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Mystery #3Tier 2-3air / forces / density

Why does a huge, heavy hot-air balloon rise into the sky?

A hot-air balloon is enormous and carries people, baskets and heavy gas burners. By rights it should thud to the ground. Instead it drifts upwards. With nothing holding it up and nothing pulling it, what lifts all that weight into the sky?

A large hot-air balloon in a checked pattern of black, red and gold floating high in a clear blue sky, with passengers visible in the wicker basket slung underneath
Photo: Alexey V. Kurochkin · CC BY-SA 4.0 · via Wikimedia Commons

Your guess

What do you reckon makes the balloon go up instead of falling down?

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