Full of Energy

B and F Blocks began their study of work and energy today by nailing down the scientific use of the term "work," looking at how the direction of an applied force affects the amount of work it does on an object, examining situations involving positive and negative work and relating work to the kinetic energy change of a object. For F Block, the lab we conducted yesterday helped to highlight the ideas of work and energy. The ball's fluctuations in kinetic energy related to it's speed and represented the work done on it by the person throwing the ball and by gravity while the ball was in free fall. You did positive work on the ball tossing it upwards (sped up), gravity did negative work on the ball on the rise (slowed down) and positive work on the way down (sped up) and you did negative work on the ball when you caught it (brought it to a stop). Tomorrow, we'll add the potential energy piece to the mix.

C Block built on their study of work and kinetic energy by adding in two potential energies we class as mechanical energies - gravitational potential (PE_g) and elastic potential (PE_elastic). Both are readily available for active work, unlike chemical or heat, and are easily convertible to kinetic energy. Both are energies of position - position in earth's gravitational field and final position based on stretch or compression. Changes in position (lifting, dropping, stretching, compressing) represent work being done - these energies represent the stored work that you did. Release that energy and that equivalent of work can now be done by the object. On Wednesday, you'll do a lab that will look at potential energy and it's conversion to kinetic in a dynamic system. That lab will also bring in tomorrow's discussion about conservation of energy.

E Block conducted a lab that looked at energy conversions for a ball tossed in the air. You tracked the changes in kinetic and gravitational potential energy and clearly saw the inverse relationship between the two. The total energy, however, remained constant, demonstrating the conservation of mechanical energy in that low-friction system. That went down the tubes when you allowed the ball to bounce on the floor. Mechanical energy was not conserved as a goodly portion of it was converted to heat, internal energy and sound with each bounce. Total energy in a closed system is always conserved, but mechanical energy declines with time due interactions with other objects in the system. We'll go over the lab tomorrow and refer to it frequently in our discussions of work and energy in this chapter.