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	Podcast:		4. Chemistry and Physics
	Episode:		Energy
	Category:		Science & Medicine
	Duration:		00:01:10
	Publish Date:		2011-07-13 19:35:57
	Description:		Transcript: Scientists define energy as the ability to do work. You can also think of energy as something that can cause a change. This sounds vague. But scientists have defined energy in many careful ways, and it is a clearly quantifiable concept in physics. Next time you drive your car, consider the source of its energy. Millions of years ago sunlight was intercepted as it traveled through space and was used to grow plants on the ancient Earth. Those plants died, decayed, and were deposited into rocks where they turned into petroleum. Many millions of years later humans dug up the petroleum, purified it, and turned it into the fuel for your car. Your car extracts the chemical energy from that petroleum and turns it into the kinetic energy of motion. As you put your foot on the brake and bring your car to a halt, the kinetic energy is turned into the heat in the brake lining and in your engine, and it rises up into the air to eventually seep out into space and continue its journey onward.
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