wavelength).
• The speed of a wave is defined as the distance a point on a wave travels over time.
  • It is expressed in units of meters/second (m/s).
• Waves can reflect, refract, and diffract.
  • Refraction occurs when a wave passes through different materials, resulting in a change in the speed of the wave.
  • Reflection occurs when a wave bounces from a surface back toward its source .
  • Diffraction is a characteristic of all wave types and occurs when a wave encounters irregular surfaces. 
    • This causes the waves to change direction and be scattered.
    • Diffraction is the bending of longitudinal waves around small obstacles or the spreading out of waves beyond openings.

Transverse Waves

• When energy passes through a medium (matter) in a transverse wave, particles vibrate in an up-and-down motion.
  • The particles move across, or at right angles to, the direction the wave is going.
  • A wave moving on a rope is an example of a transverse wave.
• Radiant energy travels in transverse waves .

• A wavelength on a transverse wave is the distance from one point to the next corresponding point (e.g., from the tip of one crest to the tip of the next crest) .
• The amplitude of a transverse wave is the distance from the rest position to the crest of a wave or to the trough of a wave.
  • It is the maximum distance the particles of a medium vibrate from their rest position.
  
  • A wave with a high amplitude carries more energy than a wave with a small amplitude carries .

Longitudinal (Compression) Waves

• Longitudinal waves are caused by vibrations carried through a substance, sometimes referred to as a medium (solid, liquid. or gas).
  • When energy is being transferred through a medium by a longitudinal wave, the particles of the medium vibrate back and forth along the same path that the wave travels.
  • The particles in a longitudinal wave do not move along the wave—only energy travels from one place to another.

• A compression (longitudinal) wave consists of a repeating pattern of compressions and rarefactions. 
  •  Wavelength is measured as the distance from one compression to the next compression . 
  •  The amplitude of a longitudinal wave is the largest distance the particles vibrate from their rest (starting) positions. 
  •  A wave with greater amplitude carries more energy. 
  •  For example, a longitudinal sound wave with greater amplitude will be louder than one with less amplitude .

MECHANICAL WAVES NEED A MEDIUM TO TRANSFER ENERGY

Mechanical waves (also called compression or longitudinal waves) are caused by vibrations carried through a substance, sometimes referred to as a medium (solid, liquid. or gas).

• When energy is being transferred through a medium by a longitudinal wave, the particles of the medium vibrate back and forth along the same path that the wave travels
  • vocal chords of a person,
  • the vibrating string and sound board of a guitar or violin,
  
  • the vibrating prongs of a tuning fork, or
  • the vibrating diaphragm of a radio speaker.
• The speed of a longitudinal wave depends on several factors, including the medium through which it travels.
  • For example, the speed of sound is slowest in a gas, faster in liquids, and fastest in solids. 
  •  Sound does not go through empty space (a vacuum).
  • Temperature also affects the speed of a longitudinal wave. 
  • For example, the warmer the medium, the faster sound travels .
• Sound, a form of mechanical energy, is propagated through longitudinal waves and needs a medium through which it is transmitted.
  • Sound is caused when something vibrates, making particles vibrate back and forth in the direction of the wave.
  • Loudness (of sounds) is related to the amplitude of the mechanical wave.
    • Greater amplitudes equate with louder sounds.
  • Pitch (of sounds) is related to the frequency of the mechanical wave.
    • Higher frequencies equate with higher pitches .

WAVES CAN INTERACT

Interference is the addition of two or more waves, resulting in a new wave pattern.

• Interference can be constructive or destructive.
• Waves of the same type that encounter each other pass through each other and exhibit interference .

Resonance is the tendency of a system to vibrate at maximum amplitude at certain frequencies.

• For instance, when several musical instruments of the same kind play the same notes, the waves may combine to produce a louder sound.

ENERGY ASSOCIATED WITH WAVES HAS MANY APPLICATIONS

Wave-based technology has many applications.

• Examples include (but are not limited to)
  • sonar
  • ultrasonography
  • vehicle parking sensors
  • wave power generators.

• model a compression (longitudinal) wave and diagram, label, and describe the basic components: wavelength, compression, rarefaction, and frequency.