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Genny Mae Rowed

on 3 May 2010

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Transcript of Heat

HEAT By Emily Bolton and Genny Mae Rowed So.. What is heat? It's the transfer of mechanical energy from one object to another.
It's also called thermal energy. Well... So what? It is essential to everyday life. That's plants, animals, even people Heat is energy, and energy is work. All living things require
energy to live. Energy also forms and breaks chemical bonds.
We cannot survive long without proper heat; it is essential for everyday life. Humans cannot go for more than 24 hours without proper heat. Our bodies work best when they are within a narrow temperature range. If it goes beyond that range we, more or less, die. So, if there is no heat, we would die, but if there is too much, we would die as well
We use heat for most things in our everyday life. It sterilizes/kills bacteria, can be used to shape/make metals and plastics We also use it for electricity, burning natural gas, solar power, cooking, combustion, food manufacturing and it can be used as a catalyst.
What's the difference between heat and temperature then? Temperature is the measure for of the average kinetic energy of the individual atoms or molecules in a substance. It is not a measure of the amount of thermal energy Temperature is kinetic energy, while heat is thermal energy In the beginning One of the earliest theories of heat was proposed by Greek philosopher Empedocles, he believed all matter was made up of four elements, earth, air, fire and water. He believed many objects contained the element fire and that when they burned the fire inside was released, heat! Scientists discovered there were more elements than just earth, air, fire and water and a new theory was created. The phlogiston theory stated that substances that could burn contained an invisible fluid, phlogiston. It stated that as an object burned phlogiston flowed out. For example when wood burns all that remains after is ash according to the phlogiston theory that was because phlogiston had flowed out and the ash was all that was left. However when Magnesium and some other substances burned the ashes had more mass than the starting substance and if phlogiston flowed out how could the mass be greater? The caloric theory states that heat (called caloric) was a massless fluid in all substances. According to this theory heat (caloric) cannot be created or destoyed but can be transferred from substance to substance. Heat (caloric) flowed from hot objects to cooler objects. Joseph black developed a unit for the caloric, the calorie. The calorie was defined as the amount of caloric it takes to increase the temperature of 1g of water by 1 degree celsius. (today the calorie is defined as the amount of energy that must be added to increase the temperature of 1g of water by 1 degree celsius.) 492-435 BCE Early 1700's Late 1700's More Recently However when a hole was drilled in metal the shaving became hot, neither of the objects were hot before so were was the caloric coming from? Count Rumford's (Benjamin Thompson) theory based on this observation suggested there was no caloric substance. He stated that there was a relationship between the mechanical energy from the drill and the heat produced. His theory suggested the mechanical energy was converted to heat. 1789 Julius Robert Mayer found more evidence to support the relationship between energy and heat. Mayer discovered that people in the tropic have brighter red blood than people who live in cooler climates. The Brighter the blood the more oxygen, oxygen is used to break down food and to provide energy. People in cooler climates need to generate more heat, Mayer reasoned the same process that uses oxygen to provide energy must also provide heat, proving there is a relationship between heat and energy. 1814-1878 James Prescott Joule was working on a similar theory at much the same time but presented the concept just before Mayer. Joule preformed accurate measurements that related mechanical energy to heat. He measured the amount of energy transferred to water while increasing while increase the temperature of water by one degree celsius. 1818-1889 The work of Mayer and Joule led to the law of conservation of energy which states that energy cannot be created or destroyed, but it can be converted from one form to another. The Current Theory The Kinetic-Molecular Theory of Heat States that the kinetic energy or motion of the individual molecules in a substance determines heat or thermal energy. The molecules are in constant random motion and when the molecules are moving quickly the substance is hot, when the molecules move more slowly the substance is cooler. About 175 Americans die every year from extreme heat. Men are more prone to heat illness than women
because they sweat more and get dehydrated faster. Sun burn can slow the bodies ability to release any extra heat. "Facts About Extreme Heat." Louisiana Office of Emergency Preparedness. Louisiana Office of Preparedness, 16 April 2008. Web. 29 Apr 2010. http://gohsep.la.gov/factsheets/factsaboutextremeheat.html Gue, David, Glen Hutton, and Stephen Jeans. "Chapter 4: Thermal Energy and Work." ScienceFocus10. Whitby, Ontario: McGraw-Hill Ryerson, 2004. Print. Heat Through History
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