How does a thermal form?
NARRATION: Almost all our planet鈥檚 heat is provided by the sun. If you鈥檙e looking to unlock the secrets of the weather, the heat coming from up there is not as important as when it鈥檚 coming from down there, from the ground. I know it sounds unlikely but it鈥檚 all to do with the fact that the sun heats the Earth unevenly. Sand gets hotter than water. Tarmac gets hotter than sand. Concrete gets hotter than grass. And these differences produce pockets of warm rising air called thermals, which drive winds and createclouds.
But how can you see that effect for yourself? Well, with a quarry, five vehicles鈥 worth of kit, and two specially built metal tables. These tables are going to be our hot ground. Because they鈥檙e dark in colour they should soak up lots of heat from the hot sun. And to make sure they get hot enough, we鈥檙e going to give the sun a little help.
TO CAMERA: To be perfectly clear, my ambition here is not to actually make weather with this. I鈥檓 not hoping for a little square cloud overhead. The theory鈥檚 right, it鈥檚 just the scale is a bit small. What I will be doing, is creating that rising column of air - that thermal - which is part of the weather, and it is something I will be able to show you once I鈥檝e got it established.
NARRATION: So, let鈥檚 do all that, fire up the gas, and get me up above the tables so you can see the effects of our home-made thermal for yourself. Now, normally a paper helicopter would just spin slowly to the floor. But it doesn鈥檛. It hovers.
TO CAMERA: Fly! Oh, there you go, there you go, there you go! You can see how we鈥檝e created a thermal down there and the helicopters that catch it are flying in that column of rising air.
NARRATION: The updraft is enough to hold the helicopters in place. Just as they do naturally with clouds, raindrops and hailstones. But as the heat coming off the metal table increases the helicopters begin to climb鈥
TO CAMERA: Oh, yeah!
NARRATION: Until they鈥檙e disappearing out of sight, just like a real thermal. They can stretch up more than 1,500 metres - high enough to influence our weather.
Richard Hammond demonstrates how thermals are formed through heat from the sun.
Our planet鈥檚 heat is provided by the sun, but our weather is often driven by heat radiated from the Earth鈥檚 surface. As the sun heats different surfaces and areas of the globe unevenly, weather results.
These differences create thermals which create clouds and pressure differences, leading to wind. An outdoor experiment in a quarry demonstrates how thermals are formed. Paper helicopters are used to show the rising air.
Teacher Notes
This short film provides useful background for KS3 / KS4 students studying how clouds form. A KS3 class could use their sense of touch (or surface thermometer) to explore the temperature difference between different surfaces around a school building.
Curriculum Notes
This topic appears in geography and physics at KS3 and KS4 in England, Wales and Northern Ireland and National 5 in Scotland. At GCSE it appears in AQA, OCR A, EDEXCEL, EDUQAS, WJEC and CCEA, in SQA at National 5.
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