1.
Surface tension
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Surface tension is the elastic tendency of a fluid surface which makes it acquire the least surface area possible. Surface tension allows insects, usually denser than water, to float, at liquid-air interfaces, surface tension results from the greater attraction of liquid molecules to each other than to the molecules in the air. The net effect is a force at its surface that causes the liquid to behave as if its surface were covered with a stretched elastic membrane. Thus, the surface becomes under tension from the imbalanced forces, because of the relatively high attraction of water molecules for each other through a web of hydrogen bonds, water has a higher surface tension compared to that of most other liquids. Surface tension is an important factor in the phenomenon of capillarity, Surface tension has the dimension of force per unit length, or of energy per unit area. The two are equivalent, but when referring to energy per unit of area, it is common to use the surface energy. In materials science, surface tension is used for either surface stress or surface free energy, the cohesive forces among liquid molecules are responsible for the phenomenon of surface tension. In the bulk of the liquid, each molecule is pulled equally in every direction by neighboring liquid molecules, the molecules at the surface do not have the same molecules on all sides of them and therefore are pulled inwards. This creates some internal pressure and forces liquid surfaces to contract to the minimal area, Surface tension is responsible for the shape of liquid droplets. Although easily deformed, droplets of water tend to be pulled into a shape by the imbalance in cohesive forces of the surface layer. In the absence of forces, including gravity, drops of virtually all liquids would be approximately spherical. The spherical shape minimizes the necessary wall tension of the surface according to Laplaces law. Another way to view surface tension is in terms of energy, a molecule in contact with a neighbor is in a lower state of energy than if it were alone. The interior molecules have as many neighbors as they can possibly have, for the liquid to minimize its energy state, the number of higher energy boundary molecules must be minimized. The minimized quantity of boundary molecules results in a surface area. As a result of surface area minimization, a surface will assume the smoothest shape it can, since any curvature in the surface shape results in greater area, a higher energy will also result. Consequently, the surface will push back against any curvature in much the way as a ball pushed uphill will push back to minimize its gravitational potential energy. Bubbles in pure water are unstable, the addition of surfactants, however, can have a stabilizing effect on the bubbles
2.
Pendant
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The word pendant derives from the Latin word pendere, and Old French word pendre, both of which translate to to hang down. It comes in the form of a piece of jewellery, generally attached by a small loop to a necklace. A pendant earring is an earring with a piece hanging down, in some case though the separation between necklace and pendant is far clearer. Pendants are among the oldest recorded types of bodily adornment, stone, shell, pottery, and more perishable materials were used. Ancient Egyptians commonly wore pendants, some shaped like hieroglyphs, pendants can have several functions, which may be combined, Award Identification Ornamentation Ostentation. Protection Self-affirmation The many specialized types of pendants include lockets which open, often to reveal an image, and pendilia, throughout the ages, pendants have come in a variety of forms to serve a variety of purposes. Though amulets come in forms, a wearable amulet worn around the neck or on the arm or leg in the form of a pendant is the most common. These are objects believed to possess magical or spiritual power to protect the wearer from danger or dispel evil influences, similar to an amulet, a talisman is an object believed to possess supernatural traits. However, while an amulet is strictly a defensive object, a talisman is meant to confer special benefits or powers upon the wearer. A locket is an object that opens to reveal a space which serves to hold a small object. They typically come in the form of a pendant hanging from a necklace, a medallion is most often a coin-shaped piece of metal worn as a pendant around the neck or pinned onto clothing. These are generally granted as awards, recognitions, or religious blessings, tools worn as pendants include Maori pounamu pendants. Shepherds whistles, bosuns whistles, and ocarinas can also be made as pendants, portable astronomical and navigational instruments were made as pendants. In the first decade of the 21st century, jewellers started to incorporate USB flash drives into pendants
3.
Viscosity
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The viscosity of a fluid is a measure of its resistance to gradual deformation by shear stress or tensile stress. For liquids, it corresponds to the concept of thickness, for example. Viscosity is a property of the fluid which opposes the motion between the two surfaces of the fluid in a fluid that are moving at different velocities. For a given velocity pattern, the stress required is proportional to the fluids viscosity, a fluid that has no resistance to shear stress is known as an ideal or inviscid fluid. Zero viscosity is observed only at low temperatures in superfluids. Otherwise, all fluids have positive viscosity, and are said to be viscous or viscid. A fluid with a high viscosity, such as pitch. The word viscosity is derived from the Latin viscum, meaning mistletoe, the dynamic viscosity of a fluid expresses its resistance to shearing flows, where adjacent layers move parallel to each other with different speeds. It can be defined through the situation known as a Couette flow. This fluid has to be homogeneous in the layer and at different shear stresses, if the speed of the top plate is small enough, the fluid particles will move parallel to it, and their speed will vary linearly from zero at the bottom to u at the top. Each layer of fluid will move faster than the one just below it, in particular, the fluid will apply on the top plate a force in the direction opposite to its motion, and an equal but opposite one to the bottom plate. An external force is required in order to keep the top plate moving at constant speed. The magnitude F of this force is found to be proportional to the u and the area A of each plate. The proportionality factor μ in this formula is the viscosity of the fluid, the ratio u/y is called the rate of shear deformation or shear velocity, and is the derivative of the fluid speed in the direction perpendicular to the plates. Isaac Newton expressed the forces by the differential equation τ = μ ∂ u ∂ y, where τ = F/A. This formula assumes that the flow is moving along parallel lines and this equation can be used where the velocity does not vary linearly with y, such as in fluid flowing through a pipe. Use of the Greek letter mu for the dynamic viscosity is common among mechanical and chemical engineers. However, the Greek letter eta is used by chemists, physicists
4.
Adhesion
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Adhesion is the tendency of dissimilar particles or surfaces to cling to one another. The forces that cause adhesion and cohesion can be divided into several types, the intermolecular forces responsible for the function of various kinds of stickers and sticky tape fall into the categories of chemical adhesion, dispersive adhesion, and diffusive adhesion. In addition to the magnitudes of these intermolecular forces, there are certain emergent mechanical effects. Surface energy is defined as the work that is required to build an area of a particular surface. Another way to view the energy is to relate it to the work required to cleave a bulk sample. If the new surfaces are identical, the surface energy γ of each surface is equal to half the work of cleavage, W, γ = W11. If the surfaces are unequal, the Young-Dupré equation applies, W12 = γ1 + γ2 – γ12 and this methodology can also be used to discuss cleavage that happens in another medium, γ12 = W121 = W212. These two energy quantities refer to the energy that is needed to one species into two pieces while it is contained in a medium of the other species. Likewise for a three species system, γ13 + γ23 – γ12 = W12 + W33 – W13 – W23 = W132, there is no single theory covering adhesion, and particular mechanisms are specific to particular material scenarios. Five mechanisms of adhesion have been proposed to explain why one material sticks to another, Adhesive materials fill the voids or pores of the surfaces, other interlocking phenomena are observed on different length scales. Sewing is an example of two forming a large scale mechanical bond, velcro forms one on a medium scale. Two materials may form a compound at the joint, the strongest joints are where atoms of the two materials swap or share electrons. A weaker bond is formed if an atom in one molecule is attracted to an atom of nitrogen, oxygen, or fluorine in another molecule. Chemical adhesion occurs when the atoms of two separate surfaces form ionic, covalent, or hydrogen bonds. The engineering principle behind chemical adhesion in this sense is fairly straightforward, if surface molecules can bond and it bears mentioning that these attractive ionic and covalent forces are effective over only very small distances – less than a nanometer. In surface science, the term adhesion almost always refers to dispersive adhesion, in a typical solid-liquid-gas system the contact angle is used to evaluate adhesiveness indirectly, while a Centrifugal Adhesion Balance allows for direct quantitative adhesion measurements. Generally, cases where the angle is low are considered of higher adhesion per unit area. This approach assumes that the contact angle corresponds to a higher surface energy
5.
Gravity
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Gravity, or gravitation, is a natural phenomenon by which all things with mass are brought toward one another, including planets, stars and galaxies. Since energy and mass are equivalent, all forms of energy, including light, on Earth, gravity gives weight to physical objects and causes the ocean tides. Gravity has a range, although its effects become increasingly weaker on farther objects. The most extreme example of this curvature of spacetime is a hole, from which nothing can escape once past its event horizon. More gravity results in time dilation, where time lapses more slowly at a lower gravitational potential. Gravity is the weakest of the four fundamental interactions of nature, the gravitational attraction is approximately 1038 times weaker than the strong force,1036 times weaker than the electromagnetic force and 1029 times weaker than the weak force. As a consequence, gravity has an influence on the behavior of subatomic particles. On the other hand, gravity is the dominant interaction at the macroscopic scale, for this reason, in part, pursuit of a theory of everything, the merging of the general theory of relativity and quantum mechanics into quantum gravity, has become an area of research. While the modern European thinkers are credited with development of gravitational theory, some of the earliest descriptions came from early mathematician-astronomers, such as Aryabhata, who had identified the force of gravity to explain why objects do not fall out when the Earth rotates. Later, the works of Brahmagupta referred to the presence of force, described it as an attractive force. Modern work on gravitational theory began with the work of Galileo Galilei in the late 16th and this was a major departure from Aristotles belief that heavier objects have a higher gravitational acceleration. Galileo postulated air resistance as the reason that objects with less mass may fall slower in an atmosphere, galileos work set the stage for the formulation of Newtons theory of gravity. In 1687, English mathematician Sir Isaac Newton published Principia, which hypothesizes the inverse-square law of universal gravitation. Newtons theory enjoyed its greatest success when it was used to predict the existence of Neptune based on motions of Uranus that could not be accounted for by the actions of the other planets. Calculations by both John Couch Adams and Urbain Le Verrier predicted the position of the planet. A discrepancy in Mercurys orbit pointed out flaws in Newtons theory, the issue was resolved in 1915 by Albert Einsteins new theory of general relativity, which accounted for the small discrepancy in Mercurys orbit. The simplest way to test the equivalence principle is to drop two objects of different masses or compositions in a vacuum and see whether they hit the ground at the same time. Such experiments demonstrate that all objects fall at the rate when other forces are negligible
6.
Pesticide application
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Pesticide application refers to the practical way in which pesticides, are delivered to their biological targets. Public concern about the use of pesticides has highlighted the need to make this process as efficient as possible, in order to minimise their release into the environment, seed treatments can achieve exceptionally high efficiencies, in terms of effective dose-transfer to a crop. One of the most common forms of application, especially in conventional agriculture, is the use of mechanical sprayers. Hydraulic sprayers consists of a tank, a pump, a lance or boom, sprayers convert a pesticide formulation, often containing a mixture of water and chemical, into droplets, which can be large rain-type drops or tiny almost-invisible particles. This conversion is accomplished by forcing the mixture through a spray nozzle under pressure. The size of droplets can be altered through the use of different nozzle sizes, or by altering the pressure under which it is forced, large droplets have the advantage of being less susceptible to spray drift, but require more water per unit of land covered. Due to static electricity, small droplets are able to contact with a target organism. Traditional agricultural crop pesticides can either be applied pre-emergent or post-emergent, an example of pre-emergent pesticide application is atrazine application for corn. Similarly, glyphosate mixtures are often applied pre-emergent on agricultural fields to remove early-germinating weeds, pre-emergent application equipment often has large, wide tires designed to float on soft soil, minimizing both soil compaction and damage to planted crops. Post-emergent pesticide application requires the use of specific chemicals chosen minimize harm to the target organism. An example is 2, 4-Dichlorophenoxyacetic acid, which will injure broadleaf weeds, such a chemical has been used extensively on wheat crops, for example. A number of companies have also created genetically modified organisms that are resistant to various pesticides, examples include glyphosate-resistant soybeans and Bt maize, which change the types of formulations involved in addressing post-emergent pesticide pressure. As plants have already germinated, post-emergent pesticide application necessitates limited field contact in order to minimize losses due to crop, typical industrial application equipment will utilize very tall and narrow tires and combine this with a sprayer body which can be raised and lowered depending on crop height. These sprayers usually carry the label ‘high-clearance’ as they can rise over growing crops, in addition, these sprayers often have very wide booms in order to minimize the number of passes required over a field, again designed to limit crop damage and maximize efficiency. In industrial agriculture, spray booms 120 feet wide are not uncommon, especially in agriculture with large. Related to this, aerial pesticide application is a method of top dressing a pesticide to a crop which eliminates physical contact with soil. Air Blast sprayers, also known as air-assisted or mist sprayers, are used for tall crops, such as tree fruit. These can be used for insects, weeds, and other pests to crops, humans, air blast sprayers inject liquid into a fast-moving stream of air, breaking down large droplets into smaller particles by introducing a small amount of liquid into a fast-moving stream of air
7.
Water
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Water is a transparent and nearly colorless chemical substance that is the main constituent of Earths streams, lakes, and oceans, and the fluids of most living organisms. Its chemical formula is H2O, meaning that its molecule contains one oxygen, Water strictly refers to the liquid state of that substance, that prevails at standard ambient temperature and pressure, but it often refers also to its solid state or its gaseous state. It also occurs in nature as snow, glaciers, ice packs and icebergs, clouds, fog, dew, aquifers, Water covers 71% of the Earths surface. It is vital for all forms of life. Only 2. 5% of this water is freshwater, and 98. 8% of that water is in ice and groundwater. Less than 0. 3% of all freshwater is in rivers, lakes, and the atmosphere, a greater quantity of water is found in the earths interior. Water on Earth moves continually through the cycle of evaporation and transpiration, condensation, precipitation. Evaporation and transpiration contribute to the precipitation over land, large amounts of water are also chemically combined or adsorbed in hydrated minerals. Safe drinking water is essential to humans and other even though it provides no calories or organic nutrients. There is a correlation between access to safe water and gross domestic product per capita. However, some observers have estimated that by 2025 more than half of the population will be facing water-based vulnerability. A report, issued in November 2009, suggests that by 2030, in developing regions of the world. Water plays an important role in the world economy, approximately 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies is a source of food for many parts of the world. Much of long-distance trade of commodities and manufactured products is transported by boats through seas, rivers, lakes, large quantities of water, ice, and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a variety of chemical substances, as such it is widely used in industrial processes. Water is also central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, surfing, sport fishing, Water is a liquid at the temperatures and pressures that are most adequate for life. Specifically, at atmospheric pressure of 1 bar, water is a liquid between the temperatures of 273.15 K and 373.15 K
8.
Refraction
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Refraction is the change in direction of wave propagation due to a change in its transmission medium. The phenomenon is explained by the conservation of energy and the conservation of momentum, due to the change of medium, the phase velocity of the wave is changed but its frequency remains constant. This is most commonly observed when a wave passes from one medium to another at any other than 0° from the normal. In optics, refraction is a phenomenon that occurs when waves travel from a medium with a given refractive index to a medium with another at an oblique angle. At the boundary between the media, the phase velocity is altered, usually causing a change in direction. Its wavelength increases or decreases, but its frequency remains constant, for example, a light ray will refract as it enters and leaves glass, assuming there is a change in refractive index. A ray traveling along the normal will change speed, but not direction, refraction still occurs in this case. Understanding of this led to the invention of lenses and the refracting telescope. Refraction can be seen looking into a bowl of water. Air has a index of about 1.0003. If a person looks at an object, such as a pencil or straw, which is placed at a slant, partially in the water. This is due to the bending of light rays as they move from the water to the air, once the rays reach the eye, the eye traces them back as straight lines. The lines of sight intersect at a position than where the actual rays originated. This causes the pencil to appear higher and the water to appear shallower than it really is, the depth that the water appears to be when viewed from above is known as the apparent depth. This is an important consideration for spearfishing from the surface because it will make the fish appear to be in a different place. Conversely, an object above the water has a higher apparent height when viewed from below the water, the opposite correction must be made by an archer fish. For small angles of incidence, the ratio of apparent to real depth is the ratio of the indexes of air to that of water. But, as the angle of incidence approaches 90o, the apparent depth approaches zero, albeit reflection increases, the diagram on the right shows an example of refraction in water waves
9.
Rain
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Rain is liquid water in the form of droplets that have condensed from atmospheric water vapor and then precipitated—that is, become heavy enough to fall under gravity. Rain is a component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides suitable conditions for many types of ecosystems, as well as water for power plants. The major cause of production is moisture moving along three-dimensional zones of temperature and moisture contrasts known as weather fronts. If enough moisture and upward motion is present, precipitation falls from convective clouds such as cumulonimbus which can organize into narrow rainbands. On the leeward side of mountains, desert climates can exist due to the dry air caused by downslope flow which causes heating and drying of the air mass, the movement of the monsoon trough, or intertropical convergence zone, brings rainy seasons to savannah climes. The urban heat island effect leads to increased rainfall, both in amounts and intensity, downwind of cities, global warming is also causing changes in the precipitation pattern globally, including wetter conditions across eastern North America and drier conditions in the tropics. The globally averaged annual precipitation over land is 715 mm, climate classification systems such as the Köppen climate classification system use average annual rainfall to help differentiate between differing climate regimes. Rainfall is measured using rain gauges, rainfall amounts can be estimated by weather radar. Rain is also known or suspected on other planets, where it may be composed of methane, neon, sulfuric acid, or even iron rather than water. Air contains water vapor, and the amount of water in a mass of dry air. The amount of moisture in air is commonly reported as relative humidity. How much water vapor a parcel of air can contain before it becomes saturated, warmer air can contain more water vapor than cooler air before becoming saturated. Therefore, one way to saturate a parcel of air is to cool it, the dew point is the temperature to which a parcel must be cooled in order to become saturated. There are four mechanisms for cooling the air to its dew point, adiabatic cooling, conductive cooling, radiational cooling. Adiabatic cooling occurs when air rises and expands, the air can rise due to convection, large-scale atmospheric motions, or a physical barrier such as a mountain. Conductive cooling occurs when the air comes into contact with a surface, usually by being blown from one surface to another. Radiational cooling occurs due to the emission of infrared radiation, either by the air or by the surface underneath, evaporative cooling occurs when moisture is added to the air through evaporation, which forces the air temperature to cool to its wet-bulb temperature, or until it reaches saturation
10.
Rainbow
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A rainbow is a meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky. It takes the form of a multicoloured arc, Rainbows caused by sunlight always appear in the section of sky directly opposite the sun. However, the observer sees only an arc formed by illuminated droplets above the ground. In a primary rainbow, the arc shows red on the outer part and this rainbow is caused by light being refracted when entering a droplet of water, then reflected inside on the back of the droplet and refracted again when leaving it. In a double rainbow, an arc is seen outside the primary arc. A rainbow is not located at a distance from the observer. Thus, a rainbow is not an object and cannot be physically approached, indeed, it is impossible for an observer to see a rainbow from water droplets at any angle other than the customary one of 42 degrees from the direction opposite the light source. Even if an observer sees another observer who seems under or at the end of a rainbow, Rainbows span a continuous spectrum of colours. Rainbows can be caused by many forms of airborne water and these include not only rain, but also mist, spray, and airborne dew. Rainbows can be observed there are water drops in the air. Because of this, rainbows are seen in the western sky during the morning. The most spectacular rainbow displays happen when half the sky is dark with raining clouds. The result is a rainbow that contrasts with the darkened background. During such good visibility conditions, the larger but fainter secondary rainbow is often visible and it appears about 10° outside of the primary rainbow, with inverse order of colours. The rainbow effect is commonly seen near waterfalls or fountains. In addition, the effect can be created by dispersing water droplets into the air during a sunny day. Rarely, a moonbow, lunar rainbow or nighttime rainbow, can be seen on strongly moonlit nights, as human visual perception for colour is poor in low light, moonbows are often perceived to be white. It is difficult to photograph the complete semicircle of a rainbow in one frame, for a 35 mm camera, a wide-angle lens with a focal length of 19 mm or less would be required
