Sound:
Longitudinal Waves
Sound waves make air vibrate . The vibrations in the air make your eardrum
vibrate so you can hear.
For sound to be heard vibrations must have matter to travel through.
You can’t hear sound in outer space because there is no matter/air to carry the vibrations.
*Bell jar video on website: example of sound in a vacuum.
Question: How are astronauts able to talk to each other in space????They communicate through radio waves .
There are 3 states of matter through which sound can travel: solids, liquids, and gases. The speed with which a sound travel depends upon the medium through which it travels.
solid Particles are close together
fastest
liquids Particles are farther apart
Not as fast
gases Particles are very far apart
slowest
Examples: If you put your ear on steel train tracks you can hear the train coming faster than you could hear it through air.Dolphins can communicate more quickly under water than through air.
Loudness/Volume: Volume is loudness or softness. Loud sounds use a lot of energy. Soft sounds use little energy. Example: The harder a drum is hit,
the more an object vibrates. The more an object vibrates the louder the sound it makes.
Wave characteristic that impacts loudness:Loudness= Amplitude/Intensity/Energy
Higher amplitude= Louder Lower amplitude= Softer
Decibels : unit used to measure the intensity or loudness of a sound
Pitch:
Pitch is the highest or lowest sound an object makes.
Objects that vibrate slowly make a low pitch. Ex: drum
Objects that vibrate quickly make a high pitch. Ex: recorder/flute
Wave characteristic that impacts pitch is
Frequency.
The higher the frequency the higher the pitch.
The lower the frequency the lower the pitch.
Low pitch High pitch
Low frequency High frequency
Long wavelength short wavelength
Real world application to music:
Guitar strings
High pitch Low pitchtight looseshort long
Thin thick
Organ Pipes
High pitch Low pitch short long
*Tube demo
Doppler Effect: video on websiteAn increase or decrease in the frequency of sound as the source and observer move toward or away from each other causes a sudden change in pitch like in a passing siren.
Why does this happen?
When a fire truck approaches the pitch sounds higher because the waves arrive more quickly .
When a fire truck moves away you hear a drop in pitch because the waves arrive less frequently .
Higher pitch Lower pitchShorter wavelength Longer wavelengthMore frequent Less frequent
Question: When a source moves toward you is there an increase or decrease in frequency? Explain. Frequency increases
because the wavelengths get closer together.
Review:
Sound is a kind of energy that can be heard.
A sound is made when things vibrate. Amplitude/Volume is how loud or
soft a sound is. Pitch is how high or low a sound is.
TOD: Incorporating reading
Read page 542 – 543 in the text book and complete the following summary statement.
An echo is a sound wave that is ______________________.
You can hear someone talking in a different room through a doorway because sound waves are ___________.
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