Homework:

1. Floating iceberg (Ex. 3.1),
2. The effect of buoyancy on a falling body: A pure indium ball having a diameter d = 1 cm is suspended from a tiny thread in a vacuum chamber. (a) What is the tension in the string? Hint: look up the density of indium (a soft metal). (b) If the ball is suspended in a vat of liquid gallium (instead of a vacuum), what is the tension in the string? Hint: look up the density of gallium. (c) If the thread is now snipped, what is the acceleration of the indium ball as it falls through the liquid gallium? Ignore drag (but not buoyancy) for now.

3. Falling gold balls (Ex. 3.2),
4. Sinking ball of wax (Ex. 3.3),

Lab: Archimedes' principle (Ex. 3.4). In this lab, we will attempt to verify Archimedes' principle by measuring the buoyant force exerted on submerged metal cylinders. In particular, we will suspend each of five (different) metal cylinders from beneath a Harvard trip balance and measure the weight (or perhaps the mass, in grams) of each. We will then measure the weight of each when it is suspended, fully submerged, in a graduated cylinder full of water. From these measurements, and the measurement of the volume of water displaced, we should be able to verify if Archimedes principle is correct. (How can we do this?)

In the course of our experiments, we will also try to determine the density, and hence the composition, of each of our five cylinders. You will probably need to use a bit of detective work (and a periodic table) to figure out each's composition.

Finally, using archimedes' principle, attempt to measure the density of ethanol by measuring the buoyant force on a metal cylinder suspended in a graduated cylinder full of ethanol. How do your results compare to the accepted value of the density of ethanol? Be sure to clearly cite the (respectable) source of the accepted value to which you are comparing your experimental results.

Chapter 2 (2 videos): In the following two videos, I discuss Galileo's attempt to measure how much nature "abhors a vacuum." He does this by measuring the force it takes to suspend a column of water in a cylindrical tube. You should watch these with the textbook in hand so you see how they relate to the text.





Chapter 2 (2 additional videos for PHY 201 folks): In the next two videos, Galileo wrestles with the novel concept of "atomism." In particular, he considers how matter might be comprised of innumerable infinitesimal pieces. Notice here that Galileo is dealing with topics that are related to calculus 50 years before Newton and Leibniz publish their famous work on calculus. In doing so, Galileo recalls the famous "rolling polygon" that was considered by Aristotle in the 4th century BC in his book Mechanics.





Chapter 2 (one more optional video): You can skip this last video if you want. Here is a brief summary. Galileo's character Simplicio believes that inanimate objects (like rocks) can act for purposes (or "ends"). Galileo's character Salviati, on the other hand, believes that inanimate objects -cannot- act for purposes (or "ends").



Here, Simplicio and Salviati are presenting the famous conflict between ancient/medieval science (the via antiqua) and early modern science (the via moderna). According to ancient/medieval science, nature has final causes (things act for a goal or purpose); according to early modern science, nature does not have final causes (things do -not- act for a goal or purpose).


Chapter 3 (8 videos): These videos deal with Archimedes' principle and the effect of buoyancy on falling bodies. You should watch all of these.