Personal Work and Power Lab

Transcription

1 Personal and Power Lab Purpose: In this activity, we will experience the concepts of and Power using simple materials. Complete the following activity in your group. Part One: Calculating & Power Supplies: 1-6m long piece of string or twine. 6 metal weights 1 plastic zip top baggie Small Digital Scale as needed Spring scale as needed Bathroom Scale as needed Meter stick & 1 ruler (one to measure with and the other to be the dowel rod ) Calculator as needed Stopwatch Duct tape or masking tape Calorie information for a food item Procedure: Calculate the work and power that you can do with your arms and legs. Part One Section A: ARMS 1) Find the mass of the metal weights and record in the table (remember to convert it from g to kg) find the mass of the baggie and add it to the total for the 6 metal weights. The baggie = kg, each weight = kg 2) Use the spring scale and hang them from it in the baggie to find the force of gravity (weight) of the metal weights and record that in the table. 3) Find the distance from the ground floor to the 2 nd story railing and record it in the table 4) Poke a hole (or two) in the baggie and lace the string through it on one end. Place the weights inside the baggie. 5) Duct tape the other end of the string so that it is securely attached to the middle of one of your dowel rod. 6) Measure the length between where the string is duct taped and the bottom of the baggie this is the distance the weights will be pulled up. 7) Time how quickly you can raise the mass by wrapping the string around the dowel rod. Do this once slowly and another time more quickly and record the time in the table. 8) Calculate the work and power that was produced from this activity and record your data in the table below. Mass of the baggie of 6 metal weights (kg) Distance (m) Force of gravity on baggie of 6 metal weights (N) Time slow (sec) Time quick (sec) Power slow (W) Power quickly (W)

2 Part One Section B: LEGS 1) Each group member will get their weight in pounds from the bathroom scale (if this is an issue with some members, they can use a weight that they choose instead). 2) The weight in pounds will be multiplied by 4.4 to get the weight in Newtons. The group will use the Second Law formulas to solve for mass in kg. 3) Determine the vertical distance in meters from the first floor to the second floor. To do this, measure the height of each step and count the number of steps between the first and second floor. (or you can hang a string and measure from the top floor down to the bottom floor) 4) With a stopwatch, a) Measure your time slowly up the stairs to the second floor b) Measure how quickly you can get from the first floor to the second floor. 5) Record your weight (Newtons) and time (seconds) the data table below. 6) Calculate the work and power that was produced from this activity and record your data in the table below. Mass of (kg) Distance (m) Weight of (pounds) Force of Gravity on (N) Time - slowly (s) Timequickly (s) Power slowly (W) Power quickly (W)

3 PART TWO: Burning Off Calories Supplies: 1. a candy bar or other food item with calorie total listed on the packaging 2. calculator Procedure: Food item A for group member is Food item B for group member is Food item C for group member is 1. Record how many Calories are in the food item per serving based on the label. Calories per serving in item A = Calories. Calories per serving in item B = Calories Calories per serving in item C = Calories 2. The human body is only about 30 % efficient at best in digestion, so how many Calories at best can the human body get out of that candy bar? Find the actual calories by multiplying the previous value by 0.3 Actual Calories per serving item A = Calories Actual Calories per serving item B = Calories Actual Calories per serving item C = Calories 3. In the data table record the work done to wind the weight up the string earlier, as well as the work done by each person going up the stairs (you calculated both in earlier parts of the lab). 4. In order to calculate how many Calories are burned doing the work, divide the number of Joules of work done by 4186, since there is 4186 J to 1 Calorie. Do this for both the work done pulling up the weight on the string and for the work done by going up the stairs. Record this information in the table for going up the stairs and for pulling up the weight on the string. 5. To find the number of times the string must be wound to burn off the actual Calories per serving use the following formula: Actual Calories per serving The number of reps needed = Calories burned by pulling the weight up 6. Calculate the number of times going up and down the stairs needed to burn off the Calories in one serving using the following formula (note: we will multiply the work done going up by 2 to account for the round trip down the stairs): The number of trips up and down the stairs = Actual Calories per serving (2 Calories burned while going up the stairs) 7. Eat your food item (The data table is on the next page)

4 Actual Calories consumed in one serving (Cal) performed pulling weight up the string Calories burned by pulling weight up string (Cal) Number of times the string will be wound to burn the calories in the serving done by going up the stairs Calories burned by going up the stairs (Cal) The number of trips up and down the stairs to burn off the serving Part Three: Post Lab Questions 1.) Two people of the same mass climb the same flight of stairs. The first person climbs the stairs in 25 seconds. The second person takes 35 seconds. Which person does the most work? Which person expends the most power? Explain your answers. 2.) A box that weighs 1000 Newtons is lifted a distance of 20.0 meters straight up by a rope and pulley system. The work is done in 10.0 seconds. What is the power developed in Watts and kilowatts? 3.) A person of mass 64 kg climbs up a ladder to a height of 5.0 meters. a.) What work does the person do? b.) If the person did the work in 3 seconds, how much power did they use? LAB ANALYSIS QUESTIONS: 1) Which activity required the most work? Explain why. 2) Which activity produced the most power? Explain why. 3) If you wanted to produce more power, what could you do to maximize power? 4) What could be done to use more calories (or joules) of energy from food?

5 Part Four: Graphing Construct a bar graph of the Power for each group member Each group will either graph A) Power pulling up metal weights or B) Power climbing stairs for each group member For each group member there will be 2 bars (climbing stairs slow & climbing stairs fast or pulling up the metal weights slow & pulling up the metal weights fast) Make sure to include all the usual parts of a bar graph especially a legend for the bar colors

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