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Imagine you have four "see-through" boxes, all the same size, and you fill each of them up with a different material.

Animated GIF of four boxes, one each filling with air, water, oil, and helium

Try to guess which material has the least mass, which has the most, and where the other two fit in between. (Mass is closely related to weight. Here on earth, for all practical purposes, it's the same thing.) Test your prediction by placing the materials two at a time on the balance below, and when you're ready to pick the one with the least mass, click on the box of your choice above.

Place on the balance...

air & water air & oil air & helium
water & oil water & helium helium & oil

Select the material with the least mass: Air | Water | Oil | Helium

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