Activity 1: Introduction to Physics 1104

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1 Name Section Activity 1: Introduction to Physics Ratio Reasoning Your instructor will discuss ratios and how they can be used to convert units. 1) Ratios used to convert units: a) Shake the plastic waterwheel until all of the red fluid is at the bottom. Turn the water wheel over and start the grey timer. Measure how many seconds it takes the red fluid to flow from the top to the bottom of the water wheel. Note: you may need to tilt the water wheel to move all of the red fluid to the bottom. seconds b) Suppose the water wheel contains 24 milliliters (ml) of red fluid. Use a ratio to find the rate of flow of the red fluid; that is, how many ml of fluid per second flow in the water wheel. (Note: for each answer, show your math steps and the units of the answer.) c) Next, use ratios to convert your answer to part b) from units of milliliters/second to liters/hour. 1 liter = 1,000 milliliters and 1 hour = 3,600 seconds d) How many gallons/hour of red fluid flow in the water wheel? 1 liter = gallons 1.2 Ratio Reasoning and Efficiency Your instructor will explain the use of ratios to find the efficiency of energy processes. 2) Ratios used to find efficiency a) Connect a hand-cranked generator to a tray of 4 small light bulbs. Turn the crank to light the bulbs. If each bulb is rated at 1 watt, how many watts of power are needed to light the bulbs? b) Suppose your body generated 35 watts of power while lighting the bulbs. Use a ratio to find the efficiency of this process. c) Group Discussion Question: What happens to the other 31 watts of power? Where do you think power was wasted in the process of turning the crank to generate electricity that lit the bulbs? 1

2 3) Efficiency of light bulbs Compare the relative efficiencies of an incandescent bulb and a compact fluorescent bulb. a) Use a wattmeter to measure the power required by an incandescent bulb. b) Measure the power required by a compact fluorescent bulb. c) Measurements have shown that each of these bulbs produce 3 watts of visible light. Calculate the efficiency of the incandescent bulb. d) Calculate the efficiency of the compact fluorescent bulb. e) How do the efficiencies of these bulbs compare? Use a ratio to determine how many times more efficient the compact fluorescent bulb is than the incandescent bulb. f) Group Discussion Question: Why is the compact fluorescent bulb so much more efficient than the incandescent bulb? 1.3 Scientific Notation and Powers of Ten 4) Scientific notation: Your instructor will discuss scientific notation. Scientific notation usually means writing one digit to the left of the decimal times the base 10 raised to an exponential power. For example, in scientific notation 275,000 = 2.75 x 10 5 a) An electric generating plant has input energy of 66,500,000 joules. Write this amount using scientific notation. b) Of this input energy, 37,900,000 joules of energy are wasted. Write the wasted energy using scientific notation. c) Find the joules of useful energy out. d) Calculate the efficiency of this process of generating electricity. 2

3 1.4 Linear and Exponential Growth Rates and Exponential Decay Your instructor will discuss linear and exponential growth and exponential decay. 4) Illustrating exponential decay a) Roll the 20 dice in the plastic cup onto your table and remove any dice that land with a 1 showing. Repeat for 20 throws, each time removing any dice showing a 1. After each roll, record below the number of dice left after you remove the dice showing a 1. When each table has completed 20 throws, we will combine the data for all groups. Roll Dice Dice Left Left Roll Your All table tables Dice Left Your table Dice Left All tables b) On the graph, using the totals for all groups, plot the number of dice left versus the number of rolls of the dice

4 c) Find the half-life of your graph. Show on the graph the steps you used. d) Group Discussion Question: Does your graph represent exponential decay? Does every downward curving graph represent exponential decay? What must be true of a graph line that indicates exponential decay or exponential growth? 4) Illustrating Exponential growth Source: a) Does the increase in wind power shown in the graph above represent exponential growth? If so, what is its doubling time? b) Does the increase in total renewable power shown in the graph above represent exponential growth? If so, what is its doubling time? c) Group Discussion Question: Explain how you determined your answers to parts a) and b) above. 4

5 Name Section Period 1 Exercises: Introduction to Physics 1104 Write answers to the questions below. Show your mathematical steps and the units of the quantities. This sheet with your answers should be turned in at the beginning of Period Using ratios to convert units: A hydroelectric power plant uses the energy of water flowing over a dam spillway to generate electricity. The water flow is measured at 3 x 10 5 liters per second. Use ratios to find the number of gallons of water per hour flow. (1 liter = gallons) Write your answer here using scientific notation: 2. Using ratios to find efficiencies: In the process of generating electricity at this hydroelectric plant, an input of 6 x 10 6 joules of energy results in 2 x 10 6 joules of wasted energy. What is the efficiency of this process? Write your answer here in the form of a percentage: 3. Using growth rates and doubling time tables: In 2012 a group of investors invested $100,000,000 in expanding this hydroelectric generating plant. Their invested money will earn an annual 4% return. Use data from Table 1.2 in textbook chapter 1 to find how many years are required for their investment to double. Then calculate how much their investment will be worth in the year 2065, assuming the rate of return remains at 4%. Show all the steps you used to find your answer. 5