Transcription

1

2

3

4

5

6 Since ancient times, people have needed thermal energy (heat) to cook their food and to keep them warm. And since the beginning of time, uncontrolled heat has scorched and spoiled the taste of food and has destroyed buildings and homes. In what ways have humans made thermal energy work for them? Look at the following photographs to see some of the ways in which this form of energy has been used throughout history.

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24 Topic 2 : Measuring Temperature A relative idea about temperature is that it tells you how hot or cold something is. This can be done by using our senses: Touch - sensitive nerve endings on your skin can detect changes in temperature Sight - the color of the material giving off heat Relative ways to determine the temperature are not always reliable or safe.

25 The record Canadian low temperature of C was recorded at Snag, in the Yukon Territory. The Canadian record high temperature of 45 C was recorded in Sweetgrass, Saskatchewan.

26

27 Early thermometers (like the one Galileo invented) did not have any scale (markings with numbers) to determine precise temperature.

28

29 The 1st precise scale was developed by Anders Celsius in He used 'degree' as the unit of temperature. All of his standards for comparison to make his markings (on his scale) were based on the properties of water. 0 o was assigned the temperature at which ice melts at sea level 100 o was assigned the temperature at which liquid water boils at sea level The region between (above and below, as well) these two extremes was separated into 100 equal units (degrees) The two fixed temperatures that Celsius chose can be used to calibrate a thermometer

30

31

32 Digital Thermometer

33 It takes less time to make a mug of hot chocolate on top of a mountain. Water boils at lower temperatures the farther above sea level you go

34 Pressure also affects the freezing and boiling points of water. Extremely high pressure can cause ice to melt at a temperature below 0 o C Low pressure enables water to boil at a temperature below 100 o C On top of Mt. Everest, water boils at 69 o C Absolute zero is the coldest possible temperature o and is used by scientists. The Kelvin scale was developed by William Thomson - a.k.a. Lord Kelvin and the markings on the scale are not called degrees, but are simply called kelvins. 0 o Celsius is equal to o Kelvin o Celsius is 0 o Kelvin

35

36 This Morning Glory Pool is heated by energy from deep within the earth. The water remains about 95 C even during the winter

37 O L A D I K C O Q J B H G F E M R N

38 The Right Device for the Job Measuring different extremes of temperatures means using different types of devices to measure these extremes. Each of the following thermometers have: A sensor - a material which is affected by changes in some feature of the environment, such as temperature A signal - provides information about the temperature, such as an electric current A responder - which indicates the data with a pointer, light or other mechanism using the signal

39 Thermocouple Two wires of different metals are twisted together. When heat is applied to one end an electric current is produced. The amount of current depends on the temperature and the type of wires. This current can turn on and off a switch or valve.

40 The Bimetallic Strip A bimetallic strip is made of two different metals joined (fused) together, often formed into a coil. When heat is applied to the end, one of the metals will expand faster than the other and the coil can operate a switch or valve just as the thermocouple does.

41 The Recording Thermometer When a bimetallic coil strip is attached to a long arm lever, with a marker at the end and a drum that has graph paper, a recording thermometer can be made. This instrument works much the same as a seismograph.

42

43 The Infrared Thermogram If an object is warmer than absolute zero it gives off infrared radiation (IR). The infrared radiation can be photographed with special films or detected by special sensors that display colored images. The brightness or color of the image indicates the temperature of the object.

44

45

46 1. Suppose that you were present on the hottest day ever reported in Canada. (a) What would your body temperature have been? 37 C (b) If the air temperature had dropped by 5 C, would you have felt warm or cold? 37 warm it would still be warmer than body temperature 2. Describe how a thermostat controls the temperature in a building. A sensor senses the temperature in the building A signal - provides information about the temperature. A responder will send a signal to turn the furnace on or off depending on the temperature of the building and what it is set at.

47 3. Apply What might be the advantages and disadvantages of using a thermocouple instead of a regular lab thermometer? It can withstand hotter and colder temperatures 4. Apply Many household appliances, such as irons, are heated electrically. They usually contain a thermostat that switches electricity on and off to keep the appliance at a constant temperature. Think of at least three examples of other appliances that might use thermostats to switch electricity on and off. Hair straightener Sandwich maker Waffle iron Ice maker

48 Gas Liquid Solid Particles have lots of space between them Particles can slip past each other Particles are closely packed together

49 The Particle Model of Matter is a scientific description of the tiny particles that make up all things. The key elements in this model are: All substances are made of tiny particles too small to be seen (there are in 1 water droplet) The particles are always in motion The particles have spaces between them

50 gas liquid solid assumes the shape and volume of its container particles can move past one another takes the shape of the part of the container which it occupies particles can move/slide past one another retains a fixed volume and shape rigid - particles vibrating in place compressible not easily compressible not easily compressible lots of free space between particles little free space between particles little free space between particles flow easily past each other, move in all directions, do not flow to the lowest possible level can be poured (always flowing to the lowest possible level) and form a level (flat) surface at rest form a pile when they are poured (the particles do not continue to flow apart from each other)

51

52 Temperature and the Particle Model When heat is added to a substance, the particles move faster. When heat is lost from a substance the particles move slower. The motion of the particles increases when the temperature increases. The motion of the particles decrease when the temperature decreases Temperature indicates the average energy (speed) of the particles in motion in a substance.

53 What is Energy? Energy is the measure of a substance's ability to do work - or cause changes. Try to describe three features of the next three diagrams What has high energy? What has low energy? What change is being caused as energy is transferred? What sources provide energy for the change? To what is the energy transferred?

54

55

56 Hot-air balloons, ovens, a hot tub - these and many other devices are designed to release and transfer thermal energy (energy associated with hot objects). The fuel in a hot-air balloon burns, transferring thermal energy to air, which warms, expands, and lifts the balloon. Hot metal elements in an oven transfer thermal energy to food, warming and cooking it. Hot water in a hot tub transfers thermal energy to people in the tub.

57 There are two important elements that occur: 1. Changes happen when there is a difference of energy Every useful energy system has a high-energy source that powers the changes 2. Energy is always transferred in the same direction: From a high-energy source (hot) to something of lower energy (cold).

58 Energy is measured in joules (J), in honour of James Joule ( ), an amateur scientist who devoted his life to studying energy. To investigate the connection between energy and temperature changes, Joule built many ingenious devices. One was a set of paddle wheels that stirred water as they were turned by falling weights. The temperature of the water increased a small, but measurable, amount. If you have a sensitive computerized temperature probe, you could repeat Joule s experiment using an electric mixer or a blender to stir the water.

59 The term "thermal energy" has a precise scientific meaning, but it is not used very much in everyday language. Scientists sometimes use the word "heat," but they give it a specific meaning: thermal energy being transferred because of temperature differences. To avoid confusion, this textbook uses the scientific terms "thermal energy' and "energy transfer" whenever possible.

60 Thermal Energy and Temperature Changes When heat is transferred in a space the average energy of the particles - the temperature of the substance - is affected, by increasing or decreasing. The change in temperature depends on the number of particles affected.

61 Potters need to check the very high temperatures inside the kilns that bake and harden their pottery. To do this, they use small ceramic pyramids called 'pyrometric cones like the ones shown in the photograph. Sets of four cones are placed in the kiln along with the pottery being fired. Two of the cones soften and bend over as the kiln heats up. The third cone bends at the desired temperature. If the fourth cone bends, the kiln has overheated and the pottery may be damaged. Potters refer to cones by code numbers. For example, a number 022 cone bends at 585 C, a number 1 cone bends at 1125 C, and a number 26 cone bends at 1595 C.

62 What Energy is and is NOT Energy is not a substance. It cannot be seen, weighed or take up space. Energy is a condition or quality that a substance has. Energy is a property or quality of an object or substance that gives it the ability to move, do work or cause change. The Law of Conservation of Energy states that: Energy cannot be created or destroyed. It can only be transformed from one type to another, or passed from one object, or substance to another.

63 Topic 3 - Review 1. List the main points of the particle model of matter that were presented in this section. The key elements in this model are: All substances are made of tiny particles too small to be seen The particles are always in motion The particles have spaces between them 2. Why is it so hard to test the particle model to see if it is correct? It is hard to test the particle model because the particles are too small to be seen.

64 3. Name an important discovery or idea contributed by each of these scientists. (a) James joule Energy is measured in joules (J), in honour of James Joule ( ), an amateur scientist who devoted his life to studying energy - the connection between energy and temperature changes. (b) Anders Celsius The Celsius Thermometer (c) Lord Kelvin The Kelvin scale was developed by William Thomson - a.k.a. Lord Kelvin and the markings on the scale are not called degrees, but are simply called kelvins. 0 o Celsius is equal to o Kelvin

65 14. How is thermal energy different from temperature? Thermal energy is the energy generated by the movement or vibration of particles kinetic energy Temperature is the average energy of particle how hot or cold something is. An increase in thermal energy will cause a temperature increase. 6. Modern scientists do not use Lavoisier's "caloric fluid" theoryif this theory is wrong, why do you suppose it is discussed in many science textbooks? Antoine Lavoisier ( ) believed that an invisible substance called caloric fluid caused changes in temperature. Fires, for example, had a lot of caloric fluid, so they were hot. If caloric fluid moved from a fire to a cooking pot, the pot warmed up. For many years, scientists tried to detect and mea- sure caloric fluid. No one could. Finally scientists stopped looking for it and abandoned Lavoisier s theory. It is important because of the term calories - the quantity of heat required to raise the temperature of 1 gram of water by 1 C