Methods of Heat Transfer 28/11/2018 Methods of Heat Transfer By the end of the lesson you should be able to: Explain how tinned peas warm up in a pan Why robins don’t freeze in winter Key words: (Can you think what they might mean?) Conduction Convection Radiation Insulation This lesson needs a table: What is c,c,r and how it happens, does it need particles etc -Write down today’s title, lesson objectives, key words and the date. Draw the picture -> -> -> -> -> -> -Underline all of your work
How do our peas cook? How does heat energy travel from the hob to the peas?
Conduction Thermal Energy Conduction is the transfer of heat energy from a hotter to a colder region Particles vibrate, transferring energy to their neighbours, which in turn vibrate too. The thermal energy moves, but the particles stay put. Heat energy transfers best in solids – why is this true? Poor conductors are also called insulators Need the different rods with wax on and different metals with temp strips on. Or lots of different materials – time how long before end gets hot How do different solids and metals compare? => Demo time……
Poor Conduction In this experiment we saw that liquid water is a poor conductor of heat. The ice cube did not melt even though the water above it was boiling. Demo the Ice in water experiment Air is also a poor conductor of heat. This is how many types of house insulation and clothing keep us warm.
Convection How does a lava lamp work? 28/11/2018 Convection How does a lava lamp work? Use these words in your explanation: Density Rising/falling Cooler/hotter Expansion/contraction
Convection Gases and liquids When a liquid or gas is heated the hotter liquid/gas rises The cooler liquid/gas moves in to replace it This is a convection current Heat travels through gases and liquids mainly by convection When a liquid or gas is heated the hotter liquid/gas rises The cooler liquid/gas moves in to replace it This is a convection current
Words to use: expands, radiators, dense, heated, current, float Convection 28/11/2018 Convection is all about when a gas or liquid (“fluid”) moves and carries heat energy with it. When the fluid is heated it ____________. This means that it will become less __________ than the colder fluid around it. As a result, the warmer fluid will try to “_______” over the colder fluid, and this is why warm air rises. This is called a convection ___________ and is how heat reaches us from the ___________ in this room. Verbal DART – answers on whiteboards Words to use: expands, radiators, dense, heated, current, float
How is convection helping here?
Off and Onshore Breezes
Other examples of convection What about in central heating?
How does the sun’s heat energy reach us? Why are some houses painted white?
Radiation Everything gives off heat radiation. The hotter the object, the greater the energy of the radiation. It travels as a wave in a straight line and needs no particles to help it move, so can travel through the vacuum of space. White board activity vacuum particles greater radiation
Draw a diagram to show the ‘tin lid demonstration’ and then complete the sentences below: Investigating how different surfaces absorb heat energy: One tin lid was painted with ______ paint whilst the other was unpainted and had a ________ metal surface. Each tin lid was held at _______distance from a blue Bunsen flame. This means that each lid receives the _______amount of heat energy. The lids absorb heat energy radiated from the flame. This heat energy is transferred through the lid by ___________ and causes the wax to ____. The more rapidly the lid absorbs heat, the more rapidly the wax will melt.
How does a thermos flask work? Stopper This is your prep! Vacuum Glass Hot liquid Silvered Surfaces This can be set for prep Hot liquid Glass
How does the sun’s energy reach us? Conduction Radiation Radiation Convection Conduction Atmosphere – A gas Space – A vacuum Alien - solid
Electric Bar Heater – just radiation here?
Of course not!!! Convection Radiation Conduction Silvered surface
White Boards: What is the MAIN method of heat transfer Conduction Convection Radiation electric bar heater ☺ fan heater blowing hot air radiator saucepan on electric hob Quick Activity: Could replace 2 above on alien and just the heater. If the group is sensible, provide them with a woolly hat, fur hat, al foil hat and bubble wrap hat. Stand in 4 corners of the room and then vote with your feet. They need to sell according to WHY it keeps them warm. Else, make them look at this slide.
How is insulation working here? 28/11/2018 How is insulation working here? Pick a picture, draw it and write how insulation is working here. Feedback.
Conductors or insulators? School Jumper Table Water Air Plastic Metal If time
28/11/2018 Pick one to describe How best to insulate a house against heat loss by convection, radiation and conduction How do birds keep warm? How the sun’s heat energy reaches us? Why houses in Greece are often white? Why wearing white in summer is better than black? What are off and onshore breezes? How do hail stones are able to grow in size within a cloud? Why do large birds hover over motorways? Why do metals get hotter faster than plastic?
Check your learning Different surfaces absorb and radiate heat energy at different rates. Darker colours radiate and absorb heat energy more rapidly than lighter colours. Black surfaces radiate/absorb most rapidly. Matt surfaces radiate/absorb heat energy more rapidly than shiny surfaces.