How to apply energy conservation

States of the system for a falling paper clipConservation of energy is usually applied between two different states of a system before and after a change. In the context of physics a state is a particular configuration of all the elements in the system that has a certain energy. The change rearranges one or more elements in the system, usually transforming or transferring some energy. If the system is closed, the total energy before the change is the same as the total energy after the change. The distribution of energy in the system before and after the change determines what changes are possible. Read the text aloud
Popular legend holds that Italian scientist Galileo Galilei dropped two balls, one ten times more massive than the other, from the top of the Leaning Tower of Pisa to demonstrate that, in the absence of air resistance, the acceleration of gravity is independent of the mass of the object. Historians dispute that Galileo actually performed this experiment, since only Galileo’s secretary claimed in writing that he had done so. Even if Galileo never did the experiment, we can use conservation of energy and a few paper clips to test Galileo’s hypothesis. Read the text aloud Leaning Tower of Pisa
Which falls faster, 1 paper clip or a group of 10 paper clips together? Read the text aloud
Change of the state for a single paper clip and a group of paper clips
Energy before the change equals the energy after the changeBefore the change, neither mass is moving, so there is only potential energy. After the change, the height is zero, so there is only kinetic energy. For each system we set the energy before the change equal to the energy after the change and solve the resulting equations for the speed v. The result is the same for both! In the absence of friction, the speed depends only on the change in height h. Galileo was correct in his conclusion. Read the text aloud Show Then why does a feather fall slower than a rock?
If you drop a bowling ball and a tennis ball from the same height, which one will hit the ground first? Show

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