Category Chemistry

Sonar uses ultrasonic sounds to find out where and how far away something is. This is called echo-location. The sounds are transmitted and bounced back by the object. The time that passes between the transmission and the reception of the reflected sound tells how far away the object is. Sonar is used particularly at sea to establish the depth of water beneath a boat.

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. NOAA scientists primarily use sonar to develop nautical charts, locate underwater hazards to navigation, search for and map objects on the seafloor such as shipwrecks, and map the seafloor itself. There are two types of sonar—active and passive.

Active sonar transducers emit an acoustic signal or pulse of sound into the water. If an object is in the path of the sound pulse, the sound bounces off the object and returns an “echo” to the sonar transducer. If the transducer is equipped with the ability to receive signals, it measures the strength of the signal. By determining the time between the emission of the sound pulse and its reception, the transducer can determine the range and orientation of the object.

Passive sonar systems are used primarily to detect noise from marine objects (such as submarines or ships) and marine animals like whales. Unlike active sonar, passive sonar does not emit its own signal, which is an advantage for military vessels that do not want to be found or for scientific missions that concentrate on quietly “listening” to the ocean. Rather, it only detects sound waves coming towards it. Passive sonar cannot measure the range of an object unless it is used in conjunction with other passive listening devices. Multiple passive sonar devices may allow for triangulation of a sound source.

It’s a fact well-known enough to be the tagline to the 1979 sci-fi horror blockbuster Alien: “In space, no one can hear you scream.” Or to put it another way, sound can’t be carried in the empty vacuum of space – there just aren’t any molecules for the audio vibrations to move through. Well, that is true: but only up to a point.

As it turns out, space isn’t a complete and empty void, though large swathes of it are. The interstellar gas and dust left behind by old stars and sometimes used to create new ones does have the potential to carry sound waves – we just aren’t able to listen to them. The particles are so spread out, and the resulting sound waves are of such a low frequency, that they’re beyond the capabilities of human hearing.

As Kiona Smith-Strickland explains at Gizmodo, sounds travel as molecules bump into each other, the same way that ripples spread out when you drop a stone into a pond: as the ripples get farther and farther away, the sound gradually loses its force, which is why we can only hear sounds generated near to us. As a sound wave passes, it causes oscillations in the air pressure, and the time between these oscillations represents the frequency of the sound (measured in Hertz); the distance between the oscillating peaks is the wavelength.

If the distance between the air particles is greater than this wavelength, the sound can’t bridge the gap and the ‘ripples’ stop. Therefore, sounds have to have a wide wavelength – which would come across as a low pitch to our ears – in order to make it from one particle to the next out in certain parts of space. Once sounds go below 20 Hz, they become infrasound’s, and we can’t hear them.

One example noted by Gizmodo is of a black hole, which emanates the lowest note scientists know about so far: it’s about 57 octaves below middle C and well below our hearing range (about a million billion times deeper than the sounds we can hear). You’d expect to be able to measure about one oscillation every 10 million years in a black hole sound, whereas our ears stop short with sounds that oscillate 20 times per second.

Back on our own planet, the sounds of very strong earthquakes are sometimes intense enough to make it out into space, and infrasound can carry on going where normal sound has to pull up.

For a short amount of time after the Big Bang (about 760,000 years), the Universe was dense enough for normal sounds to pass through it. And if you hear the sound of a planet or spacecraft exploding in a Star Wars movie, remember that the filmmakers are taking liberties: chances are you wouldn’t hear much of it at all.

Garden and interior designers sometimes make use of a colour wheel. This helps them to choose colours that are in harmony with each other when that is appropriate. When a more striking effect is required, colours that contrast can be chosen. One half of the wheel has colours that give a warm feeling, while the other half has cooler hues.

A color wheel or color circle is an abstract illustrative organization of color hues around a circle, which shows the relationships between primary colors, secondary colors, tertiary colors etc.

Some sources use the terms color wheel and color circle interchangeably; however, one term or the other may be more prevalent in certain fields or certain versions as mentioned above. For instance, some reserve the term color wheel for mechanical rotating devices, such as color tops, filter wheels or Newton disc. Others classify various color wheels as color disc, color chart, and color scale varieties.

As an illustrative model, artists typically use red, yellow, and blue primaries (RYB color model) arranged at three equally spaced points around their color wheel. Printers and others who use modern subtractive color methods and terminology use magenta, yellow, and cyan as subtractive primaries, Intermediate and interior points of color wheels and circles represent color mixtures. In a paint or subtractive color wheel, the “center of gravity” is usually (but not always) black, representing all colors of light being absorbed; in a color circle, on the other hand, the center is white or gray, indicating a mixture of different wavelengths of light (all wavelengths, or two complementary colors, for example).

The original color circle of Isaac Newton showed only the spectral hues and was provided to illustrate a rule for the color of mixtures of lights, that these could be approximately predicted from the center of gravity of the numbers of “rays” of each spectral color present. The divisions of Newton’s circle are of unequal size, being based on the intervals of a Dorian musical scale. Later color circles include the purples, however, between red and violet, and have equal-sized hue divisions. Color scientists and psychologists often use the additive primaries, red, green and blue; and often refer to their arrangement around a circle as a color circle as opposed to a color wheel.

Water is said to be “hard” when it has certain minerals dissolved in it. The most noticeable effect of hard water is that soap does not lather well in it, instead forming a kind of scum. There are two kinds of water hardness, depending on which chemicals are dissolved in it. Temporary hardness can be removed by boiling the water. The chemicals become a solid, which is the scale that sometimes furs up kettles and shower heads. Permanent hardness can be removed by using a water softener, which exchanges the calcium and magnesium ions that cause the hardness with sodium ions.

Hard water (or water hardness) is a common quality of water which contains dissolved compounds of calcium and magnesium and, sometimes, other divalent and trivalent metallic elements.

The term hardness was originally applied to waters that were hard to wash in, referring to the soap wasting properties of hard water. Hardness prevents soap from lathering by causing the development of an insoluble curdy precipitate in the water; hardness typically causes the buildup of hardness scale (such as seen in cooking pans). Dissolved calcium and magnesium salts are primarily responsible for most scaling in pipes and water heaters and cause numerous problems in laundry, kitchen, and bath. Hardness is usually expressed in grains per gallon (or ppm) as calcium carbonate equivalent.

Oils and fats do not mix with water, so washing greasy clothes or hair in water alone will not clean them. Soap contains ions that are attracted to water at one end and to grease at the other. This end of each ion attaches itself to the grease, while the other end, attracted to the water, pulls the grease away from the fabric or hair. Hard water is a problem because the ions react with the chemicals in the water to form scum.

Evaporation is another way of separating water from chemicals dissolved in it. It works in the same way as distillation, except that evaporation is usually used when it is the substances in the water that are needed, not the water itself. The water is usually allowed to drift away as steam. In other words, distillation is used to obtain the solvent, while evaporation is used to obtain the solute.

Evaporation happens when a liquid turns into a gas. It can be easily visualized when rain puddles “disappear” on a hot day or when wet clothes dry in the sun. In these examples, the liquid water is not actually vanishing—it is evaporating into a gas, called water vapor.

Evaporation happens on a global scale. Alongside condensation and precipitation, evaporation is one of the three main steps in the Earth’s water cycle. Evaporation accounts for 90 percent of the moisture in the Earth’s atmosphere; the other 10 percent is due to plant transpiration.

Substances can exist in three main states: solid, liquid, and gas. Evaporation is just one way a substance, like water, can change between these states. Melting and freezing are two other ways. When liquid water reaches a low enough temperature, it freezes and becomes a solid—ice. When solid water is exposed to enough heat, it will melt and return to a liquid. As that liquid water is further heated, it evaporates and becomes a gas—water vapor.

These changes between states (melting, freezing, and evaporating) happen because as the temperature either increases or decreases, the molecules in a substance begin to speed up or slow down. In a solid, the molecules are tightly packed and only vibrate against each other. In a liquid, the molecules move freely, but stay close together. In a gas, they move around wildly and have a great deal of space between them.

In the water cycle, evaporation occurs when sunlight warms the surface of the water. The heat from the sun makes the water molecules move faster and faster, until they move so fast they escape as a gas. Once evaporated, a molecule of water vapor spends about ten days in the air.

As water vapor rises higher in the atmosphere, it begins to cool back down. When it is cool enough, the water vapor condenses and returns to liquid water. These water droplets eventually gather to form clouds and precipitation.

Evaporation from the oceans is vital to the production of fresh water. Because more than 70 percent of the Earth’s surface is covered by oceans, they are the major source of water in the atmosphere. When that water evaporates, the salt is left behind. The fresh-water vapor then condenses into clouds, many of which drift over land. Precipitation from those clouds fills lakes, rivers, and streams with fresh water.

Like all other living things, bacteria need water to survive and reproduce. If foods, such as pulses and cereals, are dried, most bacteria cannot attack them, so they are very slow to decay.

Food drying is one of the oldest methods of preserving food. Since drying reduces the moisture in foods making them lightweight and convenient to store, it can easily be used in place of other food preservation techniques. In fact, one can even use drying along with other food preservation techniques such as freezing or canning, which would make the process of food preservation even better.

 Drying food is simple, safe and easy to learn. The early American settlers practiced drying food using the natural forces of sun and wind and today, the use of technology has revolutionized this method of preserving food. With modern food dehydrators, foods such as fruit leathers, fruit chips, dried nuts and seeds and meat jerky, can all be dried year-round at home. Being easy to store and carry and requiring no refrigeration makes dried foods ideal for domestic use as well as for use in the rough outdoors.

Moreover, dried foods are good sources of quick energy and wholesome nutrition, since the only thing lost during preservation is moisture. For instance, meat jerky, dried nuts and seeds are good sources of protein for a snack or a meal. The fruit leathers and chips provide plenty of quick energy. Dried vegetables, too, can be used to prepare wholesome casseroles and soups and the nutritional value can be enhanced by using the soaking water for cooking. Therefore, dried foods are an easy food option for busy executives, hungry backpackers and active women and children, all of whom can benefit from the ease of use and nutritional content of dried foods.