Gym class means that at one point, depending on who your teacher is and what units they're teaching, you're probably going to have to climb the rock wall located in the field house. You look at it and it doesn't look too bad, telling yourself that you can reach the top and it won't be a big deal. But first, in order to get to the field house, there's going to be some Physics involved. Depending on your velocity, that will vary how long it takes you to get to the field house: the faster you walk, the less time you'll take to get there, and that means the more time you'll get during class to climb.
The physics involved with rock climbing is, you're going to have some tension pulling on you, for example, there's a rope with 2 ends, one which is attached to this belt that you wear, the other attached to another person which will have other people backing them up in order to support your weight as you make it up the wall. It's a pulley system that's used, and as you go up the wall, the people on the other end will be taking steps back. When you're done, you let go of all the rocks, and gravity wants to come into play, and if you weren't connected to anything, you'd fall right onto the ground probably breaking a lot of things: including yourself. But since there are other people attached to the other end of the rope, they're there to bring you down slowly from the wall, and your velocity will depend on how slow or fast they walk in.
Rock wall climbing is fun if you're not afraid of heights, but remember to not look down if you make it all the way to the top of the wall.