Chapter 12: Thermal Energy - dentonisd.org

1 PerpetualMotion?The engine converts thechemical Energy storedin the fuel and oxygeninto kinetic we ever invent anengine that converts allthe Energy into usefulenergy of motion? Look at the text on page 290 for the Chapter 11, you learned that one of the forms of Energy isstored Energy . Energy can be stored in several ways. Yourbody stores Energy as sugar in your body s cells. Some heatingsystems store Energy in hot-water tanks. A battery stores chemicalenergy released when a circuit is completed. In the last Chapter , yousaw that a compressed spring can store converting stored Energy into mechanical Energy , an object,such as this racing car, can gain kinetic Energy . However, it takesmore than the elastic potential Energy of a compressed spring toaccelerate this high-tech racing car.

2 It takes the Energy stored inthe fuel combined with the oxygen in the air to get the car tomove faster than 350 km/h (217 mph) in a few Chapter 10, you learned that work could transfer energyfrom the environment of a system. In this Chapter , you ll learnabout another way to transfer Energy the way that has transformedthe lives of people everywhere. The steam engine, the first invention that produced mechanicalenergy from fuel, transformed the United States from a society offarms to one with many factories in the 1800s. The steam enginecan be called a heat engine because it converts heat into work. Inthe case of the steam engine, the fuel source is outside the engine. However, you are probably much more familiar withheat engines that burn fuel inside the engine internal com-bustion engines.

3 One of these, the gasoline engine, precipitatedtremendous changes in the way people traveled, worked, and , more than a century after its invention in 1876 by NikolausOtto in Germany, the gasoline engine is firmly entrenched in our society. ThermalEnergyWHAT YOU LL LEARN You will define temperature. You will calculate heat transfer. You will distinguish heatfrom IT S IMPORTANT Thermal Energy provides theenergy to keep you warm, toprepare and preserve foodand to manufacture many ofthe objects you use on adaily basis. CHAPTER273 PHYSICSTo find out more about thermalenergy, visit the Glencoe ScienceWeb site at went through a Little Ice Age in the 1600s and1700s, when temperatures were lower than any other periodduring the previous one thousand years. Keeping warm was vitally important,and many people devoted themselves to the study of heat .

4 One result wasthe invention of machines that used the Energy produced by burning fuel todo useful work. These machines freed society from its dependence on theenergy provided solely by people and animals. As inventors tried to makethese machines more powerful and more efficient, they developed the sci-ence of thermodynamics,the study of makes a hot body hot?Internal combustion engines require very high temperatures to oper-ate. These high temperatures are usually produced by burning the effects of fire have been known since ancient times, only inthe eighteenth century did scientists begin to understand how a hot bodydiffers from a cold body. They proposed that when a body is heated, aninvisible fluid called caloric is added to the body. Hot bodies containmore caloric than cold bodies.

5 The caloric theory could explain observa-tions such as the expansion of objects when heated, but it could notexplain why hands get warm when they are rubbed the mid-nineteenth century, scientists developed a new theory toreplace the caloric theory. This theory is based on the assumption thatmatter is made up of many tiny particles that are always in motion. In ahot body, the particles move faster, and thus have greater kinetic energythan particles in a cooler body. This theory is called the kinetic-molecular model of a solid shown in Figure 12 1can help you understandthe kinetic-molecular theory. This model is a solid made up of tinyspherical particles held together by massless springs. The springs repre-sent the electromagnetic forces that bind the solid together.

6 The parti-cles vibrate back and forth and thus have kinetic Energy . The vibrationscompress and extend the springs, so the solid has potential Energy aswell. The overall Energy of motion of the particles that make up anobject is called the Thermal energyof that object. Thermal Energy and TemperatureAccording to the kinetic-molecular theory, a hot body has more ther-mal Energy than a similar cold body, shown in Figure 12 meansthat, as a whole, the particles in a hot body have greater Thermal energythan the particles in a cold body. It does not mean that all the particles inOBJECTIVES Describethe nature ofthermal Energy . Definetemperature anddistinguishit from thermalenergy. Use the Celsius and Kelvintemperature scales andconvertone to the other. Definespecific heat andcalculateheat andThermal Energy274 Thermal EnergyFIGURE 12 1 Molecules of asolid behave in some ways as if they were held together body have exactly the same Energy .

7 The particles have a range of energies,some high, others low. It is the averageenergy of particles in a hot bodythat is higher than that of particles in a cold body. To help you understandthis, consider the heights of students in a twelfth-grade class. The heightsvary, but you can calculate the average height. This average is likely to belarger than the average height of students in a ninth-grade class, eventhough some ninth-graders might be taller than some can you determine the hotness of an object? Hotness is aproperty of an object called its temperature,and is measured on a def-inite scale. Consider two objects. In the one you call hotter, the particlesare moving faster. That is, they have a greater average kinetic the temperature is a property of matter, the temperature doesnot depend on the number of particles in the object.

8 Temperature onlydepends on the average kinetic Energy of the particles in the object. Toillustrate this, consider two blocks of steel. The first block has a mass of1 kg and the second block has twice the mass of the first at 2 kg. If the1 kg mass of steel is at the same temperature as a 2 kg mass of steel, theaverage kinetic Energy of the particles in the both blocks is the same. Butthe 2 kg mass of steel has twice the mass and the total amount ofkinetic Energy of particles in the 2 kg mass is twice the amount in the1 kg mass. Total kinetic Energy is divided over all the particles in anobject to get the average. Therefore, the Thermal Energy in an object isproportional to the number of particles in it, but its temperature isnot, as is shown in Figure 12 and ThermometryHow do you measure your temperature?

9 If you suspect that you havea fever, you may place a thermometer in your mouth and wait two orthree minutes. The thermometer then provides a measure of the tem-perature of your are probably less familiar with the microscopic process involved inmeasuring temperature. Your body is hot compared to the thermometer,which means that the particles in your body have greater Thermal energyand are moving faster. The thermometer is made of a glass tube. When thecold glass touches your hotter body, the faster-moving particles in yourskin collide with the slower-moving particles in the glass. Energy is trans-ferred from your skin to the glass particles by the process of conduction,the transfer of kinetic Energy when particles collide. The Thermal Energy ofthe particles that make up the thermometer increases and, at the sametime, the Thermal Energy of the particles in your skin decreases.

10 As the par-ticles in the glass become more energetic, they begin to transfer energyback to the particles in your body. At some point, the rate of transfer ofenergy back and forth between the glass and your body will become equaland both will be at the same temperature. Your body and the thermome-ter are then in Thermal is, the rate at which energyflows from your body to the glass is equal to the rate at which Energy Temperature and Thermal Energy275100 mL50 mL0908070605040302090807060504030100 Cold bodyHot bodyKHot > KColdFIGURE 12 2 Particles in a hotbody have greater kinetic andpotential energies than particlesin a cold 12 3 Temperature doesnot depend on the number ofparticles in a the glass to your body. Objects that are in Thermal equilibrium are atthe same temperature, as is shown in Figure 12 thermometeris a device that measures temperature.