Sociology homework help. Name_________________________________________________________________________

You have the Power

Introduction

The word work represents a concept that has a special meaning in science that is somewhat different from your everyday concept of the term. In science, the concept of work is concerned with the application of a force to an object and the distance the object moves as a result of the force. Work

(W) is defined as the magnitude of the applied force (F) multiplied by the distance (d) through which the force acts, W = Fd.

mgd

P t

d

F = mg

Figure 13.1

You are doing work when you walk up a stairway since you are lifting yourself through a distance. You are lifting your weight (the force exerted) the vertical height of the stairs (distance through which the force is exerted). Running up the stairs rather than walking is more tiring because you use up your energy at a greater rate when running. The rate at which energy is transformed or the rate at which work is done is called power. Power (P) is defined as work (W) per unit of time (t),

P = W

t

When the steam engine was first invented there was a need to describe the rate at which the engine could do work. Since people at that time were familiar with using horses to do their work, the steam engines were compared to horses. James Watt, who designed a workable steam engine, defined

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horsepower (hp) as a power rating of 550 ft·lb/s. In SI units, power is measured in joules per second, called the watt (W). It takes 746 W to equal 1 hp, and 1 kW is equal to about 1.33 hp.

Today let us calculate how much work you must do to “burn” Calories consumed. For example, a Peanut Butter Cup (pack of two and from the label) has 240 Calories per serving. My all-time favorite candy!

The following information will be needed in this activity for question 6.

Thermal calories are represented by “calorie” with a lower case “c”. The abbreviation is “cal”

Nutritional or dietary Calories are represented by “Calorie” with an upper case “C”. The abbreviation is Cal.

1000 calories = 1 Calorie

4.184 Joule = 1 calorie

We want to answer the question using the energy unit, Joule. For a peanut butter cup which has 240 Calories per serving, we can convert to Joules by the following calculations:

240 Calories = _________ Joules

240 Calories (1000 calories / 1 Calorie) = 240,000 calories

240,000 calories (4.184 J/ 1 calorie) = 1.004 x 106 J

Now let’s find out how much work you must do to “burn” off your favorite snack food Calories.

Procedure (SHOW ALL WORK!)

1. You, the Blue Raider, and another volunteer will measure the work done, the rate at which work is done, and the horsepower rating as you move up a stairwell. The volunteer will measure and record the data for you. First, write down the weight of the Blue Raider. measure and record the data for person A. An ordinary bathroom scale can be used to measure your weight. Record the weight in pounds (lb.) in Data Table. This weight is the force (F) needed by you to lift yourself up the stairs.

Your weight in pounds = _____________________________

Your weight in kilograms = __________________________

Assume that the acceleration due to gravity is implied. In other words, you do not need to calculate weight (w = mg) for this experiment. Assume that your weight is the force!

Also, you might need the following conversion: 1 kg = 2.20 pounds

2. The vertical height of the stairs can be found by measuring the height of one step, then multiplying by the number of steps in the stairs. Record this distance (d) in feet (ft) in Data Table.

Height of one step = ____________________ Number of steps = __________________________

Distance traveled in feet = _____________________________________

Distance traveled in meters = __________________________________

Recall that 1 m = 3.281 ft

3. Measure and record the time required for you to walk normally (and carefully!) up the flight of stairs. Your volunteer can do this on a cell phone. Record the time in seconds (s) in Data Table.

Time (walking) = ______________________

4. Measure and record the time required for you to run carefully up the flight of stairs as fast as can be safely accomplished. Record the time in seconds (s) in Data Table.

Time (running) = ______________________________________

5. Calculate the work accomplished, power level developed, and horsepower of each person while walking and while running up the flight of steps. Be sure to include the correct units when recording the results in Data Table.

Work = Fd (walking) _______________________________ Joules “burned” doing work

Work = Fd (running) _______________________________ Joules “burned” doing work

Power = Work / time (walking) = ___________________________________

Power = Work /time (running) = _____________________________________

You can find a conversion for horsepower in your textbook.

Horsepower (walking) = __________________________________________

Horsepower (running) = __________________________________________

6. Read the label on your favorite snack food. Use a different snack. Don’t forget units. Complete the following:

• Name of favorite snack = _________________________

• Calories per serving = ___________________

• Servings per snack = ___________________

• Total Calories per snack = ________________

• Convert the Total Calories to thermal calories. Show all work.

• Convert thermal calories to Joules. Show all work. This value is Joules Gained.

7. Compare your Joules gained (from the snack) to Joules burned (from the exercise). Which is larger? What does this tell you about food and exercise?

Results

1. Explain why there is a difference in the horsepower developed(but not in work) in walking and running up the flight of stairs. Use your data.

2. Work has the same units as energy. What does this tell you? Use your data. Explain your answer.

3. What did you learn from this activity? Use correct grammar, spelling and complete sentences.

Data Table

You have the Power

Walking Running

Weight (F)

(kg)

Vertical height

(d) of steps (m)

Time required

(t) to walk the flight of steps

(s)

Time required

(t) to run the flight of steps

(s)

Joules Burned (Work done)

W = Fd

(J)

Power

P = W/t

(J/s)

Horsepower developed

P ÷ 550 ft·lb/s

Joules Gained from snack

(J)