Sound



Sound Sound is energy moving in waves—sound is energy vibrating through substances.All sounds are caused by vibrations—the back and forth motion of molecules.Energy is needed to start an object vibrating to make sound.You can clap, pluck, blow, hit, or move something in many ways to make vibrations.Sound waves carry energy. That is because the energy that starts something vibrating is carried by the sound produced.A vibrating object makes many sound waves that move away from it in all directions.A sound wave is vibrating particles in areas of crowded particles followed by widely spaced particles that travel in waves.The sounds that you hear are usually moving through air. When a sound wave moves through air, the air molecules vibrate back and forth in the same direction as the sound. The vibrations push the air molecules close together, then pull them apart. These waves are called longitudinal waves. Longitudinal waves move in the same direction as the force making them.The part of a longitudinal wave in which the molecules are squeezed together is called a compression. The molecules are compressed, or squeezed together into a smaller space.The part of a longitudinal wave in which the molecules are pulled apart is called a rarefaction. There are the same number of molecules as in compression, but they are farther apart. How Does Sound Travel Through Different Materials?Sound needs matter to travel through—without matter, sound cannot travel.Sound does not travel through outer space because there are no particles of air to carry it along.Sound travels through air, of course.Sound travels through solids, liquids and gases.Sound travels at different speeds in different substances.Sound travels slowest in a gas.Sound travels faster in a liquid.Sound travels fastest through a solid.Sometimes sound waves bounce off surfaces and cause the sound to repeat—this is called an echo.Why Aren’t All Sounds the Same?The three features of sound are wavelength, frequency and amplitude.All sounds do not sound the same because they have different wavelengths, frequencies and amplitudes. WavelengthLike all waves, a sound wave has a certain wavelength. One wavelength is the distance from one area of squeezed particles to the next area of squeezed particles.FrequencyFrequency is the number of times a sound source vibrates in one second. The more wavelengths, the higher the frequency.Objects that vibrate quickly have a high frequency.Tightening and loosening guitar strings changes their frequency.Frequency determines pitch.Pitch is the highness or lowness of sound.Examples of sounds with a high frequency or pitch:a cat meowing, brakes squealing, emergency sirens, and a whistle blowingExamples of sounds with a low frequency or pitch:A book falling off a table, thunder, and a truck rumbling down the roadAmplitudeThe energy in a sound wave is called amplitude.Sounds with high amplitude are made by objects that vibrate with a lot of energy. Amplitude is the loudness of sound.The louder a sound is, the higher its amplitude. The higher the amplitude of a sound wave, the more energy it has.As a rocket blasts off, high-amplitude sound waves fill the air.Whispering makes sound waves of very low amplitude.Sounds with a high amplitude:fireworks, thunder, emergency sirens, and fog hornsSounds with a low amplitude:a sigh or the rustle of leavesThe amplitude of a wave depends on its size—the height of a wave from its crest to its trough.The crest is the highest point of the wave: the trough is the lowest point. ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download