sound waves

Sound is created when something vibrates, sending waves through the air or other media.

A vibrating object causes the surrounding molecules to also move. This disturbance travels through the medium (solids, liquids, and gases) until it reaches our ears.

The vibrations of the guitar strings, when plucked, create a sound.

The vibrations produced in the person’s vocal cords travel as sound waves.

How do sounds travel?

Sound travels through different mediums as longitudinal waves.

The particles of the medium move back and forth parallel to the direction the wave is traveling. 

DIRECTION OF WAVE TRAVEL

Moving the springy toy back and forth demonstrates how particles vibrate to produce longitudinal waves.

How do sounds travel?

This movement creates areas of compression, where particles are closer together, and rarefaction, where they are spread apart.

Why can’t sound travel through outer space?Medium

Sound waves must have a medium to travel through

• Gas

• Liquid

• Solid

In outer space, there are no molecules to compress or rarefy, so sound cannot travel

Speed of Sound

Speed of sound depends on the physical properties of the medium it travels through

• Elasticity

• Density

• Temperature

At room temperature, sound waves travel through air at about 342 m/s

Looking at the table above, through which medium does sound travel the fastest? Slowest?

Physical Properties of Media - Elasticity

Elasticity - the ability of a material to bounce back after being disturbed

Solid materials are usually more elastic than liquids and gases

Particles in solids do not move very far, so they bounce back and forth quickly as the vibration travels through the object, which allows waves to move faster

Physical Properties of Media - Density

Density - how much matter there is in a given amount of space

The speed of sound depends on how close together the particles of the substance are in the medium

• Closer together = faster movementPhysical Properties of Media - Temperature

  
  

  Temperature - degree or intensity of heat present in a substance or object

  
  

  In a given medium (S, L, G), sound travels more slowly at lower temperatures

  • Increasing temperature allows for particles to move faster

  • Faster movement = faster speed of soundProperties of Sound Waves

    
    

    4 properties of sound waves:

    • Intensity

    • Loudness

    • Frequency

    • Pitch

    
    

    Even though sound waves are longitudinal waves, it is easier to visualize the properties as transverse waves

    
    Properties of Sound Waves - INTENSITY

    
    

    Intensity - the amount of energy the wave carries per second through a unit of area

    
    

    Amplitude increases with increased energy

    
    

    Measured in watts per square meter (W/m2)

    
    

    For both graphs above, give an example of real life sounds that could make the two graphs.Properties of Sound Waves - LOUDNESS

    
    

    Loudness - what you actually hear

    
    

    Though not the same as intensity, the greater the intensity of a sound wave, the louder it is

    
    

    Measured in decibels (dB)

    Maximum safe level is 85 dB 

    
    

    Name two sounds that are not safe for human ears for prolonged periods of time.

    
    Properties of Sound Waves - FREQUENCY

    
    

    Frequency - the number of vibrations that occur per second

    
    

    Wavelength changes with frequency

    • Lower frequency = longer wavelength

    
    

    Measured in Hertz (Hz) 

    
    

    Which color wave has the greatest frequency?

    
    Properties of Sound Waves - PITCH

    
    

    Pitch - a description of how high or low the sound seems to a person

    
    

    High frequency = high pitch

    
    

    Low frequency = low pitch

    
    Doppler Effect

    
    

    The apparent change in frequency as a wave source moves in relation to the listener

    
    

    TOWARD listener 

    • Waves are at a higher frequency, so pitch appears to increase (high)

    
    

    AWAY from listener

    • Waves are at a lower frequency, so pitch appears to decrease (low)