Heat and Temperature

Unit C - Heat and Temperature

Section 1 - Human needs have led to technologies for obtaining and controlling heat.

Subsection 1.1 - History of Heat Technologies Heat is the energy that is given off from the movement of tiny particles that make up all matter.

Heat technologies are technologies that use and control heat in a way that meets our needs and wants. Examples include furnaces, fireplace, microwave, freezers, winter jackets.  What are some examples of technologies from the past and how are they different from today?

Depending on our culture, we use different types of heat technologies and we use them in different ways.

The importance of heat is linked to all of our basic needs (air, shelter, water, and food). Can you explain how? If the range of temperature that we can exist at is between 0C-45C then how do we survive in the winter?

Subsection 1.2 - Heat Technologies in Everyday Life Standard of living refers to how much and what kind of technology we use daily. The more technology the higher our standard of living becomes. A resource that does not run out or an activity that we can continue for a long period of time without bad results is said to be sustainable. Can you think of some examples? Section 2 - Heat affects matter in different ways.

Subsection 2.1 - States of Matter and The Particle Model of Matter Matter is anything that has mass and takes up space. It can exist in three states or forms: a) solid b) liquid c) gas

Heat energy is a form of energy. It transfers from hotter objects to cooler ones. For example - putting your bare hand on the ice. The "cold" doesn't come into your hand the heat energy from your hand goes into the ice. The official unit of heat energy is the joule (J).

Changes of State GAS

Evaporation Condensation (100C) (100C) there are exceptions LIQUID there are exceptions

Melting Freezing (0C) (0C) SOLID Particle Model of Matter

1. All matter is made up of extremely tiny particles. 2. The tiny particles of matter are always moving. 3. Adding heat to matter makes the particles move around faster. 4. The particles have space between them. 5. There are attractive forces between the particles. As the particles gain heat energy they begin to move around faster. The spaces between the particles get larger. The attractive forces between the particles become weaker. When energy causes movement we can call it kinetic energy. So adding heat increases the kinetic energy of the particles.

Subsection 2.2 - Heat and Temperature Temperature is a measure of the average heat energy of all the particles in a substance. One of the containers below has more particles in it than the other but their temperatures are the same.

Thermal Energy is the total amount of heat energy in a substance. This time you add up the amount of heat energy each particle has. Looking at the same containers of water the larger pot has more thermal energy because it has more particles.

40C 40C

 Thermometers are used to measure temperature. We use the Celcius (C) scale in Canada. The United States uses the Fehrenheit (F) scale. C = 5(  F-32) 9

Subsection 2.3 - Heat Affects the Volume of Solids, Liquids, & Gases Volume is the amount of space something takes up. When the volume of an object increases due to an increase in thermal energy we say that it is expanding (thermal expansion). This happens because the particles are moving more, the attractive forces are weakening and the spaces between them are getting larger. If the volume decreases it is contracting. Solids, liquids, and gases all expand and contract.

Subsection 2.4 - Heat Transfer by Conduction

Heat transfers in three ways: conduction, convection and radiation. 1. Conduction is the transfer of heat energy between substances that are in contact with each other. A spoon in a cup of hot chocolate is an example of two objects in contact with each other. The heat energy of the particles in the hot chocolate (hotter object) are transferred to the particles of the spoon (cooler object). The heat energy continues to transfer from particle to particle.

Materials that allow easy transfer of heat are called conductors. Metals are good examples of conductors. Insulators are materials that do not allow the easy transfer of heat. Plastic, wood, and air are good examples of insulators.

Subsection 2.5 - Heat Transfer by Convection and Radiation 2. Convection involves the transfer of heat when liquid or gas particles move from one area to another. This occurs when the particles of a liquid or gas travel in circular patterns called convection currents. The particles in a boiling pot of water for example.

Hot Plate As the particles at the bottom of the pot heat up they become less dense and begin to rise. As they rise they loose heat, cool off, and become more dense. This causes them to move back down to the bottom of the pot of water. This creates a continual circulation of the water particles. 3. Radiation differs from conduction and convection because it does not rely on the movement of particles to transfer heat energy. Instead heat is transferred by invisible infrared waves that can travel great distances. The heat from the sun is an example of radiant heat transfer. The energy transferred in this way is called radiant energy. This energy is absorbed by dark and dull objects and reflected by shiny light coloured objects.

Section 3 - Understanding heat and temperature helps explain natural phenomena and technological devices.

Subsection 3.1 - Natural Sources of Thermal Energy

Some natural sources of thermal energy include solar energy, geothermal energy, fire, decay.  Geothermal energy is energy that originates from inside the earth. An erupting volcano or an active geyser are examples.  Fire involves the conversion of chemical energy inside fuels such as wood, oil, natural gas and coal into thermal energy.  As plants and animals decay thermal energy is released.  Solar energy is produced by nuclear reactions that occur inside the sun. Without this source of thermal energy our planet would not survive.

There are two types of solar heating: passive and active. 1. Passive system - heating directly with the sun's rays. The thermal energy wouldn't be directed or channelled to the different parts of the building. The main approach to this system is to increase heat gain and reduce heat loss. This can be done with insulation, double pained windows and positioning of windows. Can you think of some other practices that could make a passive system work more efficiently?

2. Active systems depend on a mechanical device to distribute the solar energy through the house efficiently. It includes three parts: collector, storage unit and distribution system. The illustration on page 226 of your Science in Action 7 text shows how water is used in an active system.

Solar energy can also be converted into electricity. Solar cells are arranged in panels, which traps and stores the solar energy as electricity. This electricity can then be stored in low voltage batteries. Advantages and Disadvantages of Solar Energy Advantages Disadvantages It is a sustainable resource Equipment is expensive No pollution Cannot provide ass electrical needs of a home with it No radiation Disposal of equipment could be an environmental concern Subsection 3.2 - Heating Technologies Many heat technologies in our homes are able to maintain a constant temperature (ex - iron, stove, furnace, blow dryer). This is because they contain a thermostat. The switch in a thermostat uses a bimetallic strip. When it is heated or cooled it will bend. As the strip bends it will either open or

close an electric circuit. If it breaks the circuit the appliance heats up; if it connects the circuit then it will cool down. Notice the bimetallic strip in the iron.

There are two types of heating systems: local and central. Central heating systems provide heat from a single centre or source (ex - furnace). Then it is distributed via pipes, ducts and vents to various parts of a building. It can either be forced air or hot water heating. Local heating systems provide heat for only one room or small part of a building (ex - fireplace, space heaters). In both cases convection currents are at work.

Thermal energy also helps to keep your fridge cold. As the refrigerant flows through pipes in the walls of your fridge it changes from a liquid state to a gas state. This requires heat energy, which it gets from the inside of your fridge. As the inside of your fridge looses that heat energy it gets cold. Then the gas is allowed to loose its heat out the back of the fridge and turn back into a liquid.

Subsection 3.3 - Heat Loss and Insulation Insulation keeps heat in during the winter and the cold out during the summer. The higher the R-value of the insulation the better insulator it is. Thermal conductivity of a material reflects a materials ability to transfer heat by conduction. Generally, in buildings we want a low thermal conductivity. A thermogram is an infrared photograph of a building. The colours tell us which parts of the building are loosing the most heat (highest thermal conductivity). Based on the thermogram picture on page 234, what parts of a home are the sources of greatest heat loss? Section 4 - Technologies that use heat have benefits and costs to society and to the environment. Subsection 4.1 - Looking and Different Sources of Heat

Fossil fuels were formed from the remains of plants and animals that lived millions of years ago. - they are non-renewable - easy to obtain and transport - available in large quantities - cheaper than other sources There are disadvantages to using fossil fuels. - they may be cheaper than other sources of energy but they still have a high price - using them pollutes the environment - pollution can lead to diseases in humans Wind energy is a very practical source of thermal energy in areas where it is windy. There are very few disadvantages to using this technology. Nuclear energy is obtained by using radioactive materials to produce heat. This heat can then be used to generate electricity. The disadvantage of this is the it involves the use and disposal of materials that are very harmful to living things. Hydro-Electric power is generated by water moving through a dam. As the water passes through the dam it turns large turbines, which then generate electricity. 4.2 - Energy Consumption The three main energy users are home, transportation and industry. What are some things we can do to limit the amount of energy we consume in these three areas?