Week 18 (Dec. 9 - 13)
Reading: Chap 15, fluids
Topics: Archimedes' principle; Hydrostatic pressure; Pascal's principle; Bernoulli's law; Sound
No quiz this week
Week 18 Homework Problems:
Hydraulics: A fluid-filled syringe has a plunger with a diameter of 1 cm. The needle has a diameter of 1 mm. The plunger is depressed at a rate of 1 cm per second. Hydraulics lab: This week, we will be building and analyzing a hydraulic jack system. Before getting started, you should take a few photographs of your assembled system. Then completely disassemble it, take another photograph showing the components, and then reassemble it. These photos should go into your lab notebook. Next, make a careful schematic drawing of your apparatus in which you label and explain how it is assembled. Be sure to include details about the make and model of the system. Do some experiments: first with air and then with water filling your system. When you use water, you will need to first bleed all of the air out of your system. Which works better: the air-filled jack or the water-filled jack? Why? Now do some careful measurements: diameter of pistons, length of stroke, etc. What is the mechanical advantage provided by your system? How did you figure this out? Does it behave as you expected? What, if anything, surprised you about your system? What could be done better? All of this should be recored, as always, in your laboratory notebook.
Some fascinating resources:
No quiz this week
Week 18 Homework Problems:
- Ice cube: A large ice cube, whose density is 0.917 g/cc, is placed in a glass. Water is then poured into the glass until the glass is full to the rim.
- First, what fraction of the ice cube is submerged? (Solution: 91.7 percent)
- When the ice melts, will the water level overflow the glass, will it fall below the rim, or will it remain the same? Explain your answer. (Solution: it would remain at the same level. Suppose the ice cube had a volume of 1 cc. 0.917 cc was below water. When it melts, the new volume will be 0.917 cc, since its density increased by just this much.)
- With what speed will the fluid squirt from the tip of the needle? (Since the cross-sectional area of the needle is 1/100 that of the plunger, the speed will be 100 times as great. So the fluid squirts out at 100 cm/second.)
- If the end of the needle is capped, and a force of 1 pound is applied to the plunger, what force will be applied to the end cap? Explain your answer. (By pascal's principle, the force will be 1/100 of a pound)
Some fascinating resources:
- The loudest sound in recent history occurred when Krakatoa erupted on August 27, 1883. Check out this article from Nautilus magazine: The sound so loud that it circled the earth four times. For a more technical report, here is VerBeeks' 1884 paper in Nature magazine detailing the Krakatoa eruption. VerBeek, R. The Krakatoa Eruption. Nature 30, 10–15 (1884).
- This video documentary of the December 2019 volcanic eruption on White Island has disturbing accounts from survivors who were trapped on the island.
- The pressure wave created by the explosion of a volcano of Papua New Guinea was documented in this video.
- On a different note, Wikipedia has a nice article on the famous Tunguska event of 1908, when a meteor struck in central Russia.
- And of course, there is the eruption of Mount St. Helens on May 18, 1980.