Heat

How can we use this topic? Fire Inspector Safety Inspector Thermal Engineer Researcher Welder Barista Renewable Energy Engineer Energy Analyst

S2 Science Heat New Learning Revision I can use my knowledge of the different ways in which heat is transferred between hot and cold objects and the thermal conductivity of materials to improve energy efficiency in buildings or other systems. SCN 3-04a Revision By considering examples where energy is conserved, I can identify the energy source, how it is transferred and ways of reducing wasted energy . SCN 2-04a

Starter What is heat? Think, pair, share (2 mins) How do we get heat? Where does it come from?

Lesson 1: Cooling down What is heat and what is temperature? How does heat move from one place to another? What cools more quickly – a hot or a cold object? What cools more quickly – a large or a small object?

What is temperature? Temperature tells us how hot an object is Temperature is measured in degrees Celsius oC A Thermometer measures Temperature Anders Celsius (1701 – 1744)

What is heat? Heat (like light) is a form of ENERGY Heat energy Heat (like light) is a form of ENERGY All energy is measured in Joules (named after James Joule) A joulemeter measures energy. James Joule (1818 – 1889)

What is cooling? When a substance loses heat energy, it cools down and its temperature drops. Hot objects lose heat energy to colder surroundings. Heat

100 90 80 70 60 50 40 30 20 10 Temperature OC 2 4 6 8 10 12 14 16 18 20 Time in minutes

Cooling Curves Eventually, a hot object will cool down to the same temperature as its surroundings. This is usually room temperature. Comfortable room temperature is usually around 20oC So, a hot object will only cool down to this temperature.

Cooling Curve - explanation Temperature Time Heat removed from source Cooling most quickly around here Cooling is slowing down as it approaches room temperature Substance has reached room temperature Room temperature

Lesson 1: Cooling down Heat is a form of ENERGY Heat always moves from a hot place to a cooler place. A cup of hot coffee will cool down to room temperature. When an object is much hotter than its surrounding it will cool down faster Houses lose more heat in the winter. A large cup will cool down more slowly than a small one. Hot Heat Cold

Lesson 2: Conduction How does heat move through solids? What is a conductor of heat? What kind of substances are the best conductors? What is an insulator of heat? What kind of substances are the best insulators?

Starter Imagine you are in your bedroom Write down the sources of heat in your room.

HEAT CAN MOVE BY 3 METHODS CONDUCTION, CONVECTION AND RADIATION

Heat Transfer by Conduction Conduction occurs because the heat energy can pass from one particle to the next. It is most common in solids, where the particles are tightly packed together

What are Conductors and Insulators? A good conductor of heat lets the heat energy travel through it easily A poor conductor of heat (Insulator) does not let heat energy travel though it easily. Metals are very good conductors of heat Non metals (eg Glass, wood plastic) are poor conductors of heat They are insulators

Heat Transfer by Conduction Why is the saucepan made of metal but the handle is made of plastic? The pan needs to conduct heat to the cooking food but the handle must insulate to prevent heat passing to the hand.

Hot soup Plastic spoon or Metal spoon Cold hand Cold hand Insulator Metal spoon Conductor Hot soup

Experiment 1 :- Why does metal feel colder than wood, if they are both at the same temperature? Metal is a conductor, wood is an insulator. Metal conducts the heat away from your hands. Wood does not conduct the heat away from your hands as well as the metal, so the wood feels warmer than the metal.

Lesson 2 Experiment 2

Lesson 2 Experiment 3

Copy and Complete Substance Conductor or Insulator Used for Aluminium Steel Plastic Oven glove Wood

Conduction Video https://www.youtube.com/watch?v=wV7gzcKegdU

Lesson 2: Conduction Heat moves through some solids by conduction Substances that allow heat to move easily through them are called conductors. Metals are good conductors of heat. Substances that do not allow heat to move through them easily are called insulators. Air, plastics and wood are insulators. Heat energy is conducted from the hot end of an object to the cold end

Lesson 3 - Starter Which substances are good conductors? What do we call a substance that does not let heat travel through it? Give an 2 examples of these substances.

Lesson 3: Convection How does heat travel in gases and liquids? When parts of a gas are heated how, how does the gas move? When parts of a gas are cooled – how does it move? What is a convection current?

Water movement Cools at the surface Convection current Hot water rises Cooler water sinks

Convection in a Gas (air) Convection\Convection, chimney, hot air balloon.wmv

Heat Transfer by Convection Heat energy can also move through fluids (liquids & gases) by Convection. Liquids and gases are called fluids because their particles are free to move (flow). Hot fluids moves UP because it is less dense than cold fluids. When the hot fluids move, they are replaced with colder fluids.

Heat Transfer by Convection The movement of these particles is called a convection current. We usually cannot see the particles move but the following experiments allow us to see convection currents in a fluid easily.

Convection in a liquid (water)

Convection current in a liquid

Why is it windy at the seaside?

Where is the freezer compartment put in a fridge? Cold air sinks Where is the freezer compartment put in a fridge? Freezer compartment It is warmer at the bottom, so this warmer air rises and a convection current is set up. It is put at the top, because cool air sinks, so it cools the food on the way down.

YouTube: Demonstration of convection current in tubing. https://www

What can we learn from the video? Cold water falls Hot water rises Wisc-online animation: Convection BBCclip : Convection and Insulation Clip on Convection chimney, hot air balloon

Lesson 3 Convection Examples

Convection current Cold water falls Hot water rises Freezer

Convection in a room Where’s the warmest place? The radiator heats air which forms a current as shown in the picture: Warmer air rises; Cooler air falls. The ceiling is the warmest place!

Convection currents at the seaside Through the day the land becomes warmer than the sea At night the land becomes colder than the sea.

Lesson 3: Convection Convection happens in liquids and gases As a gas is heated, it warms, expands, and rises because it is less dense than the cooler surrounding gas. Likewise, when a liquid cools, it becomes more dense and falls. As the gas or liquid warms and rises, or cools and falls, it creates a convection current.

Lesson 4 - Starter Draw a diagram showing what happens in Convection Label the diagram

Lesson 4: Radiation What is the 3rd way heat can travel? What is heat radiation? What are some uses of heat radiation? What can heat radiation travel through?

Lesson 4: What is heat radiation Heat can travel by invisible rays. They travel in straight lines. Our skin can sense these rays. Use your palms to feel the heat of a far away hot object. These rays are called INFRA RED rays, because they are beyond red (so invisible). Wisc-online animation: radiation

Aluminium fire fighting suit Heat rays are reflected by shiny surfaces. Aluminium suits are used by firefighters to combat heat rays from fires. YouTube video: Aluminium firefighting suit

Thermal imaging Thermal images are made by special camera sensitive to infra red radiation (heat rays). The colours you see are not real. The scale shows the colour matched against temperature. YouTube: Man throwing hot and cold balloons

Heat radiation in cooking Infra red radiation cooks our food: YouTube video: Char-Broil TRUinfrared

All warm objects give off infra red radiation (IR). That includes warm objects in space. Infrared can travel through the vacuum of space. Astronomers use IR telescopes to look at stars, dust clouds, comets and asteroids. Now examine the following IR space photographs:

Constellation Orion Visible Light In visible light we can see the glow from stars and hot gas between the stars.

Constellation Orion Mid Infrared Light IRAS In infrared light we see the glow from cool stars and warm dust and gas. The warmest and dustiest places are also the brightest places in this image. They are locations of new star formation.

The Whole Sky Visible Light - Axel Mellinger This is an image of the entire sky seen in visible light. Visible Light - Axel Mellinger

The Whole Sky Near Infrared Light - 2MASS Survey This is the starlight of the Milky Way in near infrared light. Near Infrared Light - 2MASS Survey

The Whole Sky Mid/Far Infrared Light - IRAS Survey Here we see the glow of the disk of dust in the Milky Way (red) and scattered sunlight from the dust inside the plane of the Solar System (blue). Mid/Far Infrared Light - IRAS Survey

Lesson 4: Radiation Hot objects lose heat by giving off invisible heat rays. These are sometimes knows as infra red radiation. Infrared rays do not need particles to carry the energy. Radiation can travel through a vacuum or gas Heat travels through space from the sun to the earth by radiation

Lesson 5 - Starter How do hot objects give off heat? How is this form of heat travelling different from conduction and convection?

Lesson 5,6: Cooling Curves INVESTIGATION Black and Shiny Flasks Which cools the fastest – a black or silvered container? Start with same volume of hot water in each flask

Lesson 5/6 – Cooling Curves The black flask cools down faster than the silver flask. Black surfaces emit heat rays faster than silver Emit means to give out.

Lesson 7: Absorption of heat We can heat water in a container using a hot lamp. Which will heat fastest – the black or silvered container? Start with same volume of cold water in each flask

Absorption of heat The black flask heats up faster than the silver flask. Black surfaces absorb heat rays faster than silver Absorb means to take in

Lesson 8,9: Reducing heat loss How can we slow down the rate of heat loss from: our bodies? our homes? What materials and methods can we use?

Conduction This is an image showing heat loss from a house. The red parts shows where most of the heat is lost - through the windows and roof

Lesson 8,9: Reducing heat loss What do these things have in common? Polystyrene drinks cups, sleeping bags, birds fluffed-up feathers, double glazed windows, fleece jackets They are made with materials with trapped air in them – but why?

warm jackets have a lot of trapped air between its fibres Sleeping bags have fibres with air trapped between them Birds fluff up their feathers to trap air to keep warm Double glazed windows have air trapped in side to keep the house warm Materials with trapped air in them are good insulators What have these all got in common to reduce heat loss? warm jackets have a lot of trapped air between its fibres Polystyrene cups have lots of bubbles of air to keep drinks hot or cold

What are 5 ways to reduce heat loss in the home? For each of these, has conduction, convection or radiation been reduced? What are 5 ways to reduce heat loss in the home? 3 1 2 Draught Excluder Cavity Walls Convection Conduction Double Glazing Conduction Loft Insulation Conduction Carpets Conduction 4 5

Lesson 8,9: Reducing heat loss Materials with trapped air in them are good insulators For example Polystyrene cups keep drinks hot or cold Sleeping bags have fibres with air trapped between them Birds fluff up their feathers to keep warm Double glazed windows have air trapped inside to keep the house warm Fleece jackets have a lot of trapped air between its fibres

Lesson 8,9: Reducing heat loss from the home - Note

Reducing Heat loss from Buildings https://www.youtube.com/watch?v=qqivE90kF0g (good music but fast reading required) or https://www.youtube.com/watch?v=qUPb32O5-Ho Or https://www.youtube.com/watch?time_continue=1&v=50VB2p0osbE (an architect describes how her knowledge of physics helps her to design energy efficient buildings)