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.