he sting we feel after touching a hot pan the welcome reliefоf a cold drink on a warm day and the comfort of a heater as it thaws our frozen limbs are sensa tions that are familiar to most of us indeed hotness and coldness texture a number of our everyday experiences We may throw around terms such as heat and temperature casually in conversation to describe what we perceive in such situations but physics shows us that these are not interchangeable terms As you will discover in these pages we must begin at the atomic level of matter to understand heat and the related concepts of temperature and thermal energy as well as the relationships between them In physics the term heat refers to the energy that is transferred from a warmer object to a colder one The energy that is transferred must of course come from some where In fact it all starts with the atoms and molecules that compose all matter Each of these particles is constantly moving and gen erating energy from this motion This is called kinetic energy The total amount of kinetic energy an object has is equal to its thermal energy that is the energy that an object has stored as a result of its temperature To
INTRODUCTION illustrate let's consider a pot of soup and a cup of soup ladled from it The thermal energy of the pot is greater because it has more particles that are moving and creating energy Temperature represents the average speed of all the particles in an object the faster its particles move the higher its tem perature will be Unlike thermal energy temperature does not depend on the quan tity of the substance In the case of the pot and cup of soup the average speed of the particles may be the same in both thus giv ing them the same temperature even though they differ in size In most instances when heat is trans ferred from a warmer substance to a colder one the temperature of the warmer sub stance will decrease while that of the colder one will increase This will continue until the two are at the same temperature At other times however heat transfer may not cause a change in temperature at all rather the mol ecules of the heat absorbing substance may change and rearrange themselves in what is called a phase change One example of this is the change of water to vapor as it is heated Both temperature and heat can be mea sured The Fahrenheit and Celsius
HEAT named after Daniel Gabriel Fahrenheit and Anders Celsius respectively are perhaps the most commonly known and are frequently used on temperature measuring instruments called thermometers Heat changes in a phys ical or chemical reaction can be measured with a device called a calorimeter Anders Celsius for whom the Celsius temperature scale is named Science Source Photo Researchers
INTRODUCTION The process of heat transfer can occur througha few different methods Conduction is heat transfer between adjacent parts of a body or through direct contact between two bodies Convection transfers heat by move ment of a heated fluid such as air or water In contrast heat transfer through radiation requires neither contactnoramedium to carry the energy In this process energy is emitted radiated by a heated surface and travels to another surface where it is absorbed Heat transfer usually involves some combination of all three of these processes The relationships between heat other forms of energy temperature and work form the basis of thermodynamics The three basic laws of thermodynamics describe the nature of these relationships and hold true for all biological and physical systems Indeed much of our understanding of the universe is informed in part by thermodynamics Although we may only think about heat incidentally heat is always around us in one form or another It is critical to all life and our ability to tackle issues in such areas as climate change biology and technology rests on our application of the fundamental concepts you will encounter in this
