| Steve and Stacy are planning to ride a hot air balloon this weekend with their kids. Suddenly, a question pop out of Steve's mind. |
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 | Do you know why hot air balloon rise? | |
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| Yes. As you know, a hot air balloon rises because the air inside the balloon is hotter than the air outside the balloon. This difference in density allows the balloon to float upwards. | |
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| Oh I see. I think it is somehow related in fluid mechanics ideas. the forces acting on the balloon, we realize a buoyancy force is pushing upwards on the balloon, while the drag force and the weight of the balloon and the air it contains acts downwards | |
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| Exactly. This change in density also affects the magnitude of the drag and buoyant forces, which in turn affects the velocity at which the balloon rises | |
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| I think our children would be more excited to know about this knowledge. | |
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| That's true. Come on and let's go back to work. | |
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