# The Laws of Thermodynamics

1. 0:40 First Law
2. 3:24 Second Law
3. 4:50 Energy in a Closed System
4. 7:14 Lesson Summary
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Need a good excuse for why your room is never clean? Try telling Mom that you're just following one of the laws of thermodynamics. Check out this lesson to learn more.

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.

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 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.

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.

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.

So, the total amount of energy is not going to change over time. We've established that in the first law of thermodynamics. However, the first law of thermodynamics did say that energy can be transformed into different forms. What happens in the real world is we're only ever measuring usable energy. In the case of the car, we are usually only measuring kinetic energy as the car moves. If we take into account the energy at time zero, then all this energy here is kinetic. As time moves on, and I measure the kinetic energy of the car, that is going to decrease over time until it gets to the point where it's zero and the car stops moving. If at the same time, I was to measure the unusable energy that is being produced over time - that is the heat that is being lost to friction - that is increasing over time. If I were to measure the car at any point in time over the distance it travels, I'd see that the kinetic energy is decreasing and the heat that is being lost to friction is increasing. And I can make a prediction about when the car is going to stop because the kinetic energy has fallen all the way to zero.

Another way of stating the second law of thermodynamics is to say that entropy or disorder tends to increase over time. What we can do then is we can put this graph into a basic formula form. We can say that the total energy is equal to the usable energy or free energy plus the unusable energy in the system.

## Summary

Hopefully, these examples helped you understand a little bit more about how the laws of thermodynamics apply to everyday life.

The first law of thermodynamics states that energy can be converted from one form to another, but energy can neither be created nor destroyed.

The second law of thermodynamics states that not all energy can be used, and disorder tends to increase over time. If you ever want to give you Mom a good excuse for your messy room, just tell her that you're only following the second law of thermodynamics.

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