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# Volume/mass?

why do you use three bags and not just one bag, do you have some math to go beyond the just do this video and instruction?

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why do you use three bags and not just one bag, do you have some math to go beyond the just do this video and instruction?

## Discussions

If you are going to get the kids involved the bigger the better but from experience size is limited by practicality

Thanks, I was too lazy to do the math when I read it, I was hoping that a simple analysis was done by the instructor.

In general is Instructables just to show cool demos or is the purpose to have the demos and projects and also include the underlying scientific principals in math / formula format so the student can explore varying the parameters? We could totally expand this with a free body diagram of the envelope (the bag and string) which has mass and then give the equations for the density of the air in the balloon and could even expand into the heat transfer to the bag (balloon) from the sun. Which could go from simple to very complex, but it may give the basic tools for an interested party to explore the parameter space and maybe expand the project beyond. More importantly, make the connection from the words here to physics and math and environmental sciences / engineering.

What is the level that is targeted here?

Are you asking that about Instructables in general or about this solar class in particular? I think for Instructables in general, the idea is to show people something cool you made in a way that they can reproduce. The level of scientific principals included in the instruction is entirely dependent on the individual author, and how much or how little they choose to include. I've certainly seen some examples that go very deep into science, then others that skip over the "why this works" completely.