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III. Physical Sciences Review

CHEMISTRY

Chemistry refers to the composition, properties, and interactions of matter. Organic chemistry is about living things. Inorganic chemistry deals with all other substances. Matter consists of atoms, which are so small they have never been seen—not even with the most powerful microscope. Atoms contain three subatomic particles—protons, neutrons, and electrons. The nucleus contains positively charged protons and neutrons with a neutral charge. Negatively charged electrons revolve around the nucleus.

Elements are the building blocks of chemistry. They cannot be broken by chemical means into other elements. Over 100 chemical elements are known today. Some have been produced artificially and have not been found in nature. Atoms are the smallest piece of an element. Each element is classified by its atomic number, which is the total number of protons in the nucleus. Every element has its own symbol. Therefore, every substance can be represented by symbols that show how many atoms of each element it contains.

Matter is anything that has mass and takes up space. Matter can exist as a solid, liquid, or gas. The form of matter may change. For example, water becomes solid below freezing, and lead can be heated to a liquid. All matter is made up of atoms. The weight of matter is a measure of the force that gravity places on its mass. Matter is conserved. That is, it cannot be created or destroyed, but it can be converted into energy.

A compound is formed when two or more elements unite chemically. A molecule is the smallest part of a compound with the properties of that compound. There are three important types of chemical compounds-acids, bases, and salt. Acids dissolved in water produce hydrogen. Bases dissolved in water produce hydroxide. When acids and bases are combined chemically, they form salt.

A solution is formed when element(s) or compound(s) are dissolved in another substance. Club soda is a solution with carbon dioxide dissolved in water. Lemonade is a solution of lemon juice and sugar dissolved in water.

Chemical reactions occur when bonds between atoms form or break. Energy, usually as heat, is absorbed when bonds are formed and released when bonds are broken. Water cooled below freezing forms bonds-energy is absorbed and ice forms. Water heated above boiling releases bonds-energy is released and steam is formed.

PHYSICS

Physics began at the earliest time with an attempt to understand matter and forces. This study has progressed through relativity and atomic physics to today when physicists are concerned with elementary particles. Physics seeks to describe nature through a number of general state­ments or laws. These laws are often stated in mathematical form.

Mass is the amount of matter in a body and is a measure of the body’s inertia (resistance to change of motion). Weight is a measure of the force of gravity on a body. Weight and mass are different. Mass at rest is the same everywhere, but mass increases as it approaches the speed of light. Weight varies depending on its location in a gravitational field.

The density (specific gravity) of matter describes how compact the matter is. Archimedes discovered density and is reputed to have shouted “Eureka” in the process. He found that, in similar weights of lead and gold, the gold displaced less water, showing that it was more dense.

Physics is concerned with an object’s response to force and the resulting movement. Force is energy that causes a change in an object’s motion or shape. To explain force completely, you must describe both the magnitude and the direction. For example, two forces of the same mag­nitude pushing in the same direction are different from these same forces pushing at one another.

Velocity is described as magnitude (e. g., miles per hour) and direction (e. g., from 220 degrees). The magnitude portion of velocity is speed. The following formula describes the distance traveled for a constant velocity and a known time. For a time t and a constant velocity v the distance traveled d is: d = vt.

Newton’s three laws of motion are still most important in everyday life. We must remember, though, that recent theories have shown that these laws do not apply to objects traveling near the speed of light or for very small subatomic particles.

Newton’s First Law (Inertia). A body maintains its state of rest or uniform motion unless acted upon by an outside force.

Newton’s Second Law (Constant Acceleration). As force is applied to an object, the object accelerates in the direction of the force. Both the mass and the force affect how the object accelerates. The more the mass the less the acceleration. The formula for this law follows:

F(orce) = M(ass) x A(cceleration)

or

A(cceleration) = F(orce) / M(ass).

Newton’s Third Law (Conservation of Momentum). This law states that for every action there is an equal and opposite reaction. If two objects bump into each other, they are pushed away from each other with an equal force. The net effect of this event is 0, and the momentum is conserved.

Energy is the ability to do work. Energy can be mechanical, solar, thermal, chemical, electrical, or nuclear. Potential energy is stored energy or energy ready to be released. Kinetic energy is energy resulting from motion. Activation energy converts potential energy into kinetic energy.

Work is the movement of a body by a force. If there is no movement, there is no work. Work occurs when you pick up an object. Trying without success to move a heavy object or holding an object steady involves no work. It does not matter that a lot of effort was involved. The rate of work is power. Power is measured in foot-pounds. A foot-pound is the amount of work it takes to raise one pound, one foot at sea level.

In physics, heat is energy in motion. Heat transfers energy within a body or from one body to the other when there is a temperature difference. Heat moves from higher temperature to lower temperature, lowering the former and raising the latter. Heat is measured in calories. Temperature measures how fast the molecules in a substance are moving. The faster the molecules move, the hotter the substance. Temperature is commonly measured on two scales, Fahrenheit (freezing 32 degrees, boiling [water] 212 degrees) and Celsius (freezing 0 degrees and boiling [water] 100 degrees). The Kelvin scale is used in science. Zero on the Kelvin scale is absolute zero-molecules are not moving at all-and is equal to –273°C or –460°F. Heat is transferred by conduction (physical contact), convection (from moving liquid or gas), and radiation (no physical contact). A heating pad conducts heat to your back. Moving hot water transfers heat to the radiator by convection. The sun radiates heat to the earth.

Waves transfer energy without transferring matter. Microwaves, radio waves, sound waves, and x-rays are examples of waves in action. The frequency of a wave is the vibrations per second. The wavelength is the distance between crests.

Most light is produced by heated electrons vibrating at high frequencies. Light makes it possible for us to see things and to observe colors. Plants need light to carry out photosynthesis. Light travels in straight lines and spreads out as it travels. When light strikes a rough surface it may be absorbed or scattered. When light strikes a highly polished surface it is reflected away at the angle of the original ray (angle of incidence equals the angle of reflection). Black surfaces absorb all light, while white surfaces scatter all light. This is why white clothes are recommended for sunny, warm days.

Sounds are waves. For the human ear to hear a sound it must travel through a medium-a gas, a solid, or a liquid. As the sound waves travel through the medium, molecules in the medium vibrate. Sound travels more quickly through solid media because the molecules are more closely packed together. Sound travels through air at about 1,100 feet per second, through water at about 5,000 feet per second, and through stone at about 20,000 feet per second.

Atoms are composed of protons (positive charge), electrons (negative charge), and neutrons (neutral charge). All things have either a positive (more protons), negative (more electrons), or neutral (balance of protons and electrons) charge.

Electricity is based on these charges and follows these rules. Like charges repel, unlike charge attract. Neutral charges are attracted by both positive and negative charges, but not as strongly as opposite charges.

In a static electricity experiment, the experimenter shows that the glass rod does not attract bits of paper. Then the glass rod is rubbed with a piece of silk. This process removes electrons from the rod, creating a negative charge. Then the rod attracts the neutral bits of paper. Electricity speeds through conductors such as copper. Electricity moves slower through semiconductors such as ceramics. Electricity does not move through nonconductors or insulators such as rubber and glass.

Electricity moves through wires to form circuits. Most circuits in this country use alternating current (AC). Circuits in other countries may use direct current (DC). Most circuits are wired parallel-if a light burns out, or a switch is off, all other switches or lights work. Some circuits are wired in series-if a switch is off or a light is missing or burned out, all lights go out.

Three units are used to measure electricity as it flows through wires. The volt measures the force of the current. The ampere (amp) measures the rate of current flow. The ohm tells the resistance in the wire to the flow of electricity. Batteries are used to produce, store, and release electricity. Batteries used in a toy or flashlight are dry cell batteries. Car batteries are wet cell batteries.

Magnets occur naturally in magnetite, although most magnets are manufactured from iron. Magnetism is very similar to electricity, and electromagnets can be made from coils of wire. Magnets have a North and South Pole-like poles repel, while opposite poles attract. The magnetic field is strongest around the poles. Earth has a magnetic field that aids navigation. Magnetic north is located in northeastern Canada. It is not located at the North Pole. Compass needles point to magnetic north, not to the geographic North Pole.

Modern Physics studies very small particles of energy. Energy as very small, discrete quantities gives scientists a different view than energy as a continuous flow. Particle physics is particularly useful as scientists study atomic energy. For example, scientists study light as the transmission of tiny particles called photons. In fact, it is believed that energy is transmitted as both particles and waves. Modern physics also studies the conversion of matter into energy and energy into matter. Einstein’s famous equation quantifies the conversion between mass to energy. E = mc² (E is energy, т is mass, and с is the speed of light, 186,000 miles per second).

Calculations with this equation reveal that very small amounts of mass can create huge amounts of energy. Similarly, calculations reveal it would take huge amounts of energy to create a very small amount of mass.

Materials are radioactive when they have unstable nuclei. Uranium is an example of a naturally occurring radioactive substance. Radioactive materials decay, losing their radioactivity at a certain rate. The decay of radioactive materials is very useful for dating rocks and other materials. Other radioactive material is created through nuclear fission in nuclear power plants. The energy from the reaction can be used as a power source. Radioactive materials release energy including alpha, beta, and usually gamma radiation. Gamma rays penetrate living organisms very deeply and can destroy living cells and lead to the death of humans.

The sun creates energy through fusion. Attempts are underway to create energy through nuclear fusion. Fusion creates much less radioactivity and could be fueled by deuterium, which is found in limitless quantities throughout the ocean.

POST-READING ACTIVITIES