Suggestions for report. DATE TIME WEIGHT LOSS PER HOUR Reference work. Read sections 142 and 143. Consult texts in botany or agriculture giving amounts of water given off by fields of crop plants. Optional problems. What is the source of the water constantly being transpired by growing plants? What becomes of this water? HOW LIQUIDS ARE TRANSFERRED BY THE SIPHON AND LIFT PUMP (XI-1) The problem. In the early days a single spring of water was often sufficient to furnish the required supply. Modern life has increased the demand for water from a few gallons per day to an average of more than 30 gallons per day per person for the medium-sized town. The average daily consumption per individual in New York is about 100 gallons. It is more than 200 gallons per day in Chicago. These demands make special devices necessary for transferring water. The Los Angeles watersupply system makes use of a great steel siphon. In some systems water flows by the force of gravity to its destination, while in others pumps must be used. What to use. Two wide-mouth bottles,` glass U-tube, water, six-inch calcium chloride tube, copper wire, cork, rubber sheet, rubber tubing, glass tube one foot long, ring stand, and burette clamp. FIG. 25 What to do. 1. Set up the siphon as shown in figure 25. Start the siphon by filling the tube with water, placing the finger over one end and inverting the other end in the bottle of water. Place the bottles on the table and compare the water levels when the water ceases to flow. Raise one bottle, then the other. 2. Assemble the model lift pump as shown in figure 26. See that the piston of sheet rubber fits the tube closely. Try to raise water from the bottle by moving the dry piston up and down. Pour some water on top of the piston and try to operate the pump. Improve the pump action until water flows from the spout at each upward stroke. 3. Note the three stages of operation as follows: (1) action on downstroke; (2) upstroke; (3) action of valves in (1) and (2). FIG. 26 Questions. Why must the siphon be filled with water? Why does the water remain in the tube when one end is closed? When does the siphon cease to operate? Why? What are the essential parts of a lift pump? Why does the pump lift the water? Explain 3. Suggestions for report. Make a crosssection drawing of the siphon and explain how it operates (see page 129 of the text). Make drawings to show the action of the valves in 3. Reference work. Read sections 147 to 149. Optional problems. Can you construct a force pump? Can you make a self-starting siphon? Examine an ordinary lift pump and make a diagram to explain its action. WHAT DETERMINES WHETHER OBJECTS FLOAT OR SINK? (XI−2) The problem. A submarine boat may float, travel under water at a given depth, or sink, depending upon the will of the crew and the perfection of the machinery. In a similar manner a balloon may rise in the air, travel at a given elevation, or descend to the earth. What is it that determines whether an object will float or sink in a fluid? What to use. Spring balance (250 grams); iron or carbon rod; piece of stone, coal, lead, brass, aluminum, tin, or other solid; string; water; and graduated cylinder (metric). What to do. 1. Use the apparatus shown in figure 27. Note whether the pointer of the balance is at zero. What is the value of the smallest division on the balance? Estimate the fractions of divisions if necessary. Weigh the object in the air. 2. Next weigh the object in water. 3. Fill a graduated cylinder about half full of water. Read accurately the volume of water. By means of a string lower the object into the water and read the volume again. Record the readings. FIG. 27 Questions. What mistakes are easily made in using a balance? What is the least weight that the balance will register? Explain why there is a difference between the weight of the object in air and its weight in water. What is the proper method for reading the water level in the cylinder? Why does lowering the object into the water change the level? Suggestions for report. Write complete answers to the questions given above. Corrected records of the experiment should be recorded in the table. Weight in air Loss of weight. Volume of water displaced Weight of water displaced. Weight of one cc. of object Reference work. Read sections 153 to 157. What is meant by density? A boy can lift a large stone to the surface of the water but not above the water. Why? Optional problems. What weight will the object weighed above lose in gasoline, kerosene, or milk? How can you find the density of a liquid? Does the density of a sugar solution change during boiling? Why? |