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The Laws of Thermodynamics

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  • 0:03 Laws in Everyday Llife
  • 0:40 First Law of Thermodynamics
  • 3:21 Second Law of Thermodynamics
  • 4:44 Energy in a Closed System
  • 7:12 Lesson Summary
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Lesson Transcript
Instructor: Greg Chin
Learn about the first and second laws of thermodynamics. Find out how energy is generated, how it converts from one form to another, and what happens to energy in a closed system.

Laws in Everyday Life

All kinds of laws govern our everyday life. Traffic laws tell that you have to stop at stop signs. Government laws demand that you give a portion of your salary to state and the federal government. Even scientific laws apply to everyday life. For instance, the law of gravity predicts a pretty poor outcome for anyone attempting to fly. Another set of scientific law that affects our everyday life are the laws of thermodynamics. So, let's look at a set of examples to see how the laws of thermodynamics apply to everyday life.

First Law of Thermodynamics

The first law of thermodynamics states that energy can't be created or destroyed, but you can convert it from one form to another. This is also sometimes referred to as the law of conservation of energy. So, how does this apply to our everyday life? Well, let's consider the computer that you're using right now. It's powered by energy, but where did that energy come from? The first law of thermodynamics tells us that this energy couldn't have appeared from out of thin air, so it came from somewhere.

Let's start tracing that energy back. We know that our computer is powered by electricity, but where did that electricity come from? Well, it came from a power plant. Now, that power plant could've produced that electricity in any number of ways. Let's consider an example where the power plant is a hydroelectric power plant. So, the hydroelectric power plant is going to be associated with a dam, and that dam is holding back a river. A river has kinetic energy associated with it, meaning that the river is flowing. It's moving and has kinetic energy, right? The dam is converting that kinetic energy into potential energy, meaning that I've stopped the river from flowing. That river wants to continue to flow and release that potential energy that is being stored up by the dam.

How energy can transform into electricity
Energy Conversion

How a hydroelectric power plant works is we can we release some of this water into our hydroelectric plant, and I can use the water to spin a turbine. In spinning the turbine, I can power the generator, which is going to create electricity. This electricity can be piped all the way in wires from the power plant to your home so that when you plug your power cord into the electrical socket, the electricity will flow, and your computer will be able to work.

Consider what happened here - we already had a certain amount of energy that was associated with the water in the river as kinetic energy. What happened then was that kinetic energy was transformed into potential energy by the dam. That dam then took that potential energy and turned it into electricity, which was then able to travel to your home and power your computer.

Second Law of Thermodynamics

Now, the second law of thermodynamics states that not all energy can be used. Let's consider another example. Say that you have a stalled car, and we are trying to push that car down the street. When I push the car, the car moves a certain distance and then stops; it doesn't just keep rolling on indefinitely.

This is the second law of thermodynamics in action: not all the energy can be used. If all the energy I applied to the car could've been used, the car could've continued to use that kinetic energy until I stopped it. However, we know that energy is slowly lost over time and that causes the car to stop. When I pushed the car, I infused that car with kinetic energy. Those rubber tires started to move and continued to move down the street. However, the rubber of the tire is scraping against the pavement. As it scrapes against the pavement, it's going to produce heat due to the friction. Heat is another form of energy, but heat isn't kinetic energy.

Energy in a Closed System

What's happening is, as the tires move across the pavement, I'm slowly removing some of the kinetic energy and turning it into heat. I'm turning it into an unusable form of energy as far as I'm concerned in terms of moving the car. If I graphed the total amount of energy for this car over time, I could describe the different types of energy that exist in this system at any given point.

Graph showing the total amount of energy over time
Closed System Energy Graph

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