The hot air balloon is the oldest successful device capable of carrying humans in flight–the first successful manned flight was on November 21, 1783, in Paris by Jean-François Pilatre de Rozier and François Laurent d’Arlandes.
A hot air balloon is constructed out of an envelope (the bag that holds the hot air) that is capable of withstanding the heat from the air, beneath the envelope is a container of some type (called a gondola when it carries people in it) which contains the payload along with a source of heat that’s typically an open flame. The heated air that’s contained in the envelope makes it buoyant because it has a lower density than the air outside, which is much colder relative to the air inside. Now
| what we’ve got here is a very simple and easy to make hot air balloon that consists solely of some birthday candles, a bit of balsa wood, and a vegetable bag from the grocery store–I love that he says these things have been mistaken for and reported as UFO’s, that just makes me want to do |
it so much more 😀 , have a look and stay tuned afterward for some science:
The envelope doesn’t need to be sealed at the bottom like with gas (helium) balloons because the gas (in this case air) at the bottom of the envelope is at the same pressure as the surrounding atmosphere. When you
| raise the temperature of the air contained in the envelope, this makes it lighter than the surrounding atmosphere of air, thereby causing it to literally float, just like a boat in water: the balloon floats in the earth’s atmosphere near the ground because of the buoyant force exerted on it, which is the same force that |
causes buoyant objects, such as boats, to float in water and is described by Archimedes’ principle: “Any object, wholly or partly immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.” So therefore the amount of lift (which you could also call buoyancy, technically) produced by a hot air balloon is dependent mostly on the temperature difference between the air inside the envelope and the air (atmosphere) outside the envelope.
Additional Resources
Here’s a really cool set of instructions on how to make a hot air balloon with some tissue paper, it’s aimed at 6th graders and the balloons certainly end up a lot prettier than one made from a plastic bag 🙂