Topography: Highs and Lows of the Earth's Surface (page 2)
Design Your Own Experiment
To measure a hill, stand on level ground at the base of the hill with your back to the hill. Hold the unmarked rod upright on the ground. Have your helper stand about 3 m away from you, facing you and the hill. Your helper should hold the marked rod upright so that the negative 10-dm mark is touching the ground and the string between the two rods is taut. Level the string by placing a line level (available in hardware stores) on the string near your rod. Instruct your helper to slowly move the ring up or down the marked rod until you can see the bubble in the center of the line level. This indicates that the string is level. Have your helper note the decimeter mark nearest the ring. The mark should be approximately zero. If the mark isn't zero, both you and your helper should very slowly move away from the hill until the ring at the end of the level string is at the zero mark (see Figure 2.3).
The base of the hill is interval 0, and the measurement is o dm. Record this measurement in a table similar to Table 2.1. To take the measurement for interval 1, have your helper put his rod in place of yours at the base of the hill. Then move up the hill about 3 m until the string is again taut. Level the string as before, have your helper note the decimeter mark, and record this measurement as interval 1. This and all uphill measurements should be positive numbers. Repeat this procedure, recording each 3-m interval up the hill until you reach the top of the hill. To take downhill measurements, have your helper put his rod in place of yours at the top of the hill. Then move down the hill until the string is again taut. Level the string and record the measurement as before. This and all downhill measurements should be negative numbers. Measure each 3-m interval down the hill until the measurement is again approximately zero and your helper has reached the base of the hill.
- You can measure the elevation of a small, gently sloping hill by using two rods, such as dowels or plastic pipes, each 2 m long. Using a pen and a meterstick, mark a circle around the center of one rod. Above and below this center mark, use the pen and the meterstick to mark every tenth of a meter, or decimeter (dm). With 0 at the center mark, first number every decimeter above zero as a positive number (1 to 10), then number every decimeter below zero as a negative number (–1 to –10). Tie a string at least 3 m long around the center of the unmarked rod. Stand the rods together so that the string around the unmarked rod is at the same height as the center mark on the marked rod. Secure the string with tape so that it cannot slide up or down the unmarked rod. Tie the free end of the string loosely to a ring, such as a jarring, that is larger than the diameter of the marked rod. Place the ring over the marked rod. Stand the rods about 3 m apart and adjust the knot around the ring so the string is taut.
- To map the profile (side view) of the hill measured in the previous experiment, follow the procedure described here for the data in Table 2.1 and the graph in Figure 2.4. Each square on the graph paper is equal to 5 dm, and each six squares across represent 30 dm, or 3 m, the measurement interval. The dots labeled 0 to 8 represent the measurements for intervals 0 to 8. Interval 0, the base of the hill, is marked by a dot labeled 0 in the bottom left corner. Each successive dot is placed six squares, or 3 m, to the right of the preceding dot. The dot is placed above the preceding dot depending on the interval measurement. Thus, because the measurement for interval 1 is 5 dm, the dot for interval 1 is placed one square, or 5 dm, above the dot for interval 0, and so on. The downhill or depression measurements are negative numbers and therefore are placed below the preceding dots. Thus, the dot for interval 5 is 2 cm below the dot for interval 4, and so on.
- Make a 3-D model of the hill by measuring and graphing the hill at a 90°angle to the first path. Cut out the two profiles from the graph paper and use these as patterns to cut the shapes from stiff paper. Make a vertical cut on each profile so they fit together. Cut one profile halfway down from the highest point; cut the other halfway up from the bottom. Fit the profiles together at a 90° angle.
Get the Facts
Cartography is the making or study of maps or charts. Find out more about mapping. What is a relief map? See H. J. de Blij, The Earth: An Introduction to Its Physical and Human Geography (New York: Wiley, 1995), pp. 15-26.
Warning is hereby given that not all Project Ideas are appropriate for all individuals or in all circumstances. Implementation of any Science Project Idea should be undertaken only in appropriate settings and with appropriate parental or other supervision. Reading and following the safety precautions of all materials used in a project is the sole responsibility of each individual. For further information, consult your state’s handbook of Science Safety.