"This session, we discussed two extremely large topics: energy and rotation.
We began with an explanation about energy. We listed out the types of energy including kinetic energy, potential energy, and elastic potential energy. We wrote out equations for each of them, and made flashcards for them. We said that energy is always conserved, so that the initial total amount of energy you have is equal to the final amount of energy you have. We then wrote down a long equation relating the initial and final amounts of potential, kinetic, and elastic potential energy of a system. We then moved onto the definition of work.
We then moved on to how you use energy to do a problem. We did a problem in which a box was being pushed by a force and we analyzed it via our method for forces, and then using energy. I stated that either way we would get the right answer, but that most commonly, it is easier to do questions with an approach of analyzing the energy states at different points in the system.
We did a complicated problem involving children and sleds and hills that was made a lot easier by using energy. We also did a problem where you can tell how quickly a pendulum is swinging at the bottom of its swing using energy.
We then moved onto the topic of rotation. We said that with rotation the acceleration is always pointing towards the center of rotation, and because the direction is always changing even though tangential velocity may be constant, it does not mean that the centripetal acceleration is zero. We talked more about the tangential velocity and that is always perpendicular to the radius from the object to the center of rotation.
We reviewed our seven step process again and said that if you determine that if you have a rotation problem you set you sum of the forces equal to mass times the centripetal acceleration, instead of mass times the linear acceleration. We stated that otherwise our method is exactly the same. We did a couple of problems together including one problem about a whistle being swung around a string. I again assigned the student homework problems, this time which were a bit more difficult: one energy problem, one rotation problem, and then a difficult rotation problem.
We made sure that we had created all of the necessary flashcards for the equations learned in this session and ended it there.
A fine class."