# 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:

No quiz this week

Week 18 Homework Problems:

- I
**ce 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.)

**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.

- 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)

**Buoyancy problem:**TBD

Some fascinating resources:

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.