Ms. Barlow’s 8th Grade Physical Science Class The Nature of Sound Ms. Barlow’s 8th Grade Physical Science Class

GPS S8P4. Students will explore the wave nature of sound and electromagnetic radiation. d. Describe how the behavior of waves is affected by medium (such as air, water, solids). e. Relate the properties of sound to everyday experiences.

Sound Waves Sound travels in the form of waves. Sound waves are longitudinal or compression waves. Example: A vibrating guitar string forces surrounding air molecules to be compressed and expanded. This creates a pressure disturbance consisting of an alternating pattern of compressions and rarefactions.

Moving Through Mediums Sound waves can travel through any type of medium – solid, liquid, or gas. The speed of a sound wave through a medium depends on the substance the medium is made of and whether it is solid, liquid, or gas.

Sound travels faster in solids (fastest) and liquids than in gases because the individual molecules in a liquid or solid are closer together than the molecules in a gas. Speed of sound does not depend on the loudness of the sound Sound also travels faster in increased temperatures.

Sound travels more slowly in denser mediums. Sound travels in more quickly in mediums that have a high degree of elasticity. Elasticity: the ability of a material to bounce back after being disturbed.

Properties of Sound Intensity and loudness Frequency and pitch The Doppler Affect

The Intensity of Sound Intensity is the amount of energy that flows through a certain area in a specific amount of time. When you turn down the volume of your radio, you reduce the energy carried by the sound waves, so you also reduce their intensity. Intensity also influences how far away a sound can be heard.

The intensity of a sound wave is measured in Watts/meter2. The greater the amplitude, the greater the rate at which energy is transported through it, and the more intense that the sound wave is. The intensity of a sound wave is measured in Watts/meter2.

The intensity of a sound wave is measured in Watts/meter2. Loudness is the human perception of sound intensity. Sound waves with high intensity carry more energy. A sound wave of greater intensity generally sounds louder. Loudness is measured in decibels (dB)

Frequency and Pitch Frequency is the measure of how many wavelengths pass a particular point each second. Frequency is measured in Hz – 1 Hz means that one wavelength passes by in 1 s. Pitch is how high or low a sound seems to be. The pitch of a sound is related to the frequency of the sound waves.

As the frequency of a sound wave decreases, the pitch becomes lower. As the frequency of a sound wave increases, the pitch becomes higher.

Sound waves with frequencies above the normal human range of hearing are called Ultrasound. Sounds with frequencies below the normal human range of hearing are called infrasound.

The Doppler Effect The change in pitch or wave frequency due to a moving wave source is called Doppler effect. The Doppler effect occurs when the source of a sound wave is moving relative to a listener.

When the source of some wave is approaching you, the wave you received will be in a higher frequency (shorter wavelength) compared to the case when the source is stationary. If the source is leaving you, you will see lower-frequency wave (longer wavelength).

For sound waves this manifests itself as a rise in pitch (i. e For sound waves this manifests itself as a rise in pitch (i.e. frequency) for an approaching wave and a decrease in pitch for a receding wave. This is why we hear the siren of a police car change pitch as it passes us.

http://www.wfu.edu/physics/demolabs/demos/3/3b/3b40xxa.mpg