What Is Glycerin

Glycerin is a thick liquid that is colorless and sweet tasting. It has a high boiling point and freezes to a paste. Glycerin's most common use is in soap and other beauty products like lotions, though it is also used, in the form of nitroglycerin, to create dynamite.

This liquid is popular in beauty products because it is a humectant — it absorbs ambient water. This means that it can help seal in moisture. Not only is it used in the soap making process, it's a byproduct too. Many soap manufacturers actually extract glycerin during the soap making process and reserve it for use in more expensive products. 

Even when soap manufacturers extract glycerin, however, some amount remains in every bar of soap. Additional may be added to a bar of soap in order to produce a clear finish and extra moisturizing qualities. The extra also enhances the cleaning aspect of soap.

Glycerin can be dissolved easily into alcohol and water but not into oils. The pure chemical element is called Glycerol, which indicates that it is an alcohol. The impure commercial product is called glycerin.

The fact that is also easily absorbs water from the surrounding air means that glycerin is hygroscopic. If you were to leave some in the open, it would absorb water from the surrounding air to eventually become 20% water and 80% glycerin. If you were to place a small amount of pure glycerin on your tongue, your tongue would blister because it is dehydrating. When beauty products containing glycerin are used on skin that is well moisturized, it can help keep that moisture in. Where we get glycerin has changed over time. In 1889, for example, commercial candlemaking was the only way to obtain glycerin. At that time, candles made from animal fat which served as the source of glycerin. Extraction is a complicated process and there are various ways of going about it. The simplest way is to mix fat with lye. When the two are mixed, soap is formed and glycerin is then removed. Still, a small amount of glycerin remains in the soap. Glycerin has a variety of uses. As stated above, it can be used to make dynamite. It is not explosive alone, however, and it has to be processed before it can be used as an explosive. It's also used in prints and inks, preserved fruits, lotions and as a lubricant. It can also be used to prevent hydraulic jacks from freezing. Its antiseptic qualities permit its use in the preservation of scientific specimens.

What is Gravity

Essentially, gravity is an attractive force between objects. Most people are familiar with gravity as the reason behind things staying on the Earth's surface, or "what goes up, must come down," but gravity actually has a much vaster significance. Gravity is responsible for the formation of our Earth and all other planets and for the movement of all heavenly bodies. It is gravity that makes our planet revolve around the Sun, and the Moon revolve around the Earth.

Though humans have always been aware of gravity, there have been many attempts to accurately explain it throughout the years, and theories must regularly be improved upon to account for previously unconsidered aspects of gravity. Aristotle was one of the first thinkers to postulate the reason for gravity, and his and other early theories relied on a geocentric model of the universe, with the Earth at its center. Galileo, the Italian physicist who made the first telescopic observations supporting a heliocentric model of the solar system, with the Sun at the center, also made strides in the theory of gravity around the turn of the 17th century. He discovered that objects of varying weights fall towards the Earth at the same speed. 

In 1687, English scientist Sir Isaac Newton published his law of universal gravitation, which is still used to describe the forces of gravity in most everyday contexts. Newton's first law states that the force of gravity between two masses is directly proportional to the product of the two masses and inversely proportional to the square of the distance between them, or mathematically: F=G(m₁m₂/d²), where G is a constant. 

Newton's second law states that gravitational force is equal to the product of a body's mass and its acceleration, or F=ma. This means that two masses that are gravitationally attracted to each other experience the same force, but that it translates into a much greater acceleration for a smaller object. Therefore, when an apple falls towards the Earth, both the Earth and the apple experience equal force, but the Earth accelerates towards the apple at a negligible speed, since it is so much more massive than the apple. 

Around the late 19th century, astronomers began to notice that Newton's law did not perfectly account for observed gravitational phenomena in our solar system, notably in the case of Mercury's orbit. Albert Einstein's theory of general relativity, published in 1915, resolved the issue of Mercury's orbit, but it has since been found to be incomplete as well, as it cannot account for phenomena described in quantum mechanics. String theory is one of the foremost modern theories to explain quantum gravity. Though Newton's law is not perfect, it is still widely used and taught because of its simplicity and close approximation of reality. 

Because gravitational force is proportional to the masses of the two objects experiencing it, different heavenly bodies exert stronger or weaker gravitational force. For this reason, an object will have different weights on different planets, being heavier on more massive planets and lighter on less massive planets. This is why humans are much lighter on the Moon than they are on the Earth.

It's a popular misconception that astronauts experience weightlessness during space travel because they are outside the field of gravitational force of a large body. In fact, weightlessness during space travel is actually achieved because of free fall — the astronaut and the space shuttle or rocket are both falling (or accelerating) at the same speeds. The same speed gives the notion of weightlessness or floating. This is the same concept as a person on a "free fall" ride at an amusement park. Both the rider and the ride are falling at the same speed causing the rider to seem as though he is falling independent of the ride. The same feeling can be experienced while riding an airplane or an elevator that suddenly breaks from its normal rate of decent.

What Is Buoyancy

Buoyancy is the ability of an object to float in a liquid. The relation of the object's weight to the weight of the water displaced is what determines if the object will float; although the size and shape of the object do have an effect, they are not the primary reason why an object floats or sinks. If an object displaces more water than its weight, it will float. Buoyancy is an important factor in the design of many objects and in a number of water-based activities, such as boating or scuba diving.

The Archimedes Principle

The mathematician Archimedes, who lived in the third century B.C., is credited with discovering much of how buoyancy works. According to legend, he was getting into a bath one day and noticed that the more he immersed himself in the water, the more its level rose. He realized that his body was displacing the water in the tub. Later, he determined that an object under water weighed less than an object in air. Through these and other realizations, he established what came to be known as the Archimedes Principle:

An object in fluid is buoyed up by a force equal to the weight of the fluid the object displaces.

Positive, Negative, and Neutral Buoyancy An object that floats in a liquid is positively buoyant. This means that the amount of water displaced by the object weighs more than the object itself. For example, a boat that weighs 50 lbs (23 kg) but displaces 100 lbs (45 kg) of water will easily float. The boat displaces more water than its weight in part because of its size and shape; most of the interior of a boat is air, which is very light. This explains why massive ocean liners float: as long as the water displaced weighs more than the ships themselves, they will not sink. Negative buoyancy is what causes objects to sink. It refers to an object whose weight is more than the weight of the liquid it displaces. For example, a pebble may weigh 25 grams, but if it only displaces 15 grams of water, it cannot float. If the 50 lbs (23 kg) boat was loaded down with 75 lbs (34 kg) of freight, it would no longer float because its weight (125 lbs or 56.69 kg) is heavier than the weight of the water it displaces (100 lbs or 45 kg). It is also possible for an object to be neutrally buoyant. This means that the object's weight and the amount of liquid it displaces are about the same. A neutrally buoyant object will hover in the liquid, neither sinking nor floating. A submarine can adjust it weight by adding or expelling water in special tanks called ballast tanks. By properly balancing its ballast, the sub can hover at various levels under the surface of the water without sinking. Size and Shape How much of an object's surface touches the water has an effect on its buoyancy. A very large ship has a lot of surface area, which means that the ship's weight is spread out over a lot of water, all of which is pushing up on the ship. If the same ship was in the water with the bow pointing down, it would start to sink because all of the weight is concentrated in one small area, and the water it is displacing weighs less than the weight of the ship. A common example used to demonstrate this is a person floating in water. If the person floats on her back, her entire body can stay at or near the water's surface. When she floats in the water with her feet down, she'll sink farther; typically, only her upper body will stay at the top of the water. Stability Stability in a fluid depends on the location of an object's center of buoyancy in relation to its center of gravity. An object's center of gravity is the point in the object where all of the object's weight appears to be concentrated; it can also be thought of as the average location of the object's weight. The center of buoyancy is the center of gravity of the water that the object has displaced. This is not in the water, but in the object floating on it. When the center of buoyancy is directly above the center of gravity, then the object will be stable. If, however, the center of gravity is above the center of buoyancy — as in a ship that is loaded with freight high above the water line — then the object becomes unstable. If the freight shifts to one side for any reason, the center of gravity and the center of buoyancy will no longer line up. The ship will tip over as the center of buoyancy tries to rise above the center of gravity again. In the human body, the center of gravity is usually in the area of the navel. The center of buoyancy is slightly higher, which is why a body tends to float upright with the shoulders and torso above the legs. Turned upside down, where the legs are above the torso, the body's center of gravity is above the center of buoyancy. This makes the body unstable, and the position can only be maintained through effort. Buoyancy in Practice By applying the principles of buoyancy, engineers can design boats, ships, and seaplanes that remain afloat and stable in water. This is true of many other objects, such as life preservers and pontoons. Just about anything designed for water relies on an understanding of these principles. Many swimmers know that there are ways to make their bodies more buoyant, such as lying on their backs or holding a full breath. In addition, trying to dive to the bottom of a pool takes effort because the body naturally floats. Scuba divers in particular need to know how to float, hover, and sink, and they often wear extra weights and other gear to help them manage these maneuvers.

What Is Urea

Urea, also called carbamide, is an organic chemical compound, and is essentially the waste produced by the body after metabolizing protein. Naturally, the compound is produced when the liver breaks down protein or amino acids, and ammonia; the kidneys then transfer the urea from the blood to the urine. Extra nitrogen is expelled from the body through urea, and because it is extremely soluble, it is a very efficient process. The average person excretes about 30 grams of urea a day, mostly through urine, but a small amount is also secreted in perspiration. Synthetic versions of the chemical compound can be created in liquid or solid form, and is often an ingredient found in fertilizers, animal feed, and diuretics, just to name a few.

Discovery

Naturally, the chemical compound is not only produced by humans but also by many other mammals, as well as amphibians and some fish. Discovered in 1773 by the French chemist Hillaire Rouelle, urea became the first organic compound to be synthetically formulated. German chemist Friedrich Wöhler, one of the pioneers of organic chemistry, invented the process to create the synthetic version of the compound in 1828, just 55 years after its discovery. 

Production

The synthetic version of the compound is created from ammonia and carbon dioxide and can be produced as a liquid or a solid. In 1870, the process of producing the compound synthetically by dehydrating ammonium carbamate under conditions of high heat and pressure was invented, and this process is still used today. There are many common uses of the synthetic compound, and therefore its production is high; in fact, approximately one million pounds of urea is manufactured in the United States alone each year.

Common Uses

Most of the manufactured compound is used in fertilizers; when nitrogen is added to urea, the compound becomes water soluble, making it a highly desired ingredient for lawn fertilizer. The synthetic version is also used commercially and industrially to produce some types of plastics, animal feed, glues, toilet bowl cleaners, dish washing machine detergents, hair coloring products, pesticides, and fungicides. Medicinally, it is used in barbiturates, dermatological products that re-hydrate the skin, and diuretics Physicians can use urea levels to detect diseases and disorders that affect the kidneys, such as acute kidney failure or end-stage renal disease (ESRD). The blood urea nitrogen (BUN) and the urine urea nitrogen (UUN) tests, which measure urea nitrogen levels in the blood and urine, are often used to assess how well a patient's kidneys are functioning. Increased or decreased levels of the compound, however, do not always indicate kidney problems, but instead may reflect dehydration or increased protein intake.

Why is Alcohol a Good Antiseptic

Ethyl alcohol, more frequently known as grain alcohol, works as an antiseptic by coagulating protein, the primary material that makes up cells. Although alcohol cannot coagulate every single cell, it functions well to inhibit the growth and reproduction of many microorganisms, including bacteria, fungi, protozoa, and viruses.

Intriguingly, 70% alcohol is a more effective antiseptic than 100% alcohol. Because alcohol causes protein to coagulate on contact, a 100% solution coming into contact with a microorganism creates a hardened protein wall around the outside of the organism, rather than permeating into its interior. Because microorganisms can be very resilient, this protein shell only causes dormancy rather than death. This can lead to revival and a continuation the cycle of reproduction under the right circumstances. At a purity of 70%, however, the alcohol causes coagulation to occur more gradually, slowing down the microorganism from the inside out.

Human skin cells are more resistant to alcoholic coagulation than most microorganisms. This is why your skin doesn't coagulate if it comes into contact with alcohol. Alcohol is also a good solvent that dissolves and carries away non-organic impurities that are responsible for things like odor. Its antiseptic action does cause a burning sensation on open flesh, as anyone who has ever used alcohol to clean a wound can testify.

Alcohol is an ideal antiseptic because it achieves its goal subtly through coagulation, rather than through some active means like active poisoning or dissolving. Throwing acid on an open wound would only be successful at removing the contaminating microorganisms at the expense of a decent chunk of flesh. Ethyl alcohol should never be confused with methyl alcohol, also known as methanol or wood alcohol. Methyl alcohol is used in industry as a solvent, and should never be used for any medical reason. Even small quantities can cause blindness or paralysis, and large quantities can be fatal.

What is G-Force

G-force refers to either the force of gravity on a particular celestial body or the force of acceleration anywhere. G-force is measured in g's, where 1 g equals the force of gravity at the Earth's surface (9.8 meters per second per second). As Einstein realized, the force of gravity and the forces of acceleration are mutually indistinguishable on the subject; a person in an opaque box experiencing a g-force would be unable to tell whether its origin lies in acceleration through space or a gravitational field unless they had some way of peeking outside the box. 

Analysis of g-forces are important in a variety of scientific and engineering fields, especially planetary science, astrophysics, rocket science, and the engineering of various machines such as fighter jets, race cars, and large engines. 

Humans can tolerate localized g-forces in the 100s of g's for a split second, such as a slap to the face. However, sustained g-forces above about 10 g can be deadly or lead to permanent injury. There is considerable variation among individuals when it comes to g-force tolerance, however. Race car drivers have survived instantaneous accelerations of up to 214 g during accidents. In rocket sled experiments designed to test the effects of high acceleration on the human body, Colonel John Stapp in 1954 experienced 46.2 g for several seconds. Usually, accelerations beyond 100 g, even if momentary, are fatal.

In everyday life, humans experience g-forces stronger than 1 g. A typical cough produces a momentary g-force of 3.5 g, while a sneeze results in about 3 g of acceleration. Roller coasters are usually designed not to exceed 3 g, although a few notable exceptions produce as much as 6.7 g. Slight increases in g-force are experienced in any moving machinery, such as cars, trains, planes, and elevators. Astronauts in orbit experience 0 g, called weightlessness.

G-force varies on different planets or celestial bodies. When an object has a greater mass, it produces a higher gravitational field, resulting in higher g-forces. The g-force on the Moon is about 1/6 g, on Mars about 1/3 g. On the Martian satellite Deimos, only 13 km (8 mi) in diameter, the g-force is about 4/10,000ths of a g. In contrast, the surface of Jupiter experiences a g-force of about 2.5 g. This is smaller than it seems it should be because Jupiter's low density causes its surface to be very far from its primary concentration of mass at the core. On the surface of a neutron star, a degenerate star with a density similar to the atomic nucleus, the surface gravity is between 2×10¹¹ and 3×10¹² gs.

What is a Non-Newtonian Fluid

A non-Newtonian fluid is a fluid whose viscosity is variable based on applied stress. The most commonly known non-Newtonian fluid is cornstarch dissolved in water. Contrast with Newtonian fluids like water, whose behavior can be described exclusively by temperature and pressure, not the forces acting on it from second to second. Non-Newtonian fluids are fascinating substances that can be used to help us understand physics in more detail, in an exciting, hands-on way.

If you punch a bucket full of a shear thickening non-Newtonian fluid, the stress introduced by the incoming force causes the atoms in the fluid to rearrange such that it behaves like a solid. Your hand will not go through. If you shove your hand into the fluid slowly, however, it will penetrate successfully. If you pull your hand out abruptly, it will again behave like a solid, and you can literally pull a bucket of the fluid out of its container in this way. 

A shear thinning non-Newtonian fluid behaves in the opposite way. In this type, the fluid becomes thinner, rather than thicker, when stress is applied. Also called pseudoplastic, examples of this type of non-Newtonian fluid include ketchup, toothpaste, and paint. The effect doesn't usually last for long in either type, continuing only as long as the stress is applied.

Non-Newtonian fluids help us understand the wide variety of fluids that exist in the physical world. Plastic solids, power-law fluids, viscoelastic fluids, and time-dependent viscosity fluids are others that exhibit complex and counterintuitive relationships between shear stress and viscosity/elasticity. However, non-Newtonian fluid is probably the most exciting to play with. 

A search for non-Newtonian fluid on YouTube brings up some interesting results. On several game shows, hosts or contestants run across big vats of shear thickening non-Newtonian fluid, able to traverse them unless they stop - in which case they sink immediately. When combined with a oscillating plate, non-Newtonian fluids demonstrate other unusual properties, like protruding "fingers" and holes that persist after creating them. An oscillating plate applies stress on a periodic basis, rapidly changing the viscosity of the fluid and putting it in an odd middle ground between a liquid and a solid.

A practical application for shear thickening non-Newtonian fluids may be in body armor of the future. Since such fluids are usually flexible, they would allow soldiers to move freely when not under attack. But if confronted with a speeding bullet, they would quickly harder, performing like traditional armor. More research is necessary to see if non-Newtonian fluids are suitable for the military, but until then, it's sure fun to play with.