WORK DONE IN CLIMBING STAIRS (XV−3)

The problem. It is very difficult to make a satisfactory numerical estimate of the work which one may do in pushing a lawn mower, sweeping, pumping water, or shoveling coal. .The principal difficulty is in securing the necessary measurements of force and distance. However, it is not at all difficult to determine the amount of work done in climbing stairs, and this may be compared with other types of familiar work.

What to use. Yard stick, pair of scales, and stop watch.

What to do. 1. Previous to the experiment each member of the class should be weighed and the weight recorded to the nearest pound.

Height of stairway

FIG. 32

2. Measure the vertical distance (Fig. 32) from the bottom to the top of a stairway. Record in feet and tenths of feet. 3. Using the data secured in 1 and 2 calculate the number of foot pounds of work done by each member of the class in making the climb.

4. Let each member of the class actually make the climb up a stairway, walking at the usual rate, while others note the time consumed. Enter the data in the table and make all of the calculations suggested.

Questions. What factors are necessary in order to measure work? How do the rates of work compare with each other? If one horse power is equal to 550 foot-pounds of work per second what is your rate in this experiment? If a man works at the rate of one-seventh horse power, what is your rate in " man power"? What horse power would be required to operate an elevator lifting

the entire class at the average rate? Is it wise to run upstairs and use energy at a very rapid rate? Make a calculation to test your

conclusion.

Suggestions for report. Record all of the corrected calculations in a table and find the average horse power for the entire class.

Reference work. Read sections 193 to 196, 198, and 200.

Optional problems. What would be the efficiency in your case if you should carry 25 pounds to the top of the flight of stairs? Count the work done on the 25-pound load as useful work.

THE STEAM ENGINE (XVI-1)

The problem. The steam engine is a device for transforming the expansive force of steam into mechanical motion. These engines are usually classified according to the nature of the mechanism, to the manner in which the steam is used, or to the use to which the engine is put. Few inventions have influenced

modern life more than the steam engine. Land and sea transportation, the manufacturing industries, and the generation of electric power are all dependent upon the steam engine. How does it operate?

What to use. Ring stand, two rings, flask, jet tube, gauze, Bunsen burner, one-hole rubber stopper, pulley, and a model of a locomotive. If the model is not available use figure 33.

What to do. 1. By reference to your previous experience, a textbook in physics, a cyclopedia, or any other source, determine the ordinary names of the different parts of a steam engine and write these names near the proper letter in figure 33.

2. To see how the expansive force of steam may be transformed into motion, place a paddle wheel above a jet tube which is inserted in a flask (see Fig. 21). A suitable wheel can be made by cutting a metal pulley so that flanges may be turned aside. Heat the water in the flask until a vigorous jet of steam causes the wheel to spin. See if you can regulate the rotation of the wheel by changing the quantity of gas burned.

3. Next study the locomotive model as follows: Rotate the flywheel clockwise and bring the crank pin directly below the crank shaft (Fig. 33). Slide the reversing lever to the extreme right, and make a cross-section drawing of the cylinder and steam chest. Show the path of the live steam, the path of the exhaust steam, the direction of motion of the piston, and the forward or backward movement of the locomotive.

4. Rotate the crank pin clockwise one fourth of a revolution and repeat 2.

5. Rotate the crank pin an additional 90 degrees and repeat 2. 6. Study the model and arrange the locomotive to run in the opposite direction.

Questions. Trace all the changes from the burning gas to the spinning paddle wheel. What is the purpose of the slide valve? of the steam chest? How is the slide valve operated? Why has the flywheel a heavy weight? What is the purpose of the reversing lever?

Suggestions for report. File all of the drawings and written work in the notebook.

Reference work. Read sections 202 to 210. Make a list of the different types of steam engines that you have seen in operation.

Optional problems. Can you design and construct a small steam engine? Move the reversing lever to the left and work out 2, 3, and 4 as given.