Teaching Physics with the Physics Suite Edward F. Redish

The 3 vase puzzle*

Water is poured to the same level in each of the three vessels shown. Each vessel has the same base area. Since the water is to the same depth in each vessel, each will have the same pressure at the bottom. Since the area and pressure is the same, each liquid should exert the same force on the base of the vessel. Yet, if the vessels are weighed, three different values are obtained. (The one in the center clearly holds less liquid than the one at the left, so it must weigh less.) How can you justify this apparent contradiction?

* From A. Arons, A Guide to Introductory Physics Teaching (John Wiley & Sons, Inc. 1990).

Note to the instructor: This problem is too challenging for many introductory physics students. For it to be interesting, the puzzle solver must have reached a stage of development where they cross-link ideas and seek coherence. Many introductory students have not reached this point. It might keep your colleagues puzzled for a while, however!

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