Science Buddies: "Ask an Expert"

Hi! I am making the solar updraft tower for my physics project according to your videos. However although the temperature reached 51℃ inside, the propeller still did't spin. I wonder the approximate temperature when the propeller starts spinning. And moreover, I made the propeller with A4 paper, is that because I didn't use the construction paper? And will the distance between the tower and the propeller matter? Thank you!





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The activity can be viewed at: Build a Solar Updraft Tower

Hi - there isn't a specific temperature at which the propeller will start spinning, it will depend on the individual setup. You will want to make sure that the propeller is low-friction and you can spin it easily by hand. If the propeller is hard to spin or comes to a stop almost right away when you spin it and let go, then there is probably too much friction for the rising warm air to make it spin. The type of paper should not be critical to getting it to work - minimizing friction is the most important. We haven't tested it with different distances between the tower and propeller, but you could try changing that to see if it has an effect. Hope that helps!