Does super cooled helium act in a viscous or non-viscous manner?

Below 2.17 K, liquid helium behaves very differently than normal fluids. It behaves as though it were made of two intermingled fluids: one that is normal in every way and the other that is completely without viscosity. Depending on what sort of experiment you do, you will see one or the other fluid. If you swirl the liquid helium with a stick, you will see the viscous fluid component swirling and splashing. If you pour the liquid helium through a filter made of tightly packed dust, you will see the non-viscous component rushing through. No normal fluid can travel through packed dust, because its viscosity slows its travel until it doesn't move at all. But the viscosity-free component of liquid helium can flow easily through any holes, no matter how small. It can flow through holes that even helium gas has trouble passing.

We discussed the fact that water seeks areas of lowest pressure. Is this the concept behind low pressure weather systems bringing precipitation and high pressure bringing clear, dry conditions?

Not really. Fluids do accelerate toward lower pressures, so a low pressure weather system does attract surface winds (the air near the surface of the earth accelerates toward regions of lower pressure). But the precipitation issues are generally related to temperature changes. Hot air can hold more moisture than cold air, so if a low pressure system attracts air and causes hot and cold airs to mix, the new air temperature and moisture may be incompatible. When that happens, the moisture emerges from the air as water droplets and it rains.

Why is viscosity important in motor oil for today's high revving engines?

If the oil in your car is has too little viscosity, it will easily flow out of the gaps between surfaces and will not lubricate them well. Those surfaces will experience sliding friction and wear. If the oil has too much viscosity, it will waste the engine's energy by opposing motion and turning work into thermal energy. Modern motor oils have carefully adjusted viscosities that balance the two problems. Since temperature affects viscosity (hot molasses has less viscosity than cold molasses), motor oils add chemicals that stabilize their viscosities over wide temperature ranges.

Why can't you pull the water up above a certain point without a pump?

When you draw water up through a pipe (or straw) by removing the air inside that pipe, you are allowing the atmospheric pressure around the water to push the water up the pipe. The water experiences a pressure imbalance between the pressure around it (atmospheric pressure) and the pressure in the pipe (less than atmospheric pressure), so it accelerates into the pipe. But as the water column inside the pipe grows taller, a new problem appears: gravity. The water's weight pushes downward and begins to oppose the pressure imbalance. At a certain height, the two effects balance and the water stops accelerating upward. When the water height reaches 10 m, atmospheric pressure can't overcome this weight problem, even if all the air has been removed from the pipe.

Why does a hose squirt further when you cover the hole with your thumb?

The water entering the hose has a certain amount of energy per liter. That energy can be in one of three forms: pressure potential energy, gravitational potential energy, or kinetic energy. If you let it flow freely through the hose, most of that energy will become kinetic energy and the water will move quickly through the hose. But it will encounter frictional effects as it slides past the walls of the hose (it viscosity participates here) and it will convert much of its kinetic energy into thermal energy by the time it leaves the hose. However, if you pinch off the flow with your thumb, the water won't be able to convert its energy into kinetic form as it enters the hose. Most of the energy will remain as pressure potential energy. The water will move slowly through the hose and it will experience relatively little energy loss to frictional effects. Most of the energy will remain by the time the water reaches your thumb. Then, as the water flows past your thumb to the outside air, its pressure will drop suddenly and its energy will become kinetic energy. The water will spray out at very high speed.

Does air create a friction force on water? (E.g. would a gutter be much quicker at having water flow through it, rather than a pipe?)

Air does exert frictional forces on water, but much less than a surface would. Thus a gutter would be a better water carrier than a pipe. It would have one less surface to slow the flow of water.

How does Jello work? How come it congeals when it is cooled?

Jello is composed of long, stick-like molecules. When you dissolve it in hot water, those molecules separate, but as the liquid cools, they begin to stick together like a giant heap of straws. The water flows slowly through these straws because of frictional effects. The result is a stiff material that is given its structure by the straw heap. If you leave the Jello long enough, the water will seep out and make puddles on the plate.

Why did the air-filled test tube sink when the bottle was squeezed? If you squeeze the bottle, wouldn't the air's density increase but the test tube's density stay the same? Shouldn't the test tube keep floating?

The test tube and air bubble are working as a team. The test tube is more dense than water and the air bubble is less dense. Together, they have an average density that is just less than that of water. But when you squeeze the bottle, you squish the air bubble so that its density increases. The average density of the test tube and air bubble increases so that it's more than the density of water. The test tube and air bubble sink together.

Why are water towers larger on top than on the bottom?

The goal of the water tower is to store water high in the air, where it has lots of gravitational potential energy. This stored energy can be converted to pressure potential energy or kinetic energy for delivery to homes. Since height is everything, building a cylindrical water tower is inefficient. Most of the water is then near the ground. By making the tower wider near the top, it puts most of its water high up.

I don't understand the tall sucking tube. Is this important? What are we supposed to know?

You should know that in a straw, it's atmospheric pressure that is pushing the water up to your mouth, not some magic suction that is attracting the water toward you. You should know that water's pressure increases with depth because of the need to support more and more weight overhead. And you should know that atmospheric pressure is only able to support a column of water that is about 10 m high. To lift water higher, you need extra pressure; usually provided by a pump.

What is the concept of vortex rings?

These rings (also called smoke rings) are moving portions of fluid that are moving relative to the surrounding fluid. They form a remarkably stable structure. The inner edge of the ring heads forward, while the outer edge head backward and the ring pulls itself through the air. Fluid dynamicists study these sorts of objects.