Watching the Rise and Fall

C Block worked on a lab that focused on energy transformations and energy conservation for an oscillating spring. The spring constant was experimentally determined and used for the calculation of elastic potential energy. The object's mass was a known value and the motion detector provided displacement and velocity information for the final energy determinations. The graphs of kinetic energy and elastic potential energy showed nicely the inverse relationship between the two and adding a plot of total energy demonstrated its conservation throughout the oscillations. No matter how often the energy is transformed, the total remains the same. Adding an index card to the bottom of the oscillating mass increased air resistance and the conservation of mechanical energy suffered due to energy transformation to non-mechanical forms. We'll discuss the lab in class tomorrow, go over the conservation of energy homework problems, then launch into a discussion of power.

B and E Blocks finished up our basic mechanical energy forms by adding gravitational potential and elastic potential to the list. Both are energies of position and both represent stored energy. Both are related to the amount of work done on or by the object and both are readily accessible by objects for work. When working problems, make sure to double-check the reference point for measuring height for gravitational potential energy. It isn't always the ground...

F Block took time to review kinetic and potential energies before looking at conservation of energy. Conservation of total energy is a fundamental law of the universe, but conservation of mechanical energy is valid only in low-friction systems. Transformation of mechanical energy to non-mechanical forms or forms useless for motion will reduce the overall mechanical energy the system has available over time. We are going to assume for your homework problems that mechanical energy is well conserved so that ME_i = ME_f. It is up to you, though, to use that relationship to come up with a proper equation to work with this concept in specific situations. We'll go over these problems tomorrow and then take a look at power.