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3 ATOMS Atoms are the smallest particles of matter that have the properties of the chemical elements - hydrogen, oxygen, iron, and so on. They are so small that it is impossible to see them even with a high-powered microscope. Everything on Earth is made up of atoms in different chemical combinations. Water, for instance, is a compound of two elements, two atoms of hydrogen and one atom of oxygen. However, some elements, such as gold and diamonds exist uncombined. Ninety-two elements occur naturally. They range from the lightest, hydrogen, to the heaviest, uranium. Each of the elements has been assigned a number - 1 for hydrogen, 8 for oxygen, 29 for copper, 92 for uranium. They are usually arranged on a chart called the periodic table, which puts elements with the same chemical properties in the same column. Thus, all inert gases, such as helium appear in one column in the periodic table. The formulation of the atomic theory is one of the great achievements of science. It has enabled us to understand the properties of the elements, the basic building blocks of all matter, so that we know which elements can combine with each other. The science of chemistry is based on our understanding of atoms and their behaviour in interacting with one another. Another science called nuclear physics came into being to study the structure of the atom itself. As scientists investigated the atom, it became apparent that the atom was not a solid piece of matter, but was made up of even smaller particles. The first subatomic particle that scientists identified was the electron a tiny piece of matter with a negative electric charge. The weight of an electron was very small indeed -approximately one eighteen-hundredth of the weight of a hydrogen atom, the lightest of all t elements. Scientists came to believe that the electrons orbited the nucleus of the atom, in which almost all of the weight of the atom was concentrated. It is now known that electrons revolve around the nucleus at incredibly fast rates of speed. For many years scientists did many different kinds of experiments and all had the same idea about the structure of atoms. However, when they managed to obtain more evidence, they had to modify the atomic theory. There was not just one kind of particle in the nucleus of an atom; there were two. One of these has a positive electric charge and is called a proton. The other is neutral. that is, it has no electric charge. For this reason, it was called a neutron.
4 MUSIC OR NOISE? Vibration is movement and sound that comes from objects which vibrate. For example, guitar strings, when touched, vibrate and make a sound; and drum skins, when hit, vibrate and make a sound. Vibrations are described in terms of amplitude and frequency. In the case of a guitar, the amplitude, or loudness, is the distance the string moves; and in the case of a drum, the skin moves at a certain speed and vibrates a certain number of times each second. If the skin, or the string, vibrates 440 times per second, then we say it has a frequency of 440 Hertz (or 440 Hz for short). If it moves faster or slower, then it has a higher or lower frequency. The human ear cannot detect all sounds. Sounds must have a certain amplitude, and a frequency between 40 Hz and 16,000 Hz. Vibrations above or below these will not be detected by the human ear even if they are extremely loud. Many animals have better hearing than us. Dogs, for example, can hear higher frequencies; and bats can hear sounds with incredibly high frequencies - up to 48,000 Hz. The vibrating object first causes the molecules in the air around II to vibrate at the same frequency and amplitude. These molecules then cause other molecules to vibrate and so it continues Until molecules of air inside our ears vibrate. Finally our eardrums vibrate and cause minute, i.e. very small, electrical signals to be sent to the brain. kaldım, kelime çıkarma All sounds come from vibrations. But not all sounds are the same. Some are pleasant to hear, such as music. Others are unpleasant and these we call noise. What's the difference between the two? This is a difficult question to answer. But the sounds of musical instruments, which are usually good to hear, do have a special characteristic: musical instruments, such as the guitar and the drum, vibrate at more than one frequency. Thus, when a guitar string produces the note of A, the vibration of greatest amplitude has a frequency of 440 Hz. But there are vibrations of other frequencies present, too. They have less amplitude, and so we do not consciously hear them. But they add to the sound and form a pattern of frequencies which is pleasant to hear. This is called harmonics. It is harmonics which help us to identify the musical instrument we hear. Of course, there are other characteristics of music, too. One of these is rhythm, the sequence of sounds. Rhythm is not exclusive to musical sound; but it is one of the factors which help make music pleasant to hear.
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