CHAPTER 1 WHAT IS HEAT eat is so well known from our ear liest childhood that we hardly think about it A steaming bowl of soup an active radiator and a sauna feel hot a book and a chocolate bar at room tem perature seem less hot and an ice cube feels cold In everyday speech it is common to say that the soup has more heat than the book and that the ice cube has less heat than the chocolate bar However people often use the word heat when what they really mean is temperature or a type of energy called ther mal energy Temperature is a measure of hotness or coldness In physics heat refers specifically to energy that is transferred from one thing to another because of a difference in tempera ture If two objects at different temperatures are brought together energy is transferred that is heat flows from the hotter object to the colder one A radiator gives off heat warming the cooler air around it If a per son holds an unwrapped chocolate bar his or her hands transmit heat to the choco late eventually melting it It is incorrect to IO
WHAT IS HEAT speak of the heat in an object itself because I heat is restricted to energy being transferred Energy that is stored in an object because of its temperature is called thermal energy It can be difficult at first to understand the difference between heat temperature and thermal energy To better understand these three related concepts it is helpful to know what actually makes things hot or cold Heat The woman's hand transmits beat to the chocolate barſ which is at a lower temperature than her hand and causes it to melt Westend61 Super Stock II
HEAT temperature and thermal energy are all con cerned with microscopic movements within matter These movements are explained by what is called the kinetic theory of matter MoLECULES IN MoTION All matter whether a solid liquid or gas is composed of tiny particles such as molecules and atoms These particles are constantly in motion traveling vibrating or rotating randomly in all directions One of the many different forms of energy is the energy some thing has because of its motion This type of energy is called kinetic energy The kinetic energy of the particles in matter is the basis of temperature thermal energy and heat Temperature is the measurement of how fast on average the particles in something are moving Microwaving a bowl of soup for example raises the temperature of the soup by speeding up the average motion of its molecules The molecules in the hot soup are traveling faster overall than they did before the soup was heated The molecules in an ice cube are moving more slowly Temperature is thus a measure of inten sity It does not depend on the quantity of matter being considered An ice chip and 12
WHAT IS HEAT A diagram of an atom with electrons orbiting a nucleus All matter is composed of atoms which although invisible to the human eye move and vibrate constantly creating kinetic energy Mushakesa Shutterstock com 13
