NEW UNIT C HEAT and TEMPERATURE.pdf

UNIT C HEAT & TEMPERATURE SECTION 01 Human needs have Led to Technologies for obtaining and controlling heat. Needs and Wants Needs wants Standard of living Needs are the basic, required conditions that we must meet in order to live. It is necessary to our survival that we fulﬁll these needs Wants stem from needs and include ways in which needs could be met. The standard of living refers to the level of wealth, comfort, material goods, and necessities available to a particular society or individual. However, unlike needs, it is not vital to our survival that all of our wants be satisﬁed. It can be inﬂuenced by factors such as income, access to education and healthcare, employment opportunities, and overall economic conditions. 1.1 History of Heat Technology Heat Kinetic Energy thermal Energy Is the energy that transfers from a substance whose particles have a higher kinetic energy to a substance whose particles have a lower kinetic energy. Is the energy an object has as a result of its motion. Is the total kinetic energy of all particles in a substance. Example: - person walking - baseball in the air - item falling of a table Example: - warmth of the sun - heat from a heater - air in baking oven Early theories of heat 1.2 Million years ago early humans used ﬁre for to cook their food and keep warm. Empedocles (450 BC) Empedocles’ believed that all matter was made up of earth, air, ﬁre and water. He thought when objects burned, the ﬁre inside was released. Caloric theory (1600s) The caloric theory is an obsolete scientiﬁc theory that heat consists of a self-repellent ﬂuid called caloric, a massless ﬂuid, that exited in all object and ﬂows from hotter bodies to colder bodies. Caloric was also thought of as a weightless gas that could pass in and out of pores in solids and liquids. Benjamin thompson (Count Rumford) 1753 - 1814 In Germany, Count Rumford was in charge of building cannons. He discovered that when they bore the hole out of metal a great amount of heat was produced. It was at this time he theorized that heat was a form of energy resulting from friction. Julius mayer (1800s) In the 1800s, Julius Mayer was the ﬁrst to discover the relationship between heat and energy. He was employed as a ship’s doctor on trips to the East Indies. He performed “bloodletting” on sick sailors, as it was believed this would cure them. He noticed that the blood of the sailors was darker red than that of the native populations in warmer climates. Julius mayer (1800s)..... Julius found that the sailors, being from northern colder climates, had less oxygen in their blood resulting in a darker red colour. The reason was this was that it had to work harder to keep the body warmer. Before Julius could write about his ﬁnding, the discovery between energy and heat was published by a famous scientist……… James Prescott Joule James prescott joule (1800s) He came up with the mechanical equivalent of heat, called the JOULE (J). Joule's apparatus for measuring the mechanical equivalent of heat. A descending weight attached to a string causes a paddle immersed in water to rotate and the "work" of the falling weight is converted into "heat" by agitating the water and raising its temperature. After further investigations and observations... Scientists decided that heat was not a substance, but a form of energy, that comes from the movement of tiny particles. 1.2 Heat Technologies in Everyday Life In addition to being able to produce heat to meet human needs and wants. It is also important to be able to control that heat. As technologies develop to generate heat, ways to direct and manage that heat have also been created. Making sustainable choices sustainable Sustainable means that something can be maintained or continued. When we talk about sustainable use of resources, we mean that we are trying to use our resources wisely and do as little damage as possible to the environment when we use them. SECTION 1 QUIZ SECTION 02 Heat Effects Matter in Different Ways Particle model of matter The Particle Model of Matter is used to explain what happens to matter when energy is added or removed. 1 All matter is made up of extremely tiny molecules They are much too small to see except with powerful, magnifying instruments, called electron microscopes. 2 The tiny particles of matter are always moving This movement involves a form of energy known as kinetic energy. Each particle of matter has kinetic energy—energy of movement. 3 Adding Heat Makes the Particles Move Faster Faster-moving things have more kinetic energy. So adding heat increases the kinetic energy of the particles. 4 The particles have space between them Different states of matter have different amounts of space between the particles. 2.1 States of Matter and The Particle Model of Matter Everything in the universe is made up of matter. Matter exists in four states: solid, liquid, gas and plasma. One way that heat can affect matter is by causing a change of state. This happens by adding or taking away heat energy. Heat (Thermal) Energy is a form of energy that transfers from matter at higher temperatures to matter at lower temperatures. Phase Changes When heat is added or removed matter goes through phase changes. Why is the Particle model of matter important 1 2 3 In chemical reactions, understanding the behavior of particles can help predict how different substances will interact with each other. In physics, knowledge of the particle model of matter is crucial for understanding how energy and momentum are transferred between particles in collisions. In engineering, understanding the behavior of particles can help design materials with speciﬁc properties, such as strength, ﬂexibility, or conductivity. Solid How heat affects particles As heat is applied to a solid, the particles begin to move faster and further apart until they become a plasma. Liquid i An n io t ma Gas Plasma The interaction and collision of molecules within a liquid, gas, or plasma is called Brownian Motion. 2.2 Heat vs. Temperature Temperature A measure of how hot or cold matter is. Recall that heat energy transfers from hotter substances to colder ones. If you put a pot of soup on a hot stove burner, the soup will slowly heat up. Thermal Energy The total kinetic energy of all the particles the substance contains. Think about your soup example again. You heat the soup in a pot, and then pour a small amount of it into a cup. The temperature of the soup is the same in the pot and in the cup. But the soup in the pot has more thermal energy than the soup in the cup. This is because the amount of soup in the pot is greater than the amount of soup in the cup. A larger amount of soup contains more particles. Understanding the Difference Thermal Energy Thermal energy is the total kinetic energy of all the particles in a substance. An example is the pot of soup. Heat Heat is the energy that transfers from a substance whose particles have a higher kinetic energy to one whose particles have lower kinetic energy. An example is boiling water. Temperature Temperature is a measure of the average kinetic energy of the particles in the substance. Understanding the Difference Heat ﬂows spontaneously from hotter objects to colder objects. This is because heat is a form of energy that is transferred from one object to another as a result of a temperature difference between them. When two objects are in contact, the molecules of the hotter object have more kinetic energy than those of the colder object. As a result, the hotter object transfers heat to the colder object until both objects reach thermal equilibrium, which means they have the same temperature and therefore the same kinetic energy. 2.3 Heat Affects the Volume of Solids, Liquids, and Gases What Happened? With a partner, develop a theory on what has occurred in each of the following situations. Scenario 1 A large area of concrete is poured as a single slab to create a new outdoor basketball court for your school. The work is done in August before the new school year starts. A very cold winter follows. When spring comes and you and your friends want to use the court, you notice several large cracks in the concrete. It looks like the concrete will need replacing. What Happened? Scenario 1 The large cracks in the concrete on the outdoor basketball court could be due to various factors, such as the rapid moisture loss, also known as "plastic shrinkage," that occurs before the concrete dries. During the pouring phase in August, the concrete may have been exposed to hot and dry conditions, causing the moisture to evaporate quickly and resulting in cracks. Additionally, the very cold winter that followed could have contributed to the cracking. Concrete can contract in cold temperatures, and if it lacks proper contraction joints, the stress from the contraction can lead to cracks. These cracks often occur because of the evaporation of excess mixing water and the shrinkage of the concrete as it cures and dries Scenario 2 A student is ﬁxing his bike and he places one bolt in the sun and the other in the shade. He left for a few hours and upon returning could turn on the bolt left in the shade, however, the bolt left in the sun would not turn on properly. What happened? Scenario 2 When two different metal objects are exposed to heat, they expand at different rates. In this scenario, the metal bolt and the two metal nuts (one in the shade and one in the sun) experienced thermal expansion as they were exposed to the hot summer afternoon. Metal expands when heated because the heat energy causes the atoms in the metal to vibrate more vigorously, resulting in increased spacing between the atoms. The metal bolt was directly exposed to the sun, causing it to absorb more heat compared to the nut in the shade. As a result, the bolt expanded more than the nut. Scenario 3 After getting caught in a summer thunderstorm, you decide to make yourself a mug of hot chocolate. The biggest mugs are in your kitchen freezer, chilled and ready for lemonade on the next hot day. You take one, noticing that the thick glass is covered with a light layer of frost. As you pour the boiling water into the mug, you hear and see it crack. What Happened? Scenario 3 Materials undergo thermal expansion when heated and contraction when cooled. When you took the chilled mug out of the freezer and poured boiling water into it, it was subjected to sudden and extreme temperature changes. The hot water caused the inside of the mug to expand rapidly, while the frozen outside of the mug remained constricted[1]. This rapid temperature change causes a strain on the glass, leading to the crack that you observed. Expansion & Contraction of Solids The particle model of matter tells us that when the thermal energy of a solid increases, so does its volume. We say that the solid expands. This occurs when heat transfers to a solid. When the thermal energy of a solid decreases, its volume decreases, and the solid contracts. This occurs when heat transfers from the warmer solid to cooler matter. Thermal expansion can be deﬁned as the change in the length, width, height, or volume of any material on changing the temperature. Thermal expansion is very evident in solids as atoms are densely packed. Expansion & Contraction in Liquids & Gases We can see a simple example of expansion and contraction of a liquid in the thermometer. Liquid, usually alcohol, is placed in a narrow glass tube. As the liquid becomes warmer, it expands and rises in the glass tube. As it cools, contraction takes place and the liquid drops down. Similar principles are at work when there is a change in the heat energy of a gas. It is a very cold night, and you walk quickly. The farther you go, the more the balloons seem to be “wilting.” They no longer pull at the ribbons, but now bob near your shoulders. By the time you reach home, the balloons are noticeably smaller and look a bit wrinkled. However, after they have been in your bedroom for an hour, the balloons are in the same condition as when you left the party. Both contraction and expansion have been at work! 2.4 Heat Transfer by Conduction Conduction Conduction is the transfer of heat energy between substances that are in contact with each other. The particles in the hot chocolate are moving rapidly, and they bombard the particles in the parts of the spoon that are in the hot liquid. The spoon’s particles that are being pushed around start to move faster, vibrating back and forth. The faster they move, the greater the thermal energy in that part of the spoon. The spoon begins to warm up. The parts of the spoon that are not in the hot chocolate become warm because of the movement of other particles within the spoon. The fast moving particles in the part of the spoon that had been warmed by the hot chocolate now bump into their neighbours in the spoon’s handle. These particles speed up and bump into those next to them. And so on, until all the particles in the spoon are moving faster. Conductors & Insulators Conductors One of the key characteristics of conduction is that heat transfers in only one direction—from areas of greater kinetic energy to areas of less kinetic energy. That is, heat transfers from areas having more thermal energy to areas having less thermal energy. Conduction is most common in solids. It is less common in liquids, and it is rare in gases. Materials that allow easy transfer of heat are called conductors. Conductors Conduction of heat occurs: - from one molecule or atom to another (one to one) - the molecules do not move themselves - occurs mostly in solids, some liquids, rarely gases - is the result of agitation between molecules due to an increase in heat. Insulators Insulators are materials that do not allow easy transfer of heat. They reduce the amount of heat that can transfer from a hotter object to a colder one. Insulators have a high resistance to the transfer of heat due to the design of their molecules. 2.5 Heat Transfer by Convection & Radiation Convection Another way that heat transfers through matter is by convection. In convection, heat is transferred when liquid or gas particles move from one area to another. Recall that in conduction, the particles do not move—only the heat does. In convection, the particles themselves move. For this reason, convection occurs only in liquids and gases. Heat transfer by convection occurs when the particles in a liquid or gas move in circular patterns called convection currents. Convection Currents Heat ﬁrst transfers to the bottom of the pot from the hot burner by conduction. Heat transfers from the heated bottom of the pot to the water that is in direct contact with it. The kinetic energy of the water particles increases. They move faster and spread farther apart. In other words, the water at the bottom of the pot expands. As the water expands, it becomes less dense and rises up to the surface. The particles in the rising warm water push the cooler particles at the top aside. This cooler water sinks toward the bottom of the pot to ﬁll the space left by the rising warm water. When the cooler water reaches the bottom, it too heats up and expands. It rises, leaving space for more water from the top to sink downward. This sets up a circular convection current. As long as heat continues to transfer from the hot burner, this pattern of convection currents continues to transfer heat throughout the water. Convection Currents in Air As with conduction, heat transfers by convection move in only one direction. It moves from an area of greater kinetic energy to one of lesser kinetic energy. Think about being in a cold room that has a heater in one corner. When the heater is first turned on, the only part of the room that is warm is the space closest to the heater. As the air near the heater heats up, it expands, becomes less dense, and rises. Cooler air moves in to take its place near the heater. This air is then heated, and it rises. Convection currents form, and eventually the entire room becomes warm. Convection Currents and Energy Efﬁcient Windows The problem with the old storm windows was that they weren’t very efficient. They still lost a lot of heat because convection currents would form in the air space between the panes of glass. The convection currents would transfer heat from one pane of glass to the other. Energy efficient windows are designed to reduce heat transfer. They do this by preventing convection from occurring between the panes of glass. Winter: Heat from inside the house moves to the colder environment outside, resulting in heat loss. Summer: Heat transfers through the single pane window, heating your house. The space in between is filled with a gas, argon (cheaper) or krypton to assist in insulation. Summer: Allows only 10 percent of heat to pass into the home. Winter: Allows only 10 percent of the heat to pass out through the window. The two spaces in between is filled with a gas, argon (cheaper) or krypton to assist in insulation. Summer: Allows only 3 percent of heat to pass into the home. Winter: Allows only 3 percent of the heat to pass out through the window. Heat Transfer by Radiation Radiation is the transfer of energy by invisible waves that can travel great distances. It does not rely on the movement of particles for heat transfer. Energy transferred from its source by radiation is called radiant energy. Heat is only one type of radiant energy. It is transferred by invisible waves called infrared waves. When the invisible radiant energy waves come in contact with an object, the particles in the object increase in kinetic energy. The particles move faster and the object becomes hotter. Reﬂect or Absorb Matter can reﬂect or absorb radiant energy. Objects that are shiny and light coloured are good reﬂectors of radiant energy. So on a hot, sunny summer day, to stay cool, you would probably choose light coloured clothing. Dark and dull objects are good at absorbing radiant energy. If you have been on a black sand beach such as those found in parts of Europe, the Caribbean, or the South Paciﬁc, on a sunny day, then you know just how good dark colours are at absorbing radiant energy! At the hottest point in the day, the skin on the soles of people’s feet will begin to burn if they run barefoot over a long stretch of sand. WHat is the Best conductor / insulator STEM ACTIVITY Design a cocoa cup SECTION 2 QUIZ SECTION 03 Understanding heat and temperature helps explain natural phenomena and technological devices. 3.1 Natural Sources of Thermal Energy (heat) thermal Energy Is the total kinetic energy of all particles in a substance. Example: - warmth of the sun - heat from a heater - air in baking oven Sources of thermal energy Solar Energy Geothermal Energy Decay Fire Passive Solar Heating Solar energy Passive Solar Heating Passive Solar Heating means that the system simply lets the radiant energy from the sun to come into the home and prevents heat from escaping. A southern exposure maximizes sunlight to the greenhouse during the winter when it is needed the most, and the home shelters it from the northern arctic blasts. Solar energy is clean and is guaranteed not to run out. It is not available all the time (night-time, less in winter/ than in summer). There are two techniques that can help to overcome these issues, passive and active solar heating. Active Solar Heating There are two basic methods of harnessing active solar energy: - solar thermal systems - solar electric systems The solar thermal systems convert the radiant energy of the sun into heat, and then use that heat energy as desired. The solar electric systems (solar array) converts the radiant energy of the sun directly into electrical energy, which can then be used as most electrical energy is used today. In a prairie climate, a combination of passive and active solar systems can usually meet up to 75% of a family’s heating needs. Solar energy Solar Thermal Systems Energy from the sun heats the cold water from a storage tank. The heated water is placed into another section of the tank and is used to circulate through pipes in the ﬂoor to heat the house by convection currents. The system has three parts: 1. 2. 3. a collector a heat storage unit heat distribution system Solar Electric Systems Solar cells are arranged in panels which are connected to form a solar array. A series of these solar arrays are then placed so as to capture and store the sun’s energy in low voltage batteries. 3.2 Heating System Technologies thermostats In order to live comfortably we have heating systems controlled by thermostats. Thermo means “heat” Stat means “keep the same” A thermostat uses a bi-metal strip, when heated one of the metals bends opening and closing an electrical circuit that turns a furnace on or off. Traditional Digital New Generation Heating Systems There are two types of heating systems: local heating systems central heating systems Local heating systems provide heat for only one room or a small part of a building. Central heating systems provide heat from a single, central source such as a furnace. The heat transfers through a network of pipes, ducts, and vents or openings in different places around the building. There are three types of central heating systems: - Forced Air Heating Hot Water Heating Radiant Floor Heating Forced Air Heating Hot Water Heating Radiant Floor Heating In a radiant setup, the warmth is supplied by hot-water tubes or electric wires buried underneath the ﬂoor. As the invisible waves of thermal radiation rise from below, they warm up any objects they strike, which radiate that captured heat in turn. 3.3 Heat Loss and Insulation insulation When building a house, you want materials that are good insulators, not conductors. Stone and brick walls are good insulators. However, these can be very expensive, and many people choose to have a layer of Styrofoam panelling between the outer walls and the siding of their homes. You want to build a house with materials that have a low thermal conductivity - the higher the thermal conductivity, the greater the heat transfer. r-value Every insulator is given a number called an R-value. The higher the R-value, the better the product is at providing insulation. Heat loss Contractors can use infrared photography to “diagnose” the areas of heat loss in a building. This kind of photo is called a thermogram. Heat loss DESIGN CHALLENGE How can you design and build a device to prevent an ice cube from melting? 1 Work by yourself or in a small group. What ideas do you have to solve the problem? Brainstorm a list of possibilities and then choose the best idea. 2 Create a plan for how you will build your device. Make sure to include a detailed sketch of your device and a list of the materials and equipment you will need. Have your teacher approve your plan before you start to build it. 3 Build your device. Test it. Do you need to make any changes to your device? Do so now. Retest your device if necessary. 4 Compare your device with those of your classmates. How successful were their devices?

NEW UNIT C HEAT and TEMPERATURE.pdf

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