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The content of spray dusters is not normal air. They contain forms of gases that are easier to compress. These gases are in their liquid form while inside the high pressure confines of the can, and evaporate back into the gaseous state when they leave the can and return to normal pressure. This change is known as adiabatic expansion.
This expansion from liquid to gas requires a change in energy. The particles in a liquid are closer together and slower moving than the particles in gas form, and more energy is needed as the transition from liquid to gas takes place.
The energy needed for the transition to gas is felt as heat. To raise the temperature of the liquid enough to become gas, this heat is drawn from the surrounding air, a phenomenon called the Joule-Thomson effect. As the heat is drawn into the expanding gas, the surrounding air drops in temperature, which you experience as cooling. -
"The Universe" and "New Guide to Science" by Isaac Asimov
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By mass, human cells consist of 65-90% water (H2O), and a significant portion is composed of carbon-containing organic molecules. Oxygen therefore contributes a majority of a human body's mass, followed by carbon.
99% of the mass of the human body is made up of the six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus.
Oxygen 65 %
Carbon 18 %
Hydrogen 10 %
Nitrogen 3 %
Calcium 1.5 %
Phosphorus 1.2 %
Potassium 0.2 %
Sulfur 0.2 %
Chlorine 0.2 %
Sodium 0.1 %
Magnesium 0.05 %
Iron, Cobalt, Copper, Zinc, Iodine <0.05 % each
Selenium, Fluorine <0.01 % each -
An entity is something that has a distinct, separate existence, a basic matter part. So if we understand the entities of the universe as the basic and indivisible pieces that the Universe is made of, we have to be careful, since our knowledge has changed in the history of science a few times.
Scientists have believed they had reached the smallest parts that the Universe is made of in several occasions. That’s the origin of the word “atom”, which means indivisible. We thought we had reached the basic entity at least, but not for very long. Soon we realized that atoms were made of even smaller entities themselves. We discovered the elementary particles which atoms are made of. Once more we thought we had reached the bottom. And once more we were wrong. We discovered that some elementary particles were made of even smaller entities called quarks. There are some theories today that say that we are not even close to the final answer. The famous String theory is one of theses. We’re working on it. -
Auroras are associated with the solar wind, a flow of ions continuously flowing outward from the sun. The Earth's magnetic field traps these particles, many of which travel toward the poles where they are accelerated toward earth. Collisions between these ions and atmospheric atoms and molecules causes energy releases in the form of auroras appearing in large circles around the poles. Auroras are more frequent and brighter during the intense phase of the solar cycle when coronal mass ejections increase the intensity of the solar wind.
Auroras are the result of the emissions of photons in the Earth's upper atmosphere, above 80 km (50 miles), from ionized nitrogen atoms regaining an electron, and oxygen and nitrogen atoms returning from an excited state to ground state. They are ionized or excited by the collision of solar wind particles being funneled down and accelerated along the Earth's magnetic field lines; excitation energy is lost by the emission of a photon of light, or by collision with another atom or molecule:
Oxygen emissions: green or brownish-red, depending on the amount of energy absorbed.
Nitrogen emissions: blue or red. Blue if the atom regains an electron after it has been ionized. Red if returning to ground state from an excited state. -
Human evolution, or anthropogenesis, is the origin and evolution of Homo sapiens as a distinct species from other hominids, great apes and placental mammals.
Humans are one of the great apes (Family Hominidae) which are:
Genus Pongo (orangutans)
Genus Gorilla (gorillas)
Genus Homo (humans)
Genus Pan (chimpanzees)
The term "human" in the context of human evolution refers to the genus Homo, but studies of human evolution usually include other hominids. The genus Homo had diverged from the Australopithecines by about 2.3 to 2.4 million years ago in Africa. It’s estimated that humans branched off from their common ancestor with chimpanzees (the only other living hominins) about 5–7 million years ago. Several species of Homo evolved and are now extinct. These include Homo erectus, which inhabited Asia, and Homo neanderthalensis, which inhabited Europe. Archaic Homo sapiens evolved between 400,000 and 250,000 years ago.
The dominant view among scientists concerning the origin of anatomically modern humans is the "Out of Africa" or recent African origin hypothesis, which argues that H. sapiens arose in Africa and migrated out of the continent around 50-100,000 years ago, replacing populations of H. erectus in Asia and H. neanderthalensis in Europe. Scientists supporting the alternative multiregional hypothesis argue that H. sapiens evolved as geographically separate but interbreeding populations stemming from a worldwide migration of H. erectus out of Africa nearly 2.5 million years ago. -
This is basically how Evolution works:
Every time that life reproduces there are changes in the genetic code from one generation to the next. This small variations can take place for two main reasons:
1: recombination between the genes of the two parents
2: random mutations that occur in the process of transferring the new information to the next generation.
These changes from the previous generation to the next can make not very significant differences, they can be translated to worse qualities in the new generation from the previous one, or they can end up with better qualities from the parents. It's the environment who decides what changes are better and what changes are worse.
Those who improved their qualities to adapt to the environment (find best food, to escape from predators, etc.) will be better prepared to reproduce, and will have more chances to have descendants and pass their improved genes to the next generation than the rest of individuals. And it starts over again.
These slow changes from generations to generation end up changing the species. And during millions of years and millions of generations is creates new species from others very slowly. When you have different groups of live forms adapting to different environments separated geographically, you end up having complete different species. All of them coming from the first form of life, a common ancestor, through the ages on Earth. -
Even though it's not very clear yet the mechanisms of heritage in homosexuality, scientist has very clear there is a genetic component on it. The latest and more important studies on this matter, as well as the statistical research, shows clear evidence that there is a genetic fact.
The most successful scientific studies done on homosexuality that looked at families in which there was an abnormally high occurrence of homosexuality by looking at the family trees of gay males it seemed that the majority of homosexual occurrences were on the maternal side of the tree. From this information, researchers concluded that if in fact there was a "homosexual gene", it appeared to be passed down from mother to son. This means that heterosexual females are carriers of this gene and there is a chance that the child will be a homosexual. While this study did not come up with any hard core facts about the genetics of homosexuality, it showed that a connection very well could exist. Since this study did determine that the gene influencing homosexuality was carried by the mother, researchers participating in further studies knew that they could limit their search to the X chromosome. They discovered that homosexual brothers have a much higher likelihood of inheriting the same genetic sequence on the region of the X chromosome identified by Xq28, than heterosexual brothers of the same gay men. Keep in mind though, that this is just a region of the X chromosome, not a specific gene. Although researchers are hopeful, a single gene has not yet been identified.
Another significant fact is that the region of the X chromosome that very possibly could influence male homosexuality does not influence females in the same way. Female heterosexuals merely pass the gene sequence on to their sons.
This suggests that if genetics are responsible for homosexuality, we have a long way to go before we completely understand the gene loci that determine sexuality. -
A cylinder is a three-dimensional solid with 2 bases, 2 edges and 3 faces. You measure the volume of a cylinder in cubic units of measurement. To calculate the volume of a cylinder we need to know the radius of the circular cross-section of the cylinder and the height of the cylinder. Height is sometimes referred to as the length.
Then you go like this:
1: Multiply the height by Pi. (A)
2: Square the radius. (Multiply the radius by itself.) (B)
3: Multiply the product A by B.
Don't forget to write your answer in the proper cubic unit of measurement. -
The first law of thermodynamics, an expression of the principle of conservation of energy, states that energy can be transformed (changed from one form to another), but cannot be created or destroyed.
It's the application of the conservation of energy principle to heat and thermodynamic processes: “Change in internal energy equals the difference of heat transfer into the system and the work done by the system.”
It is typical for chemistry texts to write the first law as ΔU=Q-W
ΔU = increase in the internal energy
Q = heat added to the system
W = work done by the system
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