Sound

1. Sound by, Drew Harris

2. Vibrations Back and forth movements like “snapping a ruler” are vibrations. When you hum, you can feel vibrations by putting your fingers on your throat. Sound is vibrations you can hear. You can see and feel things vibrate, but not the sound in the air.

3. Sound Waves The area where sound is pushed together is a compression. As vibrations pull, they decrease the pressure in the air. This results in alternating areas of high and low pressure in the air. Sound waves are quickly moving areas of high and low pressure. All sound moves as sound waves. Sound moves in all directions from a vibrating object. Most sound we hear travels through air, but it can travel through all of the three states of matter.

4. Waves You throw a rock in a pond, and see the ripples in the water. The ripples represent sound waves. The greatest distance a water rises from its calm position is amplitude. The more energy a wave carries, the higher the amplitude. The distance between one ripple to another in a straight line is the wavelength. Peak Valley

5. Ripples in a pond Amplitude Wavelength

6. Waves and Sound The top and bottom part of a ripple traces a sound waves high and low pressure. The peak shows where pressure is highest, and the valley shows where it is lowest. The faster the source vibrates, the closer together the waves (peaks) will be. The amplitude (or tallness) of a wave stands for a louder sound.

7. Hearing and sound Loudness You can whisper and you can shout. Whispers are soft and shouting is loud. You can hear how soft or loud a sound is. This is called loudness. The amplitude of a sound wave shows how loud it is. We hear sound when sound reaches our ears. Our brains then process this and tell us what the sound is.

8. As well as making loud and soft sounds, you can also make high and low sounds. When you growl like a dog you make a low sound, when you squeak like a mouse you are making a high sound. A sound’s pitch is how high or low a sound is. Pitch depends on how fast the vibration. If it is fast, it is high; if it is slow, it is low. The longer the wavelength the lower the sound. Another way to make a different pitch is to change the thickness of the material that vibrates. A thin string vibrates faster than a thick string. Pitch

9. Speed of Sound Light moves faster than sound. The speed that a sound wave travels at is called the speed of sound. Sound travels fast through solids. Sound moves slower in liquids than in solids and slower in gases than liquids. Sound travels about one mile in five seconds in air. In some cases sound will bounce of objects. This is called an echo. You cannot hear all sound waves. If the surface is bumpy, the sound goes in all different directions, and makes it hard to hear it.

10. Sonic Booms Some jets and planes can fly faster than sound. Planes flying faster than sound make sound waves move in all directions. When the plane catches up to these sound waves, they become one strong wave called a shock wave. If the air wave goes straight, the plane pushes it and forces the air wave to go faster than normal. This causes a “boom-boom.” That is called a sonic boom.

11. Sound Review

12. Sound Vocabulary • sound – a series of vibrations that you can hear • compression – the part of a sound wave in which air is pushed together • sound wave – a moving pattern of high and low pressure that you can hear • amplitude – a measure of the strength of a sound wave; shown by height on a wave diagram • wavelength – the distance from one compression to the next in a sound wave • loudness – your perception of the amount of sound energy reaching your ear • pitch – a measure of how high or low a sound is • speed of sound – the speed at which a sound wave travels through a given material • echo – a sound reflection • sonic boom – a shock wave of compressed sound waves produced by an object moving faster than sound