Helium Balloon: Buoyancy & Slow Deflation

A side-view cross-section of a room with a helium balloon tethered to the floor. Release it and real Archimedes buoyancy — the weight of displaced air minus the weight of the balloon and its gas — lifts it toward the ceiling, while a simplified but genuinely Fickian diffusion model steadily drains its helium fraction through the latex, tracked live on a strip chart of height and lift force. Adjust balloon size, latex thickness, initial helium purity, ambient temperature and time compression, or drag paperclip weights onto the string to see exactly how much extra mass it takes to ground a balloon before it naturally settles on its own.