Thermodynamics

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Big Ideas : Temperature, Heat, Thermal Energy, Specific Heat, Conduction, Convection, & Radiation.

Temperature can be a subjective idea. What is hot to one person may be cool to another. In science, temperature is measured by the motion of molecules in a substance. As the motion of molecules increases, or speeds up, the temperature of that substance increases. Objective scientific temperature is average kinetic energy of molecules. The average speed of all the molecules in a substance will determine how hot or cold a substance is.

Matter is composed of molecules which are tiny particles that have different combinations of atoms. Different molecules have different combinations of atoms. These molecules are in constant motion. How much motions, or kinetic energy, the molecules of a substance have determines the state of matter. For example, a water molecule (H20 – Two hydrogen atoms and one Oxygen atom) that has very low kinetic energy will be in a solid state; ice. A water molecule that is moving very fast will be in a gas state; water vapor or steam. This is known as the kinetic molecular theory .

Temperature is measured by three different scales, Celsius, Fahrenheit and Kelvin. The Kelvin scale is significant, because it sets zero as the temperature when all motion ceases. This is also called Absolute Zero.

Internal thermal energy is the sum of all the energies of a substance. The internal thermal energy of a substance is different than that the temperature of an object. A large ocean is often very cold, the molecules in the water are moving on average, with a lower kinetic energy than a boiling pot of water with very fast moving molecules. However, if you added all the molecules with their energies together of the cold ocean, it would be much greater than if you added all the energies of the molecules in a boiling pot. Thus, the ocean has a greater thermal energy (though it's temperature is lower) than a pot of boiling water.

Heat is the energy flow from a high temperature to a low temperature. Heat will ALWAYS flow from hot to cold. Some objects are more resistant to lose heat energy than others. Objects that very resistant to losing heat (or in other words, objects that retain heat best) have a high specific heat capacity. Specific heat is like an objects ‘thermal inertia' it is an object's resistance to an change in temperature. Water has a very high specific heat; it takes a long time for it to lose heat and it also takes a long period of time to gain heat. Hence, it is very resistant to a change in temperature. Steel, however, will heat up and cool down at a much faster rate. It has a low resistance to change in temperature, thus it has a low specific heat.

There are three different ways in which to transfer heat energy; conduction, convection, and radiation. Conduction is the transfer of heat by contact of two materials. Vibrating molecules will collide into neighboring molecules, transferring heat energy through contact. Some materials will transfer heat easier than others. Objects that transfer heat easily are called conductors; metals are good examples. Objects that transfer heat slowly are called insulators; air, wool, wood etc. are examples of good insulators.

Convection is the transfer of heat by flowing currents in a fluid (liquid or gas). Hot air rises (becomes less dense) and cools as it rises.

Radiation is the heat transfer by electromagnetic infrared waves. Unlike convection or conduction, these waves do not need a medium to move in. The most common source of radiation heat is from the infrared waves of the sun.

 Experiences Patterns Explanations Food added to hot water and to cold water   Adding hot nails to cold water Adding cold nails to hot water   Metal ball & Ring: A metal ball was heated and then attempted to push through a metal ring. Heating a wire with a weight hung in the middle of it. Heating both sides of a bimetallic strip.     Hand touching a metal pole in snow / Hand touching a wooden pole in snow.   Lighted Candle     Wind on a beach The coloring spread much more quickly in the hot water than in the cold water. The change in temperature of the nails was much higher than the change in temperature of the water. When the ball was heated, it could no longer fit through the ring. When the wire was heated the weight dropped. When both sides of the strip were heated, it always curved in the same direction.   The metal pole feel much cooler to the touch than the wooden pole.   The greatest amount of heat is felt directly above the flame. There is also heat felt on the sides of the flame. Wind on a beach will blow from the water to the land. The average speed of the molecules in the hot water are moving at a faster rate than in cold water. Water is more resistant to change in temperature than iron nails. Different materials have different capacity to retain heat energy.     In general, objects (especially metals) will expand when heated, and contract when cooled. Different objects will expand at different rates.       Different materials are better at conducting heat than others.   The hot air molecules rise (convection). Heat is also release through the sides by infrared radiation. Sand has a lower specific heat than water. As the sun radiates the land, the sand will heat up

Objectives

• Differentiate between internal energy, temperature, and heat
• Distguish between conduction, convection, and radiation as means of heat transfer
• Compare the specific heat of water with that of other substances
• Recognize the fact that most substances will expand when heated and contract when cooled.

 Monday Tuesday Wednesday Thursday Friday Journal: Science How does scientific knowledge affect your life? e.i. How does what you know affect what you do? Journal: No Journal Journal: Pre Mixed no class Journal: Heat Mixes (fill in the blanks from your lab) Activities: Reading from "A Matter of Degrees" On the back write a letter to George B. McClellan, the mayor of New York in 1906, asking for the release of Ota Benga using one arguement from science. Activites: Discuss Syllabus Temperature/Thermal Energy W.S. Activites: Heat Mixes I Heat Mixes II Activities Thermo quiz Specific heat reading Notes on Specific Heat