Why do thunderbolts zigzag?

Lightning bolts strike the ground at right angles and they also leave the clouds at right angle because both are conductors (in that context). If the cloud base is not quite horizontal, the lightning bolt will not be straight down. Between the base of the cloud and the ground, lightning then follows a path where there are more impurities in the air. These impurities make it easier to create the ionized track that lightning likes to follow. As you might suspect, the impurities are not organized in straight vertical lines. This is why lightning follows these jagged paths.

For a lot more on lightning, see one of my favorites websites, How Stuff Works. 

To see John Travolta getting zapped, try this simulation (it's related). 

Why is it easier to float in salt water?

The short answer is "because salt water is denser than fresh water". That begs the question "so how does that help floating?"

To answer that question, we need to talk about Archimede's Principle. Archimede's Principle determines the strength of buoyancy. When you float in water, there are two main forces at work: gravity pulling you downward and buoyancy, holding you up so you don't sink. To be able to float, the buoyancy has to counteract the gravity. And in salt water, buoyancy is stronger.

Archimede's principle states that the strength of buoyancy is equal to the weight of the water you displaced by being in it. Consider a boat floating on water (forgive my art):

The boat has displaced a certain amount of water. The weight of that volume of water is equal to the buoyancy force that allows the boat to float. The more water the boat displaces, the higher the buoyancy force, because a larger volume of water weighs more. The boat will sink until there is enough of it under water to increase the buoyancy to a level where it can support the boat against gravity.

This, by the way is why boats need large empty spaces in order to be able to float. You want the boat to be able to displace a lot of water, while not being too heavy. Otherwise, even a large buoyancy becomes insufficient to counteract the downward pull of gravity.

Back to our question. How does the higher density of salt water help with the whole floating deal? In Archimede's Principle, what sets the strength of the buoyancy is the weight of the displaced water. Weight can be increased in two ways: 1) having a bigger volume, as discussed above, or 2) being denser. If the water is dense, then a given volume of it will be heavier and therefore, the buoyancy force will be larger. This is why it is easier to float in salt water than in fresh water.

Quiz: Is it easier to float in oil or in water?

Dad, I'm hungry! Why is the spaghetti taking so long to cook?

Growing up in Switzerland, pasta came with a special set of instructions on the box for cooking at higher elevation.

Pasta is cooked by immersing it in boiling water for some amount of time. At sea level, the boiling point of water is 100 degrees Celsius. At higher elevations, the boiling point is a few degrees lower. With decreasing atmospheric pressure, it is easier for the water to evaporate and it requires less energy (lower heat).

At 1000 meters above sea level, where a good number of Swiss towns are found, the boiling point is down to 96 degrees Celsius. At 2000 meters, were the lower ski resorts are, the boiling point is 93 degrees. And at 3000 meters, were the top of the slopes and mountain cabins are found, the boiling point is down to 90 degrees.

If you are hiking and you are attempting to cook pasta, instead of immersing it in water that is at 100 degrees Celsius, you are immersing it in water that is 10 degrees cooler. You will have to compensate by allowing the pasta to cook for longer.