Heat and Temperature Dr Mohammed Abdulrazzaq Mechanical Department

Heat and Temperature Dr. Mohammed Abdulrazzaq Mechanical Department

What is Heat? ? n Heat = Thermal Energy!! n Thermal Energy = the total energy of all of the particles in a material or object. n Throughout the ages people have invented a variety of devices to help create and capture heat for use.

Topic 1: Using Energy from Heat n What are some ways that we use heat? n n Cook food Warm buildings Dry clothes What are some ways Thermal Energy has been used throughout history?

Development of Heat Technologies n What heat technologies can you think of that have been developed through-out time? Why have they changed? n Examples….

Devices to generate, transfer, control or remove heat n Heat = Thermal energy n Can you think of any examples of devices that generate, transfer, control or remove heat?

Topic 2: Measuring Temperature n Thermometer: Mechanical or electrical device for measuring temperature. Early thermometer was invented by Galileo. n Scale: A series of equally measured sections that are marked and numbered for use in measurement.

Celsius Scale n Celsius Scale: Most commonly used in Canada. Unit of temperature is called a degree. Based on the boiling and freezing points of water. n Boiling Point: The temperature at which water boils. 100 o C at sea level. n Freezing Point: The temperature at which water freezes. 0 o C at sea level.

Another Scale… n n Kelvin is another way of measuring temperature. Scientists use Kelvin to explain the behaviour of gases. “Absolute Zero” is measured in Kelvin – which is the coldest possible temperature 0 Kelvin = -273 ºC

Right Device for the Job n n Each thermometer has a sensor – a material which is affected by changes in the environment (such as temperature) The sensor produces a signal (information about temperature, such as an electrical current) which affects a responder (a pointer, light or other mechanism that uses the signal in some way)

The Thermocouple n n n Wires made up of two different metals are twisted together. When the wire tips are heated, a small electric current is generated The amount of current depends on the temperature. They can measure higher temperatures than thermometers. The electric current can be used to turn switches on or off if the temperature changes. Used in kilns, diesel engines and industrial furnaces

Bimetallic Strip n n Made of two different metals joined together When the strip is heated one metal expands more than the other Thus the strip coils more tightly Movement of the strip can operate a switch that can control furnaces…commonly used in thermostats in homes

Your Brain…(extra) n n Your brain has its own temperature sensor. It monitors your own internal temperature. If the temperature outside changes, the sensor signals your brain to release chemicals that will help your body adjust to normal temperature (37°C)

Continued n Recording Thermometer: A bimetallic strip connected to a writing device and paper which records temperature fluctuations over time. n Infrared Thermogram: Records infrared radiation, (heat sensor) as different colors according to their temperature.

Topic 3: Particle Model of Matter, Temperature and Thermal Energy n n Reminder: matter is anything that takes up space Three most important ideas of the model: n n n All substances are made of particles too small to see The particles are always in motion The particles have space between them

n When motion of particles increases – so does the temperature n When motion of particles decreases – so does the temperature Temperature indicates the average speed of particle motion in a substance

Glow Stick Demonstration n n What will happen to the glow stick when it is placed in hot water? What will happen to the glow stick when it is placed in cold water?

Energy n n n Energy is the ability to do work – in other words to cause change In order for something to change, there must be a transfer of energy from one thing to another Ex. Charged batteries run your i. Pod, dead batteries would not

Thermal Energy n Energy associated with hot objects n What gives off thermal energy?

What Energy is…and is not n n Energy is not a substance. It cannot be weighed It does not take up space Energy describes a condition Law of Conservation of Energy: Energy cannot be created or destroyed. It can only be transformed from one type to another or passed from one object to another

Temperature vs. Thermal Energy n Temperature = A measure of the average energy of the particles in a material. n Thermal Energy = The total energy of all the particles in a material. What is the difference? ?

Topic 4: Expansion and Contraction n n Contract: Decrease in volume Expand: Increase in volume n Temperature changes cause things to expand contract n n Heated – usually causes expansion Cooled – usually causes contraction n Usually more drastic in gases, then liquids then solids

Topic 5: The Particle Model and Changes of State n Heat Capacity: Amount of thermal energy that warms or cools the object by one degree Celsius. n Specific Heat Capacity: Amount of thermal energy that warms or cools one gram of a material by one degree Celsius.

Sample Specific Heat Capacity Table

Solids n Solids have definite shape and volume n Cannot be compressed into smaller objects n When solids are heated – they expand When solids are cooled – they contract n

Liquids n Liquids have definite volume but no shape n Cannot be compressed (meaning if I have 1 litre of coke, I cannot make it fit into a pop can) n When liquids are heated – they expand When liquids are cooled – they contract n

Gases n Have no definite shape or size n Can be compressed n When heated, gases – expand When cooled, gases - contract n

Changes of State

Definitions: n Define, in your notes, each of the following: n Melt n Freeze n Evaporate n Condense n Sublimation

Continued n Evaporative Cooling: A process in which the faster moving particles on the surface of a liquid evaporate and escape into the air, the slower ones are left behind creating a lower average kinetic energy (cooling it) n Particles are more or less organized when they are hot or cold? ?

Phase Changing n During a change from solid to liquid or liquid to gas the average temperature does not change even though heat is being added, the name for the heat that is added is latent heat.

Topic 6: Transferring Energy n There are 3 main ways to transfer energy n n 1) Radiation 2) Conduction 3) Convection n ***See handout*** n

Transferring Energy Continued n n n Energy Source: An object or material that can transfer its energy to other objects. Radiation: The transfer of energy without any movement of matter. Radiant Energy: (a. k. a. EMR) Energy that is transferred by radiation.

Radiant Energy All forms of radiant energy share several characteristics: - They behave like waves - They can be absorbed and reflected by objects - They travel across empty space at the same high speed of 300, 000 km/s n

Conduction and Insulation n Thermal Conduction: The process of transferring thermal energy through direct collisions between particles. n Examples of good conductors? ? ? n Heat Insulators: Are very poor conductors n Examples? ? ?

Topic 7: Sources of Thermal Energy n Energy appears in many forms n Potential Energy: Stored energy n E. g. elastic pulled back and ready to be shot. n Kinetic Energy: Energy of motion n Examples? ?

Chemical Energy n Stored chemical energy is released in the form of thermal energy when it is burned.

Electrical Energy n Electricity n Example: hydro-electric dams – falling water is changed to electrical energy

Geothermal Energy n Energy that we get from the Earth’s interior

Solar Energy n Energy from the sun

Passive Solar Heating n Uses materials in the structure to absorb, store, and release solar energy. n Example: a wall of windows

Active Solar Energy n Uses mechanical devices to distribute stored thermal energy n Example: fans n Solar Collectors – use stored water or air on the roof, heats it, and then pumps it through the building

Wind Energy n n Moving air Is a result of solar energy – as the sun heats the air, the warmer air rises and cools off. Cooler air falls, creating a convection current – this forms wind

Fossil Fuels n Chemicals made from plants and animals that died and decomposed millions of years ago and have preserved deep underground.

Energy Converters n Energy can be converted into another form. n For example a candle can convert chemical energy into heat and light energy. n Candles are energy converters (devices which convert or change energy from one form to another. ) n Other examples? ?

Renewable Resources Definition: Renewable resources are a natural resource that grow at about the same rate they are used up.

Non-Renewable Resource Definition: A resource which is limited in supply and cannot be replaced once it is used.

Renewable Resources in Alberta Examples: v Trees (Forestry) v Wind (Wind Farms) v Agriculture ( One of the biggest crop producers in Canada) v Water (Dams and water conservation) v Solar ( Solar Panels and Solariums)

Non-Renewable Resources in Alberta Examples: ü Oil (Oil Wells) ü Natural Gas (Pipelines across the province) ü Coal (Mining in Alberta)

Positive and Negative Effects On Our Environment Positive (Renewable) n Plentiful n Non-polluting n Low cost to acquire n Cogeneration n n Negative (nonrenewable) Polluting – greenhouse gases, thermal pollution Expensive Can be rare Not plentiful

Greenhouse Gases – do not write down n Even though carbon dioxide occurs naturally in the environment (we breathe out CO 2 and plants require CO 2), it, like anything is only good in moderation. When there is too much CO 2 in the air, heat from Earth is unable to escape into space because it is trapped by greenhouse gases (which have a lot of CO 2 in them) – scientist believe that this leads to GLOBAL WARMING

Global Warming do not write down n When there is an increase in CO 2 and greenhouse gases are trapping thermal energy – the Earth’s temperature increases rapidly. A few degrees doesn’t seem to affect us much, but to the Earth, it can make a huge difference. It can change climate zones, plant growing abilities, dry up rivers and lakes, and even melt polar ice caps…. What are some effects on the surrounding environments if these things happen?

Cogeneration n n Sometimes negative effects can be turned into more positive effects – cogeneration uses waste from thermal pollution to produce electricity or uses the waste to heat buildings. FACT: when fuel burns in a thermo-electric power plant, only about 1/3 of its energy is converted into electricity – cogeneration is efficient because it uses some of the remaining 2/3 of energy

The Three Important Renewable Resources to me and Why? 1. 2. Water: Very important to me since I need water to survive. Water is a very good way to generate energy so that I may have electricity in my home. Agriculture: It is the most important to me since I need food to live. It provides me with produce to eat and clothes that I may wear.

Continued 3. Sun: The sun gives me energy to go to school everyday. It provides me with light so that I am not always walking around in the dark. It also makes things grow. The best part is that you can capture the sun and turn it into energy that can be used.

Renewable Resources

Lab Activity… n How else do energy resources affect our environment? In this lab we will look at how renewable resources and our environment are affected by pollution – specifically OIL SPILLS

Topic 8: Conserving Our Fossil Fuel Resources n n Insulate homes and water lines Reduce the amount of energy we use Install a programmable thermostat Carpool Others? ?