Heat+-+Thermodynamics

Heat and Thermodynamics

Objectives:
 * Describe the three processes through which heat is transferred.
 * Identify real life examples of heat transfer by each of the three methods.
 * Develop a working understanding of what the Laws of Thermodynamics are.

Essential questions:
 * 1) What are conduction, convection and radiation?
 * 2) How do conduction, convection and radiation work? Use a boiling pot of water for all three forms of heat transfer or an application of your choice.

Heat is a form of energy and therefore it obeys all of the laws that we commonly associate with other laws regarding energy of any type. For example; energy is neither created or destroyed, this is the First Law of Thermodynamics it is also commonly referred to as the Law of Conservation of Energy.

If you put a few ice cubes into a cup of hot coffee or tea the ice cubes will melt rapidly. Why? The heat from the liquid and the cold from the ice cubes will attempt to reach equilibrium (the same temperature). The heat energy from the rapidly moving molecules that make up the hot water banging into the much slower moving water molecules in the ice cubes.

Here's a YouTube clip that gives an excellent introduction to heat transfer. media type="youtube" key="k9M4y6w0Ehw" height="344" width="425"[]

Following are still picture examples of each of the three types of heat transfer.

Conduction is one of those lessons you usually only have to LEARN once. If a young child touches a hot pot on the stove or you eat a bite of food that is too hot for our senses you are experiencing pain through conduction. The object with more heat transfers it's energy __**through contact**__ to the object with less heat energy. Ouch! The pot in the picture below is heated by being in direct contact with the metal plate that is between the fire and the pot, not directly by the fire. **__Through contact__** is the point to focus on here.



Convection is __**how heat is transferred through fluids**__. If you apply a flame to a pot of water the water at the bottom of the pot gets hot first due to direct contact with the pot that is heating through conduction. As the water that gains energy (gets hot) it expands because the molecules are moving much faster than the surrounding cooler water molecules. The water molecules that are expanding become less dense than the surrounding molecules, so they rise to the surface. An analogy is if you take a breath and hold it in a pool you will float in a pool since you are less dense than the water, if you exhale you will sink because you become more dense than the water. As the hot water rises it pushes the colder water up then out towards the sides of the pot. As the hot water reaches the surface the water cools slightly. The reason for this follows in the radiation section. As the water cools it creates a cycle due to the water that is currently being heated at the bottom of the pot. Since this is a cycle the process repeats itself.

Convection is not only responsible for the occurance of weather **(air is considered a fluid),** but it is also the leading theory of how the Earth's surface is manipulated by plate tectonics. We can see examples at active volcano sites. The extremely hot magma (lava) to rise to the surface due to convection.

[]

Radiation is __**heat energy transferred through not direct contact**.**​**__ Imagine a warm sunny day at the beach, the waves crashing violently on the shore. As you lie on your blanket slathered in 50 SPF sunblock you realize that you are becoming quite warm. Radiation is the reason why. The sun's rays composed of heat and light are transferring energy through the direct contact of air molecules in between you and the sun. As the rays continue to transfer their energy to you, your body becomes much warmer. Going back to the boiling water in the pot example, the molecules that reach the surface of the water transfer their energy to the air molecules directly above, warming the air.

In the illustration below radiation is shown by the wavy lines.

[]

Here's one take on the First and Second Laws of Thermodynamics (they sound somewhat imposing but they aren't that bad). The Star Wars pictures could be connected to the Laws but that is probably a discussion for another time and wikispace. Just try to listen to the lyrics, I have a link to the written lyrics following the clip.

media type="youtube" key="Cb2kBFqrZx8" height="344" width="425"[]

Here is the link to the lyrics. http://www.iankitching.me.uk/humour/hippo/entropy.html

This is a good, easy to read (mostly) explanation (no pictures) of the basics of thermodynamics. I apologize in advance for the title of the site, there aren't any rants against evolution I just found it to be a good explanation.

http://www.scienceagainstevolution.org/v7i1f.htm

Here is an example that **shows** one of the most basic level of thermodynamics. Reading the text helps but the picture explains that heat is energy. The object on the left has more heat energy than the object on the right. We can tell this by looking at the thermometer on top of either object.

[]

This website shows us a practical real-life example of how thermodynamics effects all of us everyday. The site explains how thermodynamics is responsible for driving the forces of weather that effects us all.

[]

Okay so the weather is determined by and physics majors/ engineering students are concerned with the concept of thermodynamics. Why should you care? This site provides a great explanation that applies to everyone who dosen't live on a tropical island where the temperatures never drop below 70 degrees F. []

A link to a popular college exam question response posted on the internet dealing with the concept of thermodynamics. Skip this if you are easily offended.

[]