5 PHYSICS W H A T I S P H Y S I C S Energy Energy is everywhere Energy is the ability to do work It takes on many different forms Energy is stored inside atoms Light and sound are forms of 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 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 other’s results The three fundamental units of measurement they use are mass length and time Plants get their energy from the sun Animals get their energy from plants or from eating other animals Mass measures the amount of material in an object Length measures how long something is Time measures how long changes take Mass Length and Time 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 M O T I O N A N D F O R C E In physics the International System of Units is used to measure things This system is based on the metric system The metric system 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 Motion 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 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 cannot see them with the naked eye They can be bigger than planets Kilogram kg used to measure mass Meter m used to measure length Second s used to measure time International System of Units International System of Units in-tur NASH-uh-nuhl SISS-tuhm uhv 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 Motion and Force The water in a river is in constant motion
PHYSICS and stars Some forces pull objects together Other forces push objects apart Forces also affect people The Four Fundamental Forces There are four basic or fundamental forces in nature They are the gravitational force the electromagnetic force the strong nuclear force and the weak nuclear force These forces pass through us and exist within us They hold everything together All forces in nature are related to one of the four fundamental forces Each of these forces serves a different purpose Gravitational Force The gravitational force is the force of attraction or pulling together It is powerful enough to hold the Earth in its orbit around the sun Still it is the weakest of the four fundamental forces The gravitational force of the Earth is often called gravity Gravity keeps things on the surface of the Earth from flying off into space It keeps the ground on the Earth and your feet on the ground Everything that has mass has gravity In deep space the force of gravity is very weak This is because objects with mass are so far apart Gravitational force keeps the planets in orbit around the sun Gravity pulls this diver into the water M O T I O N A N D F O R C E 7
8 PHYSICS M O T I O N A N D F O R C E Electromagnetic Force The electromagnetic force is either an attraction pulling toward or a repulsion pushing away The electromagnetic force occurs in many forms Except for gravity most of the forces in nature are caused by electromagnetic forces Strong Nuclear Force The strong nuclear force is the strongest of the fundamental forces It only works within atoms The strong nuclear force keeps the nucleus center of an atom from coming apart It is like a glue holding the subatomic particles or smaller parts of the atom together The strong nuclear force gets weaker the further the particles are from the center of the atom Weak Nuclear Force The weak nuclear force causes the nuclei centers of some atoms to break apart These atoms are radioactive or unstable They give off tiny particles over time These are called beta particles The weak nuclear force causes the subatomic structure or smaller parts of some atoms to change This process is called radioactive decay The weak nuclear force does not happen in all nuclei Velocity and Acceleration The speed of an object is called velocity The velocity of an object is how fast it is moving at a point in time Velocity is measured in distance traveled per unit of time For example cars may drive 62 miles per hour 100 kilometers per hour Most people Small pieces of iron are attracted to the magnet electromagnetic force i-lek-tro-mag-NET-ik forss a combination of electrical and magnetic forces that attract push towards or repel push away escape velocity ess-KAPE vuh-LOSS-uh-tee how fast something needs to travel to leave the Earth’s gravity gravity GRAV-uh-tee a force that pulls things toward Earth nucleus NOO-klee-uhss center section of an atom made of protons and neutrons radioactive decay ray-dee-oh-AK-tiv di-KAY when the center of an atom breaks apart subatomic particles suhb-a-TOM-ik PART tuh-kuhls the smaller parts of an atom including the protons neutrons and electrons
