Category Science

The air around us is a mixture of gases. Its content varies depending on where and when it is measured, but on average the air is made up of just over one-fifth oxygen and just under four-fifths nitrogen. There are also very small quantities of other gases, such as argon and carbon dioxide, some pollutants and water vapour, and tiny solid particles, such as soot and pollen.

The Earth’s atmosphere is a layer of gas held in place by gravity, which prevents it from escaping into space. It protects life by absorbing UV radiation, by holding in heat to warm the Earth’s surface and by reducing temperature extremes between day and night. The gases that comprise the atmosphere are commonly referred to as air, which is what all living things on Earth breathe.

It’s a common misconception that oxygen is the most abundant gas in the air breathed on Earth; that honor goes to nitrogen, which makes up 78 percent of the air. Nitrogen occurs as N2 — two nitrogen atoms bonded together. The bond is very strong, making the gas chemically inert. Although inhaled nitrogen passes into the bloodstream, it is not used by the cells in the body. However, since nitrogen is essential for life — it is found in RNA, DNA and proteins — it must be converted to compounds with less stable bonds to be used by animals. One way this happens is through nitrogen fixation in plants.

Making up almost 21 percent of the air all living things breathe, oxygen is absorbed by the lungs, or lung-like structures in lower animals, and transported to all cells in the body by the blood. Oxygen is the most unstable, and therefore the most chemically active, gas found in air. Although all animals need oxygen, it can be deadly in higher-than-normal concentrations: Breathing pure oxygen for extended periods leads to oxygen toxicity. In addition to its role in biology, oxygen is essential for combustion, the chemical process responsible for fire.

The third-most abundant gas in the air on Earth is argon, although it makes up less than 1 percent of air. Argon is classified as a noble gas in chemistry, meaning it is very stable and seldom reacts with other compounds. The argon in the air comes mainly from the decay of potassium-40, a radioactive isotope in the Earth’s crust. The bulk of argon used in science is acquired by fractional distillation of air in its liquid form.

There are several additional gases present in the atmosphere in minute amounts. These gases are referred to as trace gases and include water vapor, carbon dioxide, methane, helium, hydrogen and ozone. These gases each have their own purpose and forms of production. Methane, for example, is a powerful greenhouse gas, trapping heat in the earth’s atmosphere. Ozone is found in two distinct layers of the atmosphere: high in the stratosphere, where it blocks harmful ultraviolet light from the sun, and the lower atmosphere, where it is one of the components of smog.

As objects are dropped and pulled towards Earth by its gravitational force, they accelerate; travelling faster and faster the further they fall. That is why a person falling one metre might sustain only bruises but a person falling one kilometre would be unlikely to survive. The body would be hitting the ground at a much higher speed. However, an Italian scientist called Galileo Galilei, working some years before Newton, showed that the weight of a body does not affect the speed with which it falls.

Have you ever wondered how fast a heavy object falls compared with a lighter one? Imagine if you dropped both of them at the same time. Which would hit the ground first? Would it be the heavier one because it weighs more? Or would they hit the ground at the same time? In the late 1500s in Italy the famous scientist Galileo was asking some of these same questions. And he did some experiments to answer them. In this activity you’ll do some of your own tests to determine whether heavier objects fall faster than lighter ones.

In fourth-century B.C. Greece the philosopher Aristotle theorized that the speed at which an object falls is probably relative to its mass. In other words, if two objects are the same size but one is heavier, the heavier one has greater density than the lighter object. Therefore, when both objects are dropped from the same height and at the same time, the heavier object should hit the ground before the lighter one.

Some 1,800 years later, in late 16th-century Italy, the young scientist and mathematician Galileo Galilei questioned Aristotle’s theories of falling objects. He even performed several experiments to test Aristotle’s theories. As legend has it, in 1589 Galileo stood on a balcony near the top of the Tower of Pisa and dropped two balls that were the same size but had different densities. Although there is debate about whether this actually happened, the story emphasizes the importance of using experimentation to test scientific theories, even ones that had been accepted for nearly 2,000 years.

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Any sport that requires a participant or piece of equipment to be stable uses the principle of the centre of gravity.

Every single body and thus the athletes themselves, is made up of individual components each of which has its own weight. So our weight is just the sum of individual weights, of components such as our arms, legs, etc. The point, about which the distribution of these individual weights is symmetrical, is the center of gravity of the body. Thus, if a body has more mass distributed in its upper part, the center of gravity will be closer to the top of the body. This applies to humans, as the center of gravity of an average person is located approximately at a height of one meter, thus being above the waist.

There are two properties of the center of gravity that have a great impact on sport. First of all its location is dependent on the shape of the body. So if the same body is to take a different shape, the position of the center of gravity will shift. An athlete that bends his/her legs will lower his/her center of gravity position. This, amongst other things, will result in greater stability, something especially important in sports such as wrestling. Also, and this may sound the strangest, the center of gravity can lie entirely outside the body itself. For example, if the body is hollow it will literally be positioned somewhere in the air. During the Olympic Games in Mexico, in 1968, an, until then unknown athlete, the American Dick Fosbury, came from nowhere to teach the world about both of these properties.

The truly ingenious leap (!) in the technique was that by clearing the bar with his back and by changing the shape of his body, the athlete could clear the bar without his center of gravity having to also clear it. By this change in body shape he was able to move his center of gravity outside his body. The energy required for a jump depends on the maximum height of the center of gravity and so by lowering its position one also lowers the energy required to clear the bar.

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The force of gravity depends on the mass of the object exerting the gravitational pull. Generally, large planets have a greater gravitational force than smaller ones. As the Moon’s mass is smaller than that of the Earth, it exerts a gravitational pull only a sixth as strong as the gravity on Earth. That is why astronauts appear to bounce along on the Moon’s surface — the Moon is pulling them down much less strongly than on Earth. But the principle of gravity holds true throughout the universe.

A multi-decade analysis of a distant pulsar is affirming the longstanding notion that the gravitational constant—one of four fundamental forces of nature—is the same everywhere in the universe.

“Gravity is the force that binds stars, planets, and galaxies together,” noted study co-author Scott Ransom from the National Radio Astronomy Observatory in Charlottesville, Va. in a statement. “Though it appears on Earth to be constant and universal, there are some theories in cosmology that suggest gravity may change over time or may be different in different corners of the Universe.”

The new study, which now appears in the latest issue of the Astrophysical Journal, suggests these alternative theories are nothing more than a wild goose chase. As Albert Einstein surmised a century ago, the gravitational constant is a universal constant—an immutable law of the cosmos that permeates every region of space, regardless of time or distance.

The researchers analyzed 21 years’ worth of pulsar timing data collected by the NSF’s Robert C. Byrd Green Bank Telescope. Pulsars are the “lighthouses” of the universe—rapidly rotating neutron stars that generate super-concentrated beams of electromagnetic radiation that can only be detected by an observer situated directly in their path. Because of their diminutive size—they only measure about 20 to 25 kilometers (12 to 15 miles) across—they spin with a rate of precision that rivals the best atomic clocks on Earth. This consistency allows astronomers and cosmologists to study fundamental aspects of space, time, and gravity.

For the study, the researchers analyzed a pulsar binary, dubbed J1713+0747, located some 3,750 light-years away. This pulsar is special, not only because of its brightness, but because of its companion, a white dwarf, that’s located reasonably far enough away for the researchers to measure gravitational effects between the pair, and gravitational radiation in particular. Gravitational radiation, predicted by Einstein, is the steady conversion of orbital velocity to gravitational waves.

The researchers demonstrated that the gravitational constant we observe here on Earth is the same in a distant star system.

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The centre of gravity or centre of mass of an object is the point from which all its weight seems to act. The lower an object’s centre of gravity, the more stable it is. That is why decanters for holding water or wine often have wide, heavy bases, giving them a low centre of gravity, to make them difficult to knock over. When an object is tilted, it is still stable while its centre of gravity is over its base. If the object is tilted further, so that its centre of gravity is no longer over its base, it becomes unstable and will fall over.

Centre of gravity, in physics, an imaginary point in a body of matter where, for convenience in certain calculations, the total weight of the body may be thought to be concentrated. The concept is sometimes useful in designing static structures (e.g., buildings and bridges) or in predicting the behaviour of a moving body when it is acted on by gravity.

In a uniform gravitational field the centre of gravity is identical to the centre of mass, a term preferred by physicists. The two do not always coincide, however. For example, the Moon’s centre of mass is very close to its geometric centre (it is not exact because the Moon is not a perfect uniform sphere), but its centre of gravity is slightly displaced toward Earth because of the stronger gravitational force on the Moon’s near side.

The location of a body’s centre of gravity may coincide with the geometric centre of the body, especially in a symmetrically shaped object composed of homogeneous material. An asymmetrical object composed of a variety of materials with different masses, however, is likely to have a centre of gravity located at some distance from its geometric centre. In some cases, such as hollow bodies or irregularly shaped objects, the centre of gravity (or centre of mass) may occur in space at a point external to the physical material—e.g., in the centre of a tennis ball or between the legs of a chair.

Published tables and handbooks list the centres of gravity for most common geometric shapes. For a triangular metal plate such as that depicted in the figure, the calculation would involve a summation of the moments of the weights of all the particles that make up the metal plate about point A. By equating this sum to the plate’s weight W, multiplied by the unknown distance from the centre of gravity G to AC, the position of G relative to AC can be determined. The summation of the moments can be obtained easily and precisely by means of integral calculus.

The centre of gravity of anybody can also be determined by a simple physical procedure. For example, for the plate in the figure, the point G can be located by suspending the plate by a cord attached at point A and then by a cord attached at C. When the plate is suspended from A, the line AD is vertical; when it is suspended from C, the line CE is vertical. The centre of gravity is at the intersection of AD and CE. When an object is suspended from any single point, its centre of gravity lies directly beneath that point.