Physics- Wave Motion and Sound

Why are sound waves mechanical?

-They cannot travel through a vacuum -their molecules vibrate back and forth from a fixed position -they must travel through a medium in which the molecules are alternately compressed and rarefied. -they travel in a straight line -they are longitudinal waves.

The nature of the molecules of the medium determines how well or rapidly the substance will carry the sound waves. What characteristics of the medium determine this?

1. The inertia of the molecules 2. The strength of the interaction -solids have molecules that are strongly attached so vibrations pass rapidly from molecule to molecule -thus, sound moves more rapidly through solids than through gases.

What is the frequency range for clinical imaging ultrasound?

1.0-15.0 MHz

What is a periodic motion?

A back and forth vibration that repeats itself.

What is a wave?

A disturbance that transfers energy from a source, but with no transference of matter.

What do sound waves require in order to travel?

A medium. Solid, liquid, or gas.

What is a longitudinal wave?

A wave in which particles of the medium move in a direction parallel to the direction that the wave moves.

What is a Transverse wave?

A wave in which particles of the medium move in a direction perpendicular to the direction that the wave moves.

In a room, the medium that the sound wave travels through is ___.

Air

How is wavelength measured on a longitudinal wave?

By measuring the distance between ant two corresponding points on adjacent waves. Typically, from one compression to the next compression or from one rarefaction to the next rarefaction.

What is compression?

Compression is a point in a medium through which a wave has increased density and pressure. Molecules are squeezed together.

What is the SI unit for frequency?

Cycles per second= Hertz (Hz); Kilohertz (kHz); Megahertz (MHz)

Period (T) and wavelength (λ) are ________ related.

Directly. They measure the same area on a wave but in different units of measurement. (Time vs. length)

What is the difference between frequency (f) and Period (T)?

Frequency (f) refers to hoe often something happens; it is a rate quantity. Frequency is the cycles per second. Period (T) refers to the time it takes something to happen; it is a time quantity. Period is the seconds per cycle.

What is the formula for frequency?

Frequency=velocity ÷ wavelength f= v/ λ

A high energy wave is characterized by ____ amplitude.

High

What is a medium?

It is the substance or material through which a wave travels.

A low energy wave is characterized by ___ amplitude.

Low

In a given medium, frequency and wavelength are inversely related. Thus, the _____ the frequency, the ______ the wavelength.

Lower, longer

In a 'stadium wave', what is the medium?

People

What is rarefaction?

Rarefaction is a point in a medium through which the wave has decreased density and pressure. Molecules are stretched apart.

Does sound travel faster through solids or gases?

Solids

What type of wave is sound?

Sound is ONLY ever a longitudinal, mechanical wave.

What is the formula for Period (T)?

T=1/f OR f= 1/T

What is the wavelength of a Transverse wave measured by?

The distance from crest to crest or trough to trough.

What is the medium in ultrasound?

The human body

What is a wavelength? (λ)

The length of one complete wave cycle. -Has a repeating pattern. -wavelength determined by both the source and the medium.

Define amplitude:

The maximum amount of displacement of a particle through the medium from its equilibrium, either positive or negative (crest or trough) The amplitude of the wave is related to the amount of energy carried by a wave.

What is frequency?

The number of cycles that occur in a specific duration of time. It is a rate! -A complete cycle is one crest and one trough. -in ultrasound, a wave's frequency is the number of cycles that occur in one second.

What happens when you increase the transducer frequency while doing an ultrasound?

The penetration capability is decreased but the image quality (resolution) is increased.

What happens when you decrease the transducer frequency while doing an ultrasound?

The penetration capability is increased but the image quality (resolution) is decreased.

Is the Period (T) determined by the sound source (transducer) or the medium it travels through?

The sound source

What is a Period (T)?

The time is takes to complete one cycle. (Seconds per cycle)

What is the source in ultrasound?

The transducer/Ultrasound machine

What is simple harmonic motion?

The vibratory motion that occurs when there is a restoring net force opposite to and proportional to the displacement.

True or false? Soundwaves are considered mechanical.

True

True or false: Air temperature affects how fast sound travels.

True. Sound waves travel faster in warmer temperatures because they are carried faster.

In a water wave, the medium that the wave travels through is _____.

Water

What is the only parameter determined by both the source and the medium?

Wavelength (λ)

What is equilibrium position?

When an object has not been disturbed; there is no force applied to the mass.

What are the units for wavelength (λ)?

mm or meters