Kids are full of curious questions, often asked repeatedly, and usually right when you’re trying to cook. One such question came from the 9-year-old child of a Reddit user, who wondered : "If helium is lighter than air, would a balloon with a vacuum in it, also float?" The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.

An excellent and enjoyable question. First, sorry 9-year-old, let's look at why helium balloons float. Buoyancy is an upwards force in a fluid (any flowing substance, including air) exerted on all bodies within it. The force comes from the pressure within the fluid being greater the further down the fluid you go. The pressure on the bottom of an object within the fluid is higher than at its top, causing the upwards force

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