Over the break, I took a 5 day cruise into the Gulf of Mexico. Although there wasn't any internet connection for me to have Mr. Fullerton's videos grace my presence (I know what I'm going to be doing all day today), I was still thinking about physics the entire cruise. One particular event that made me use my physics knowledge took place when we were walking down the pier in Progreso, Mexico. Another Carnival cruise ship was leaving the port as we were about to get on our ship. The boat backed away from the dock and once it was out in the middle of the harbor, it began to turn in place. One thing that many don't know about large ships is the fact that they have large thrusters that exert a force perpendicular to the side of the boat, making lateral movements such as docking maneuvers much easier and safer. Another cool use for the thrusters is turning the ship in tight areas. There are 2 pairs of these thrusters, each pair on opposite ends of the boat and each thruster of the pair facing opposite directions. By using the thrusters on opposite sides and ends (two thrusters that are "diagonal" to each other), the captain can turn the ship on an axis to, in this case, point the ship in the direction of the opening of the harbor. On this particular day, there was a very strong wind blowing in from the ocean and while the boat was turning, there was no force vector produced by the thrusters that pushed the ship away from shore, so the wind was allowed to accelerate the ship back towards the pier. After the turn was complete, the ship was traveling with a small velocity backwards. Despite being a small velocity, the fact that a average cruise ship can weigh 60,000 tons automatically means any velocity will translate into an insane amount of momentum. This huge momentum was put on display as the main engines were fired up because even though the black smoke was pouring out of the smokestack, the boat continued to travel backwards for a few long seconds before finally the force of the engines met, and eventually overcame the momentum caused by the wind.
This application of a relatively simple concept is shown to have vital importance because without a sound knowledge of the relationships of the forces around him, the captain could have easily put the 3,000+ passenger's lives in extreme danger. It is really cool to think about the giant forces one must harness in order to make a cruise a success.