Dignity of Labour

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ACTIVITY 5. POWER OF A STUDENT (Teacher’s Notes) PROCESS SKILLS: Measure, Observe, Compare, Test, Explain OBJECTIVE: The objective of this activity is to motivate the concept of power, or rate at which energy is transformed, and to apply it to the rate at which students do work to increase their gravitational potential energy in climbing a flight of stairs. IDEA: Students are asked to measure their gain in gravitational potential energy as they climb a flight of stairs, then to calculate the rate at which this potential energy is gained. 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

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©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

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©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...
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