Review/summarize the ways that heat (thermal energy) moves:
Radiation can travel through empty space. We feel the radiation from the sun. Heat radiation is called Infra red. (Note that there are other kinds of radiation.)
Conduction and convection need particles. Conduction is the transfer of heat between things that are touching. Convection only happens in a liquid or gas, and is the movement of the particles themselves, carrying their heat energy with them.
Heat radiation demonstration
Best done in a circle, with an infra red heat lamp on a fixture that can be picked up by the teacher.
Tell the students that this lamp gives off some light, to show us where the heat is directed (which we can see) and heat (which we can't see).
Turn the lamp on and shine it briefly on each of the students' hands, so that they can feel the heat coming from the bulb.
Although we can't see heat radiation, we can still sense it - we can feel it.
The sun gives off radiation. Radiation can travel through space with no air.
(An old-style incandescent bulb also gives off a lot of heat, mostly by radiation. This waste of energy, when we want light, is why we have phased out incandescent bulbs.)
Look at infra red (IR) images together
Many materials give off heat radiation. IR cameras detect heat and convert the image to colours, so we can see where the most heat is.
Car: https://upload.wikimedia.org/wikipedia/commons/d/d6/IR_moving_car.jpg
Dog: https://animalwellnessmagazine.com/dogs-noses-detect-heat/
House: https://tedkinsman.photoshelter.com/image/I00000BT15x1yhIQ or https://www.loe.org/shows/segments.html?programID=12-P13-00046&segmentI…
Water rescue (scroll down): https://www.flir.com/discover/marine/first-respondents/maritime-public-…
Andromeda galaxy (4th image down): https://svs.gsfc.nasa.gov/30990
Heat radiation can pass through some materials and not others
Use heat sensitive paper to show heat. As it heats up the heat sensitive sheet turns from black to red, orange, yellow, green, blue, then black again. Demonstrate that the sheet turns colours when placed near the infra red heat lamp.
Does radiation pass through glass - do you get warm through a window? (It might be hard to remember, or separate what you remember from what you think should happen.) [Yes] Show with the heat sensitive sheet on the other side of the glass from the lamp.
Does radiation pass through plastic? Show with plexi sheet. [Yes]
Cardboard? [No]
Through water? Show it does pass through the plastic box, then add water to the box.
Just like visible light, infra red heat radiation can bounce off mirrors.
Hold the mirror so that infra red from the heat lamp reflects off the mirror and onto the heat sensitive sheet.
Free play radiation and conduction
Before the lesson: Space the the heat lamps around the classroom, minimizing wires to be tripped over (as students will be walking around the classroom a lot).
Before the lesson: Set up a shield so that the students cannot bring a heat sensitive sheet closer than 20cm to the lamp.
Hand heat sensitive sheets to students, and allow them to explore them for a while.
Discuss how heat moves from your hand to the sheet, to make it turn colours. Your hand and the sheet are touching - the heat moves between them by conduction.
Air is also touching the sheet and conducts heat away from it - there are molecules in the air that bounce into the sheet and take some of its energy and cool it down again.
Show students how to charge their sheet with the radiation from the heat lamp. Include a shield around the lamp, so students don't hold them too close and destroy them.
Then quickly touch it to materials in the classroom, to see how the heat leaves the sheet by conduction. Make sure the coloured side of the sheet is up, so you can see it change.
Allow students to explore.
After the radiation from the heat lamp heated the sheet up, which materials in the classroom conducted the heat away quickly, and which ones slowly? What patterns did you make on your heat sensitive sheets, when different parts of an object took heat away at different rates?
