Ebook Encyclopedia physics (Volume 6)

Rourke’s World of Science Volume 6 Physics By Nancy Harris Editorial Consultant Luana Mitten Project Editor Kurt Sturm Table of Contents What is Physics? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Mass, Length, and Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Motion and Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 The Four Fundamental Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 Velocity and Acceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 Newton’s Three Laws of Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 Friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12 Circular Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13 Gravity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17 Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17 Simple Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17 Forms of Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23 Conservation of Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23 Potential and Kinetic Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24 Momentum and Collisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26 Electricity and Magnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27 Electric Charges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27 Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30 Magnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32 Heat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36 Expansion and Contraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37 How Heat Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40 The Uses of Heat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41 Waves, Sound, and Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43 Waves and Sound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43 The Nature of Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45 Where Light Comes From . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48 Reflection and Refraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48 Nuclear Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52 Uses of Nuclear Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53 Fission and Fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54 People Who Study Physics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60 4 Physics What Is Physics? Physics is the science of how the universe works. It is a science based on experiments, observation, and measurement. Experiments involve making things change. Observation is when scientists watch what they are studying very carefully. Measurement is describing things by their weight, size, or temperature. Physics looks at how tiny atoms are put together. Atoms are tiny particles that make up everything in the universe. Physics looks at how huge planets and stars move. It helps scientists understand the way matter acts. Matter includes the solids, liquids, and gases in the universe. Physics also helps scientists understand how energy acts. A physicist uses precise measurements. The protons and neutrons in the nucleus of an atom are surrounded by a cloud of electrons. Astrophysicists are physicists who study the stars and planets. Physics Energy Energy is everywhere. Energy is the ability to do work. It takes on many different forms. Energy is stored inside atoms. Light and 5 other’s results. The three fundamental units of measurement they use are mass, length, and time. Mass, Length, and Time sound are forms of energy. One way or another, everything is energy. People who study physics study how energy is used. They study how energy changes. Scientists are constantly improving the understanding of the basic, or fundamental, laws of nature. New discoveries are being made every day. These discoveries have a big effect on how people live and what they do. Mass measures the amount of material in an object Length measures how long something is Time measures how long changes take Plants get their energy from the Sun. Animals get their energy from plants or from eating other animals. Mass, Length, and Time The laws of physics can be described in simple terms. These terms explain the way the universe works. Scientists use units of measurement to describe what they do. This is done so that all scientists can understand each atom (AT-uhm): very small part of an element energy (EN-ur-jee): the ability to do work experiment (ek-SPER-uh-ment): trying to make substances change and recording what happens matter (MAT-ur): anything that takes up space and has mass (size) measurement (MEZH-ur-ment): saying how big something is, how much it weighs, or how hot it is observation (ob-zur-VAY-shuhn): when scientists watch what they are studying very carefully and write down what they see physics (FIZ-iks): the study of matter and energy 6 Physics In physics, the International System of Units is used to measure things. This system is based on the metric system. The metric system Motion and Force Motion uses specific units of measurement. The International System Unit of mass is the kilogram. The basic unit of length is the meter. The basic unit of time is the second. Scientists can describe almost everything by using these units in different combinations. International System of Units Kilogram (kg) used to measure mass Everything is in motion. Both small things and big things move. People and animals move about on the surface of the Earth. The Earth itself rotates (turns) and moves in an orbit (circles) around the Sun. The largest view that we can have is to look at the entire universe. Scientists often choose a certain point of view, or frame of reference, when studying physics. This allows them to study specific actions in the universe. Meter (m) Second (s) used to measure length used to measure time International System of Units (in-tur-NASH-uh-nuhl, SISS-tuhm, YOO-nitz): a standard way of measuring something force (forss): what causes something to change its speed or it’s direction of movement mass (mass): the amount of material in an object metric system (MET-rik, SISS-tuhm): a system of measurement based on tens that uses basic units such as the meter liter, and gram motion: (MOH-shuhn): when something is moving This river is in motion. Force Forces are at work everywhere. A force is anything that affects the movement or shape of an object. Objects can be so small that you ... - tailieumienphi.vn