Dignity of Labour free essay sample

This is followed by asking students to calculate their body’s energy needs for a day, both to perform various physical activities (including the climbing of stairs) and to maintain internal body functions. LEVEL: Middle Level (7, 8, and 9) DURATION: approximately 40 minutes STUDENT BACKGROUND: Students must be able to measure time with a stopwatch, measure distance with a meter stick, and enter data into and calculate with a spreadsheet. ADVANCE PREPARATION: Gather meter sticks and stop watches, arrange for use of computers and convenient staircase. MANAGEMENT TIPS: Elicit student responses to the Reflective Question before proceeding on to the activity. In checking student plans to measure and calculate the work they do climbing the stairs, make sure that students measure the distance walked up the stairs vertically, not along the slant of the stairs. They can determine their mass in kilograms by dividing their weight in pounds by 2. 2 and their weight in newtons by multiplying their mass (in kg) by the Earth’s gravitational field, approximately 10 N/kg. One way to administer the time measurements is to line up students on the landing at the foot of the staircase to be climbed. Have the last student time the first student, then have all other students timed by the student who has just climbed the stairs. (This allows all the timing by a single stopwatch, transferred among student timers at the top of the stairs. ) SAFETY: Require students to step on each step in order to reduce risk of injury. RESPONSES TO SOME QUESTIONS: In general, student answers to questions will vary, with differences in weight and in physical activities performed during the day. For example, a 175 lb. male of average build needs 175 x 12 = 2100 Calories per day to maintain internal body functions. The energy requirement for physical activity will vary greatly from student to student Teaching About Energy page 5. 1  ©2003 AAPT, John L. Roeder but probably be no more than 1000 Calories. An 80 kg student walking up a flight of stairs with a vertical height of 3. 0 m does 2400 Joules of work, which corresponds to 14. 4 kJ/min or 240 watts, if it is done in 10 seconds. The vertical average velocity is thus 0. 3 m/s, and the student’s kinetic energy in climbing the stairs is 3. 6 J, using vertical velocity only, far less than the potential energy gained. POINTS TO EMPHASIZE IN SUMMARY DISCUSSION: One outcome of this activity is a calculation of the amount of energy used by each student from food each day, both to maintain internal body functions and to perform physical activities. POSSIBLE EXTENSIONS: Once students have determined their need of energy from food for a day, students could be asked to inventory the energy content of the food they eat in a typical day and see how closely their consumption of energy from food matches their use of energy for internal body functions and physical activities. Teaching About Energy page 5. 2  ©2003 AAPT, John L. Roeder Name(s): _________________________________ Date: _______________ Period: ________ ACTIVITY 5. POWER OF A STUDENT Reflective Question: Write a response in your journal to the question in the box below. Discuss your response with others in your group. Can you arrive at a consensus in your discussion? Be prepared to report to your class the result of your group’s discussion. When you climb a flight of stairs, do you ever stop to think that you are pushing down on the stairs to lift yourself? By exerting this force to lift yourself, you are doing work on yourself, which shows up as an increase in your gravitational potential energy. The rate at which you do work is called power. Like the rate at which electric appliances transform electrical energy to other forms, power is expressed in joules/sec, or watts. With how many watts of power can you climb the stairs? Materials: meter stick stopwatch bathroom scale (optional) 1. Devise a plan to make the measurements and calculate the work you must do to climb a flight of stairs as well as the rate at which you do it (your power). Use standard metric units. After your teacher approves your plan, carry it out under your teacher’s direction. 2. Create an organized data chart showing the data you measured as you climbed the flight of stairs. 3. Create a detailed, step-by-step data analysis sheet showing what you did to calculate the power (in watts) with which you climbed the stairs. Climbing stairs is only one activity in which you do work – either on yourself or something else – during the day. This work is made possible because of the energy you gain Teaching About Energy page 5. 3  ©2003 AAPT, John L. Roeder from the food you eat. In fact, most of the energy from the food you eat goes to maintain your internal body functions, like maintaining your internal body temperature at 37 degrees Celsius. The energy from the food you eat is rated on nutrition labels in terms of Calories, and each Calorie of energy can increase the temperature of one kilogram of water by one degree Celsius. One Calorie is equal to 4180 joules (J), or 4. 18 kilojoules (kJ). The number of Calories per day needed to maintain your internal body functions can be found by multiplying your weight (in pounds) by 12 (if you are male of average build) or 11 (if you are female of average build), adding 5% if you are skinny, subtracting 5% if you are plump, or subtracting 10% if you are more than plump. * 4. According to the preceding paragraph, how many Calories do you need per day to maintain your internal body functions? In addition to energy for maintaining your internal body functions, you also need energy to perform various physical activities. The rates at which men and women use energy to perform these activities* are given in the following tables in terms of Calories per minute and kilojoules per minute: RATE AT WHICH MEN USE ENERGY activity driving a car washing dishes by hand typing quickly playing musical instrument at moderate rate walking, normal rate bicycling, easy rate skating, moderately swimming, moderate speed walking, briskly ping pong, brisk game walking upstairs, moderate rate tennis, average rate running, moderate speed bicycling, racing speed swimming, hard dancing, very vigorously running, cross country #Cal/min (man) 0. 7 0. 59 0. 59 1. 1 1. 8 2. 3 3. 5 3. 5 3. 5 4. 6 5. 3 5. 6 7. 6 8. 3 8. 7 9 9. 8 #min #Cal #kJ/min 1. 96 2. 47 2. 47 4. 60 7. 52 9. 61 14. 63 14. 63 14. 63 19. 23 22. 15 23. 41 31. 77 34. 69 36. 37 37. 62 40. 96 #kJ Teaching About Energy page 5. 4  ©2003 AAPT, John L. Roeder RATE AT WHICH WOMEN USE ENERGY ctivity driving a car washing dishes by hand typing quickly playing musical instr ument at moderate rate walking, normal rate bicycling, easy rate skating, moderately swimming, moderate speed walking, briskly ping pong, brisk game walking upstairs, moderate rate tennis, average rate running, moderate speed bicycling, racing speed swimming, hard dancing, very vigorously running, cross country #Cal/min (woman) 0. 43 0. 52 0. 52 0. 91 1. 5 2 2. 9 2. 9 2. 9 3. 8 4. 4 4. 7 6. 3 6. 9 7. 2 7. 8 #min #Cal kJ/min 1. 7974 2. 1736 2. 1736 3. 8038 6. 27 8. 36 12. 122 12. 122 12. 122 15. 884 18. 392 19. 646 26. 334 28. 842 30. 096 31. 768 33. 44 #kJ *Rates of Calories used are taken from Gerald Slutsky, â€Å"I Didn’t Know It Was Loaded,† in Energy: Options for the Future (Food and Energy), SUNY, Stony Brook, NY, p. F-17. 5. Enter the number of minutes per day you perform each activity, then calculate the number of Calories used by multiplying the #Cal/min by the number of minutes. The number of kilojoules per minute is obtained by multiplying the #Cal/min by 4. 18, and the number of kilojoules is obtained by multiplying the #kJ/min by the number of minutes. Enter your values into a spreadsheet like the one above and calculate the total number of Calories and kilojoules. 6. How does the total number of Calories or kilojoules for physical activity compare with the number of Calories or kilojoules needed for internal body functions (question 4)? 7. How does the rate of using energy (in kJ/min) to climb stairs at a moderate rate in the table above compare with the value you calculated in step 3 above? In the space provided, calculate and show how you change your answer from joule/second to kilojoules/minute before answering. Teaching About Energy page 5. 5  ©2003 AAPT, John L. Roeder 8. Could a difference between your measured value of energy rate (in kJ/min) to climb stars at a moderate rate and the value given in the table depend on the amount of kinetic energy you â€Å"gave yourself† in order to climb the stairs? Find out by measuring your average vertical speed. You may use the height you climbed on the stairs and the time you took to climb the stairs. Then use this speed to find your kinetic energy. You may look up the equation for kinetic energy if you need to do that. Show your calculations in the space provided. 9. How does your kinetic energy climbing the stairs compare with your potential energy increase? Teaching About Energy page 5. 6  ©2003 AAPT, John L. Roeder