SOL 5.2 a, b, c, d March 2013
Sound Notes
· Sound is a form of energy produced and transmitted by vibrating matter.
· Sound waves are compression (longitudinal) waves.
· When compression (longitudinal) waves move through matter (solid, liquid, or a gas), the molecules of the matter move backward and forward in the direction in which the wave is traveling.
· All sound energy is produced by vibrations. Vibrations are the back and forth motions of objects.
· All sound moves through matter (solid, liquid, gas). Sound cannot move through a vacuum, because there are no molecules to vibrate back and forth.
· The strengthening of a sound wave is called resonance.
· Sound travels in compression waves.
· As sound waves travel, molecules are pressed together in some parts, called Compression and in some parts are spread out, called rarefaction. Think of a slinky pressed together (compressions) and then spread apart (rarefactions).
· Sound waves have different parts. The top of a sound wave is called the crest, the bottom of a sound wave is called the trough, and the distance between two side by side crests is called the wavelength.
· When an object vibrates very quickly, the number of vibrations per minute increase and the sound becomes higher. When this same object vibrates more slowly, the number of vibrations per minute decrease, and the sound becomes lower.
· The frequency of sound is the number of wavelengths in a given unit of time.
· The highness and lowness of a sound wave is its pitch. Pitch is determined by the frequency of a vibrating object. Objects vibrating faster have a higher pitch than objects vibrating slower.
· Longer, larger objects (trombone) tend to vibrate slower than shorter, smaller objects (flute).
· Amplitude is the amount of energy in a compression (longitudinal) wave and is related to intensity and volume. For example, when a loud sound is heard, it is because many molecules have been vibrated with much force. A soft sound is made with fewer molecules being vibrated with less force.
· The speed of a sound depends on the kind of matter it is moving through.
· Of the three states of matter (gas, liquid, and solid) sound waves travel the slowest through gases, faster through liquids, and fastest through solids.
· In a gas the molecules are spaced very far apart. For sound to travel through air, the floating molecules of matter must vibrate and collide to form compression waves. Because the molecules of matter in a gas are spaced far apart, sound does not move very quickly through them.
· Sound travels faster in liquids than in gases because molecules are packed more closely together. This means that when the water molecules begin to vibrate they quickly begin to collide with each other forming a rapidly moving compression wave. Sound travels over four times faster than in air!
· Sound travels fastest through solids. This is because molecules in a solid are packed against each other. When a vibration begins, the molecules of a solid immediately collide and the compression wave travels rapidly. How rapidly, you ask? Sound waves travel over 17 times faster through steel than through air.
· As humans, we move air from our lungs across our vocal chords to produce sound waves. These sound waves create the sound we know as the human voice. Many animals like dogs and bats also create sounds in this way. However, marine mammals like whales pass air through air sacks located in their heads to create sounds.
· Hearing is the detection of sound.
· Sonar is a type of device used to detect sound. Ships use sonar to help them navigate their vessels, explore underwater areas of the ocean, and to find food.
· Some animals, such as bats and whales, used echolocation to help them find food, or even to escape predators.
· All animals detect sound differently because different animals are able to hear different frequencies of sound.
· As humans, our hearing is adapted to hear best the sounds we use every day.
· Because animals can hear sounds at different frequencies, some animals can hear sounds that humans can’t.