Unit Two: Energy Previously you have studied transformation of energy, for example in the electric bulb the electric energy is changed into light, also in the electric iron the electric energy is changed into heat energy and so on. Activity

1 (Conservation of mechanical energy)

Push with your hand gently a simple pendulum then leave it. • Record your observations about the pendulum motion. ……………..............…………. Repeat the procedure with two pendulum shown in the figure: • Record your observations ……….....…………. On displacing the pendulum, a work is done, this work is stored in form of potential energy. When it is left the potential energy is converted gradually into kinetic energy till it reaches a maximum speed where all of its energy is converted into kinetic one. This is repeated while the pendulum keeps its mechanical energy. ‫ب‬::‫ﺗﺪرﻳـــ‬ Exercise

1

How much alike are the motions of the children swing and the pendulum? • What do you observe? ................................... • Conclusion: ........................................................... In both the swing and the pendulum the potential and kinetic energies are interchanged without ending, the sum of the two energies at any moment is constant.

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