Unit 2 Energy Flow in Technological Systems

1. Unit 2 Energy Flow in Technological Systems Chapters 4-6 P.138-253 And Chapter 10 P. 360 -398 SNAP P. 87 -155

2. In this unit we will explore: • Basic concepts of thermodynamics and mechanics • Types of energy • Energy conversions • Analysis of motion • Specific Heat Capacity • Heat of Fusion and Heat of Vaporization • Social and environmental issues

3. You will need to bring with you every day: • A pen and pencil • A calculator • A ruler • A protractor Note: Answers to Practice Problems from the text are in Apendix C (P.484)

4. Tips for success: • Come prepared. (bring all the appropriate materials) • Take down the examples! • Use your class time wisely. • Do the work. (Physics gets easier with practice. Homework questions often show up on exams)

5. Intro activity • Baseball bat physics • Volunteer will try and balance a baseball bat on the palm of his/her hand. • Which way is easiest to balance it? Why?

6. Chapter 4 Thermal Energy and workP. 140 -173 • Read article on “Turkey Power”

7. 4.1 The Development of Steam Engine • For thousands if years, people have known that when they boil water, the resulting steam exerts pressure and moves objects. • Hero’s steam engine (Pg 142) • Why did the steam cause the ball to spin? • Do Find Out Activity page 143 -Demo

8. Steam Engines • Steam engines are machines that generate steam and converts steam pressure into mechanical motion. How does a train steam engine work? How does the train move?

9. The First Practical Steam Engine • Savery’s Steam Engine • Thomas Savery, 1698 • Inefficient and costly Water boils in boiler producing steam Valves A and B are open but C and D closed, then the steam pressure can pump water to height h2 When the cylinder is full of steam, then valves A and B can be closed and D opened resulting in a vacuum vacuum causes water to rise height h1 from the mine shaft provided that height is less than 34 ft

10. Thomas Newcomen’s Engine, 1712 Fundamental Flaws • Constant heating and cooling caused rapid wear • Heating and cooling of cylinder made for a slow process

11. Read pages 144-145 and answer the following questions. • Watt’s steam engine is sometimes called a “double-acting” engine. What is acting twice during one cycle? • What is the purpose of the valve in Watt’s steam engine? • What reduces wear and tear on the piston in Watt’s steam engine? • How did Watt adapt his steam engine to perform tasks other than pumping water out of mines?

12. Read pages 144-145 and answer the following questions. • Watt’s steam engine is sometimes called a “double-acting” engine. What is acting twice during one cycle? • The pressure pushes the piston both ways. Since steam acts on the piston twice in one complete cycle, the engine is called a “double-acting” engine. • What is the purpose of the valve in Watt’s steam engine? • It moves one way to direct the steam to one side of the piston and then moves the other way to direct the steam to the opposite side of the piston. • What reduces wear and tear on the piston in Watt’s steam engine? • The cylinder in Watt’s steam engine is always hot, the cylinder and piston are not subjected to frequent heating and cooling. • How did Watt adapt his steam engine to perform tasks other than pumping water out of mines? • Watt invented systems of levers and a crankshaft that allowed the steam engine to turn a large wheel. A belt connected the wheel of the engine to other wheels, which could run many types of machines.

13. Watt’s Steam Engine Improvements: Piston and cylinder remained hot at all times Steam pressure produced was higher than one atmospheric pressure.

14. Steam Engines and the Industrial Revolution • Watt’s steam engine was adapted to drive many types of machinery and was responsible for the rapid development of the Industrial Revolution.

15. FYI • Many steam engines of the day, including Savery, Newcomen, and Watt’s used burning coal or wood as a source of energy. • Today steam engines are not used for locomotives, however, steam turbines still power ocean liners and cruise ships.

16. Steam Turbines • Steam passes through a set of curved blades similar to a fan. • Turns a central axle. • Pressure and temperature decrease as steam travels.

17. Do Check Your Understanding P. 149. # 1-6

18. 4.2 Scientific theories of HeatP. 150 - 163

19. Early Theories of Heat • Each early theory was an important step in the development of scientific knowledge. Theories and models were based on the knowledge of the time. • Only when new information became available that a theory was modified or discarded. • What other scientific theories have changed over time?

20. Empedocles(492 –435 B.C.E.) • All matter consists of four elements: earth, air, fire, and water. • Many objects contained fire. When these objects burn fire was released!

21. Phlogiston (Early 1700s) • Substances that could burn contained an invisible fluid called phlogiston. • The phlogiston flowed out of an object when it burned.

22. Caloric Theory (Late 1700’s) • Caloric was a mass-less fluid found in all matter. • It could not be created or destroyed, but could flow from one substance to another. • caloric always flows from warmer objects to cooler objects. • Unit – the calorie. • 1 cal. is the quantity of caloric that would increase the temperature of 1 g of water by 1° C.

23. Modern theories of heat • Benjamin Thompson (1753-1814) • First to reveal flaw in caloric theory • Was knighted and became known as Count Rumford.

24. Modern Theories of Heat Rumford Hypothesis (1798) : • Why did Rumford reject the current theory of heat? • Found the flaw by when a hole was bored into metal to make a cannon, the tools, metal and metal shavings became hot. Since none of the materials had been hot when the boring process began, what is the source of the caloric, or heat? Caloric is supposed to flow from warm to cool?

25. Rumford Hypothesis (1798) • There is no substance such as caloric. • some mechanical energy is converted into heat. “heat is equivalent to energy.”

26. Julius Robert Mayer (1840) • Found evidence supporting Rumford through bloodletting. • one of the first scientists to recognize that the body uses oxygen to break down food and use it for energy. • He reasoned that the same processes must also be providing heat. • “Heat is related to energy”

27. James prescott joules (1818- 1889) • Mayer wrote a paper on his discovery but it was overlooked due to poor quality of presentation. • James Joules, a physicist, also presented the same theory. • Ended up receiving the credit for discovering the mechanical equivalent of heat. • SI unit for energy named after him.

28. Energy and Work(pages 153-155) • Energy= the ability to do work • Work= the transfer of mechanical energy from one object to another • More than one force act on an object at the same time • Work done by different forces is reported separately.

29. Energy and Work(pages 153-155) • Compress a spring= • you do work on the spring and • transfer energy to the spring.

30. W = F • ∆d Wis the work in Joules (J) Fis the force in Newtons (N) ∆d is the distance in meters (m) Note: 1J = 1 N•m

31. Recall: Significant Digits: • The number of significant digits in an answer to a calculation will depend on the number of significant digits in the data. • For multiplication & division, the # of significant digits is determined by the # with the least amount of significant digits in the question. • For addition & subtraction, the number of significant digits is determined by the least precise number. i.e. you use the same amount of decimal places as the number with the least amount of decimal places.

32. Significant Digits Rules: • Non-zero digits are always significant • With zeroes: • Zeroes placed before other digits are not significant • Zeroes placed between other digits are always significant • Zeroes placed after other digits are significant

33. Example #1: • You exert 25 N of force on your textbook while lifting it 1.4m off the ground and placing it on a shelf. How much work did you do on your textbook?

34. Example #1: • You exert 25 N of force on your textbook while lifting it 1.4m off the ground and placing it on a shelf. How much work did you do on your textbook? F = 25 N ∆d = 1.4 m W = ?

35. W = F • ∆d = (25N)(1.4m) = 35 J Example #1: • You exert 25 N of force on your textbook while lifting it 1.4m off the ground and placing it on a shelf. How much work did you do on your textbook? F = 25 N ∆d = 1.4 m W = ?

36. Example #2 Working with Sci. Notation • The edge of space is defined as “the karman line” 100 km above the Earth’s surface. If 1.63 x 105 kN of force are required to launch the 2 029 203 kg space shuttle Discovery up to the edge of space, how much work is done?

37. Example #2 F= 1.63 x 105 kN x 1 000 = 1.63 x 108 N (x 1000 so move the decimal over 3 spots to the right) d = 100 km x 1 000 = 100 000 m = 1.0 x 105 m W = Fd = (1.63 x 108 N)(1.0 x 105 m) = 1.63 x 1013 J (add the exponents)

38. Do Practice Problems 1 to 9 P. 154 • Do BLM 4-5 energy and Work Practice Problems

39. You have a long metal tube that is curved. You also have a miniature golf ball that you are knocking into one end and out the other. How does the ball move after it leaves the other end of the tube? Does it move in a straight line or a curve? Perhaps it starts by moving in a curved line, then gradually straightens out? Or something else? A moment in science

40. Graphical Methods for Determining Work • Lets look at some position vs. force graphs. . .

41. This graph shows a constant force. • Area Under the graph: • Area of a rectangle equals length times the width. A = l • W • Length is the Force and the width is the distance. • A = F • ∆d • Area under the graph = Work!

42. This graph shows a changing force. • The area under the graph is work. • The shape under the graph is a triangle. • A = ½ b • h • Substitute d for the base and F for the height. • A = ½ d • F

43. Graphs with Non-uniform Shapes • This graph show a force increases rapidly, then falling back to zero. • How can you calculate total work done? • You can calculate total work done by calculating the work represented by each square on the grid, then counting the squares.

44. This graph show a force increases rapidly, then falling back to zero. • You can calculate total work done by calculating the work represented by each square on the grid, then counting the squares. There are 46 squares under this graph! A = b x h = 1m x 2N = 2 J 2 J x 46 = 92 J total.

45. How would you calculate work for this graph?

46. Graphs with non-uniform shapes

47. Your turn • What is the amount of work represented by this graph in J? Force (kN) Distance (m)

48. How would you calculate work for this graph?

49. Do Practice Problems 10 and 11 page 157 –158 • Do BLM 4-6 Graphical Methods for Determining work

50. A moment in Science Energy is neither created or destroyed: but it can be transformed from one form to another or one object to another.