About 400 years ago, Leonardo da Vinci wanted to fly… so he studied the only flying things around at that time: birds and insects. Then he did what any normal kid would do—he drew pictures of flying machines!
Centuries later, a toy company found his drawing for an ornithopter, a machine that flew by flapping its wings (unlike an airplane, which has non-moving wings). The problem (and secret to the toy’s popularity) was that with its wing-flapping design, the ornithopter could not be steered and was unpredictable: It zoomed, dipped, rolled, and looped through the sky. Sick bags, anyone?
Hot air balloons that took people into the air first lifted off the ground in the 1780s, shortly after Leonardo da Vinci’s plans for the ornithopter took flight. While limited seating and steering were still major problems to overcome, let’s get a feeling for what our scientific forefathers experienced as we make a balloon that can soar high into the morning sky.
Materials: A lightweight plastic garbage bag, duct or masking tape, a hand-held hair dryer. And a COLD morning.
Here’s what you do:
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i live in Saskatchewan Canada so we don’t have any problem getting it cold.
This experiment demonstrates how warmer air rises in cool air because it’s lighter (less mass (atoms) per unit volume) than cool air. In fact, each cubic foot of warm air can lift approx 7 grams, since the warm air from the hair dryer weighs 7 grams less per cubic foot than room temperature air (so make sure your bag and tape don’t weigh more than 20-30 grams, depending on the size of your bag!)
Can you explain the significance of air pressure in this experiment? We know that hot air rises, does that mean that cold air has a higher pressure and is pushing the hot air?
The main idea is that the greater the temperature difference, the more quickly your bag will float. If there’s no temperature difference, it will sink to the ground. With a little difference, then it will hover in front of you. So you can either decrease the outside air temperature by doing this on a cold morning or heat the inside air enough to work, but not so much that it melts the bag. Does that help?
How cold does the morning have to be? We live in Vegas, and since we are in way past cold mornings, I’m just wondering if I’ll have to wait to do this, or do I have to wake my kids up at sunrise? Or if we go into a room and blast the AC, how cold do I need to set the thermosat?
Oops -sorry about that. I fixed the link for you… everything works now. 🙂 Here’s a worksheet (included when you purchase the solar tube) that includes questions, project ideas, and explanations. Does that help?
Hi there, just wanted you to know that the link to the 60 foot solar tube isn’t working. I haven’t watched the video yet but I was wondering about the science behind this. Is it that the warm air pushes up or is it the cooler air pushes it? Just trying to figure what to say to the kids when they ask why that works. Thanks