Adding a brief study of fluids to this course is new. We'll start with a simple demo. Place a beaker of water on an electronic scale.
Now, answer this: if I place my finger in the water, careful not to touch the sides or bottom, what will happen to the reading on the scale?
A) Nothing. It will stay the same.
B) It will go down.
C) It will go up.
D) Truth is relative. Science is a social construct. There is no correct answer, and yet all answers are correct. Because Reasons.
Feel free to leave an answer. You must show work to receive full credit.
If you are supporting the whole weight of your finger (and only your finger) than it adds nothing to the weight of the water. If you are letting your finger float a little bit, even unconsciously, then you're adding that much weight. But if some of the water clings or adheres to your finger, above or below the waterline, and if you support the weight of that water along with your finger, then the weight of the beaker and its water will drop.
ReplyDeleteSo the answer is relative (to what your finger does in the water.) There is no single correct answers, all answers might be correct -- depending on the conditions. Define the conditions sufficiently, though, and the truth you get is really true. Because Reason.
Now that the demo is over I can reveal that the correct answer is C. (The answer is always C). There are a number of ways of looking at it, the simplest is that dipping your finger raises the water level. The bottom of beaker doesn't "see" your finger, it just responds to the higher water level--the same as if you simply added an amount of water equal to the volume of the submerged part of your finger. So the scale reading goes up. And the farther you dip your finger, the more it goes up. Eureka.
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