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Select the word from the list that best fits the definition classification of most stars on the h-r diagram

The focal length of a relaxed human eye is approximately 1.7 cm. when we focus our eyes on a close up object, we can change the refractive power of the eye by about 16 diopters. (a) does the refractive power of our eyes increase or decrease by 16 diopters when we focus closely? explain. (b) calculate the focal length of the eye when we focus closely.

Why is the energy that results from a roller coaster's position at the top of a hill referred to as potential energy?