A region in the deep ocean in which the speed of sound decreases to a minimum value with depth, and then increases in value as a result of pressure. The sound waves are focused by refraction by the waters above and below, and can travel thousands of kilometers in this zone. See sound channel.
Just as a microphone collects sound in the air, a hydrophone detects acoustic signals under the water. Most hydrophones are based on a special property of certain ceramics that produces a small electrical current when subjected to changes in underwater pressure.
Chemical and physical properties of seawaterThe six most abundant ions of seawater are chloride (Cl−), sodium (Na+), sulfate (SO24−), magnesium (Mg2+), calcium (Ca2+), and potassium (K+). By weight these ions make up about 99 percent of all sea salts.
about 35 parts per thousand
But underwater, humans don't hear using the normal channels. Instead, the study found that humans hear through bone conduction, which bypasses the outer ear and the ossicles of the middle ear. Instead, sound comes through the mastoid, or the bone you can feel if you put your fingers behind the ear.
The temperature effects dominate at the surface, so the speed of sound is fast in surface waters. As depth increases, the temperature and the speed of sound decline. Near the bottom, the extreme pressure dominates, and even though temperatures are low, the speed of sound increases with depth.
Sound travels faster in water than in air. The speed of sound in air under typical conditions is about 343 meters per second, while the speed of sound in water is about 1,480 meters per second. Fundamentally, standard sound is a compression wave traveling though a material.
Temperature and Speed of SoundAt a lower temperature, particles of the medium are moving more slowly, so it takes them longer to transfer the energy of the sound waves.
Temperature is another condition that affects the speed of sound. Heat, like sound, is a form of kinetic energy. Molecules at higher temperatures have more energy and can vibrate faster and allow sound waves to travel more quickly. The speed of sound at room temperature air is 346 meters per second.
As a rule sound travels slowest through gases, faster through liquids, and fastest through solids. The speed of light as it travels through air and space is much faster than that of sound; it travels at 300 million meters per second or 273,400 miles per hour.
Therefore, sound travels faster at higher temperatures and slower at lower temperatures. Solids are much more elastic than liquids or gases, and allow sound waves to travel through them very quickly, at about 6000 feet per second.
At a constant temperature, the gas pressure has no effect on the speed of sound, since the density will increase, and since pressure and density (also proportional to pressure) have equal but opposite effects on the speed of sound, and the two contributions cancel out exactly.
Sonar uses sound waves to 'see' in the water.Sonar, short for Sound Navigation and Ranging, is helpful for exploring and mapping the ocean because sound waves travel farther in the water than do radar and light waves.
Bubbles scatter underwater sound, causing its speed to slow. Low frequency (low-pitched) sounds travel slower than high frequency (high-pitched) sounds. The amount of scattering is affected by the size of the object (in this case, the bubbles) and the wavelength of the sound.
While sound moves at a much faster speed in the water than in air , the distance that sound waves travel is primarily dependent upon ocean temperature and pressure.
: an instrument for listening to sound transmitted through water.
A sonar device sends pulses of sound waves down through the water. When these pulses hit objects like fish, vegetation or the bottom, they are reflected back to the surface. The sonar device measures how long it takes for the sound wave to travel down, hit an object and then bounce back up.
It is sometimes referred to as the midnight zone or the dark zone. This zone extends from 1,000 meters (3,281 feet) down to 4,000 meters (13,124 feet). Here the only visible light is that produced by the creatures themselves. The water pressure at this depth is immense, reaching 5,850 pounds per square inch.
Cards In This Set
| Front | Back |
|---|
| Which method best transmits heat through water? | Convection |
| Which substance has the greatest density | Cold salt water |
| If the salinity of ocean water is 36%, there are ____ g of salt left from evaporating 2kg of seawater | 72 |
| Ions are removed from seawater by | Adsorption |
The salinity of seawater is defined as the total amount by weight of dissolved salts in one kilogram of seawater. Salinity is expressed in the unit g / kg, which is often written as ppt (part per thousand) or ‰ (permil). According to the practical salinity scale, typical 'standard' seawater has a salinity of 35.
Depth finder, also called echo sounder, device used on ships to determine the depth of water by measuring the time it takes a sound (sonic pulse) produced just below the water surface to return, or echo, from the bottom of the body of water.
On a cold day, there tends to be a layer of warmer air above the cold pockets closest to the ground. Because sound moves faster in warm air than colder air, the wave bends away from the warm air and back toward the ground. That's why sound is able to travel farther in chilly weather.
While typically not rigorously reliable, various body dimensions can be used underwater for crude estimates of distance. The most common involves the thumb ( from first knuckle to tip; approximately 1 inch), out-stretched hand (6-10 inches), out-stretched arms (tip-to-tip approximately body height ).
The acoustic thermometer works by transmitting sound waves along a gas-filled tube from a speaker at one end to a microphone at the other. By measuring the amount of time it takes the sound waves to travel along the tube, the temperature can be calculated.
But the critical factor in the speed of sound in water is actually the temperature—the higher temperature of the molecules creates a medium that allows sound to travel faster. Keeping salinity and pressure constant, sound travels about 15 feet per second faster for every 1.8 degree Fahrenheit rise in temperature.
Acoustic thermometry is an idea to observe the world's ocean basins, and the ocean climate in particular, using trans-basin acoustic transmissions. "Thermometry", rather than "tomography", has been used to indicate basin-scale or global scale measurements.
