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	Podcast:		4. Chemistry and Physics
	Episode:		Conservation of Energy
	Category:		Science & Medicine
	Duration:		00:01:32
	Publish Date:		2011-07-13 19:49:17
	Description:		Transcript: One of the most important principles in physics is the law of conservation of energy. Energy can be neither created nor destroyed. In any closed physical system the total amount of energy is constant, although the energy may change forms multiple times. What do we mean by a closed system? We mean drawing an imaginary box around either an atom or an object or a planet such that all the processes occur within the box. Energy is conserved, but it can change forms. In an elliptical orbit, the kinetic energy changes constantly across the orbit, and the potential energy changes too. But the sum is constant. There are many examples of the transfer and change of one form of energy to another, but in every case, when the sums are done carefully, the total is conserved. In cases where it does not appear to be conserved the energy usually emerges in a subtle form. When a ball rolls and comes to a halt, or a pendulum swings and comes to a halt, it seems as if the energy of motion, the kinetic energy, has disappeared. But in each case the energy of motion has been replaced by thermal energy. For the rolling ball, the frictional energy increases the temperature of the surface due to the rubbing of atoms against each other, in the case of the pendulum, an increase in the microscopic motion of the air particles.
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