Question 2: This container sits on a table and is filled with water as shown. It

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Question 2: This container sits on a table and is filled with water as shown. It is open to the air at the top left. You often hear (including in our textbook that pressure is "the weight of the water above," which is a good place to start but can sometimes get you in trouble. 1 2 Every square you see here represents an infinitely small cube of water (so small that pressure doesn't vary from the top to the bottom of it). Your question is: is the pressure at points A and B (orange squares) different and if so, which is higher? For your answer, write an argument that is not based on the statement that the pressure is the weight of the water above, which is only true when there is no wall above you (as in case A). Instead, base your argument on these facts: 1) The pressure at any point in a fluid at rest is isotropic, which means that it exerts the same force in every direction (this term is common in physics but not used by our text); 2) Each fluid element is at rest so the sum of forces on it is zero; 3) Newton's 3rd law. See Figure 13-1 of Giancoli's book (page 341, 4th ed.) and the accompanying text read it if you haven't yet. The term "isotropic" means the same in all directions, and it is commonly used in physics, although not in our textbook. The yellow fluid elements (cubes labeled 1 and 2 are there to help you make your argument, but there are other ways to make it that don't require you to look at those two particular bits of fluid, too.

Explanation / Answer

On the same horizontal plane the pressure is same. Points A and B is on same horizontal line so the pressure is same at both points.

Take another argument : Lets assume that pressure at A is less than that of B. If this were true than water should flow from the region of high pressure to low pressure. But water is at rest which indicates that all forces are balanced and pressure is same at A and B.

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