Relative Humidity of the Earth’s Atmosphere: A Simple Experiment

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NATS 1780 Lab: Relative Humidity of Earth’s Atmosphere Purpose: The purpose of this lab is to investigate the concept of capacity through a simple physical experiment. The experiment is subsequently reframed as a physical model that can be applied to understanding humidity in Earth’s atmosphere. Materials: You will need the following: ● 1 cup of rice (minimum) ● water ● a measuring cup or scale ● a small pot with a lid ● a recipe Notes: 1. Feel free to use any type of rice, or to substitute pasta, noodles or even quinoa, legumes (e.g., lentils), couscous. Yes, even Ramen noodles are acceptable! 2. A measuring cup allows you to measure both the amount of rice and the amount of water using the same units - e.g., cups, fluid ounces, millilitres, … If you do not use the same units, you will need to make conversions. Procedure: 1. Divide your rice into three equivalent amounts. 2. Experiment 1 a. Take the first third of your rice. b. Match the rice with the amount of water detailed in your recipe. c. Hypothesize the doneness of your rice, and the amount of water you expect to be left over at the end, before you begin cooking. d. Cook your rice to perfection. (It should be perfect since you followed a recipe, right?) You should only be lifting the lid to stir the rice occasionally. e. Fill in a table, similar to the one below, for this experiment. 3. Experiment 2 a. Take the second third of your rice. b. Match the rice with twice the amount of water detailed in your recipe. c. Hypothesize the doneness of your rice, and the amount of water you expect to be left over at the end, before you begin cooking. d. Cook your rice. You should only be lifting the lid to stir the rice occasionally. © L. I. Lumb - Sharing prohibited. Violators subject to legal and/or academic consequences. 1 e. Add the entries for this experiment to your table. 4. Experiment 3 (Optional) a. Take the final third of your rice. b. Match the rice with half the amount of water detailed in your recipe. c. Hypothesize the doneness of your rice, and the amount of water you expect to be left over at the end, before you begin cooking. d. Optional: Cook your rice. You should only be lifting the lid to stir the rice occasionally. e. Add the entries for this experiment to your table. 5. Additional Experiments a. Not required, but a great way to take advantage of group work! Parameters> Experiments Rice (units) Water at Start (units) Cooking Time (minutes) Water at End (units) Doneness (under, perfect, over) Experiment 1 Hyp: None Actual: Hyp: Perfect (light/fluffy) Actual: Experiment 2 Hyp: ??? Actual: Hyp: ??? Actual Experiment 3 (Optional) Hyp: ??? Actual: Hyp: ??? Actual: Part 1: Analysis Questions Based on your experiments, answer the following questions: 1. Are you quantifying amounts (of water and rice) as volumes, masses, or something else? 2. State the ratio of the amount of water at the start of your experiment to the amount of rice. For example, if you started with a 250 mL of water and 1 cup of rice, the ratio would be 250 mL / 1 cup. Do this for each experiment. 3. State the ratio of the amount of water at the start of your experiment to the amount of rice. For example, if you started with a cup of water and a cup of rice, the ratio would be 1:1. Do this for each experiment. 4. State the ratio of the amount of water at the start of your experiment to the amount of rice as a decimal value. For example, if you started with a cup of water and a cup of rice, the decimal-value ratio would be 1.0. Do this for each experiment. © L. I. Lumb - Sharing prohibited. Violators subject to legal and/or academic consequences. 2 5. Express the ratio of the amount of water at the start of your experiment to the amount of rice as a percentage. For example, if you started with a cup of water and a cup of rice, the percentage would be ( 1 cup H2O(l) / 1 cup rice ) x 100% = 100%. Do this for each experiment. 6. Express the ratio of the amount of water at the start of your experiment to the amount of water plus rice as a percentage. For example, if you started with a cup of water and a cup of rice, the percentage would be ( 1 cup H2O(l) / 2 cups H2O(l) plus rice ) x 100% = 50%. Do this for each experiment. 7. Determine the amount of water plus rice at the start. Subtract the amount of water left over at the end. Call this the normalized amount of water plus rice. Express the ratio of the amount of water at the start of your experiment to the normalized amount of water plus rice as a percentage. For example, if you started with a cup of water and a cup of rice, and had ¼ cup of water left over at the end, the percentage would be ( 1 cup H2O(l) / 1¾ cups H2O(l) plus rice ) x 100% = 57% (approximately). Do this for each experiment. 8. Do your answers for questions 6 or 7 match more closely with your answers for Question 5? 9. Define the capacity of your rice as the decimal-value ratio you calculated for Experiment 1 in Question 4. Express the decimal-value ratios for experiments 2 and 3 relative to this capacity as a percentage. For example, suppose the capacity from Experiment 1 results in a decimal-value ratio of 1.0. Suppose the decimal-value ratios for experiments 2 and 3 are 0.5 and 2.0. Then, the relative capacities for experiments 2 and 3 are 0.5/1.0=0.5=50% and 2.0/1.0=2.0=200%. 10. How was the end of each experiment determined? 11. What happens to the water during the cooking process? Create a source-process-sink diagram to capture this. 12. Why is a stove required? 13. Why is a lid for the pot used? Exp. 1 Exp. 2 Exp. 3 End? Ratio (water/rice) Ratio (water:rice) Ratio (water/rice as %) Ratio (water / (water+rice) as %) Ratio ( water / (normalized water+rice) as %) Relative capacity (%) © L. I. Lumb - Sharing prohibited. Violators subject to legal and/or academic consequences. 3 Part 2: Application Questions Your experiments describe a physical model for Earth’s atmosphere. Your rice corresponds to an atmospheric air mass, and your water to water vapour in Earth’s atmosphere. In the same way that rice absorbs water in your experiments, Earth’s atmosphere has a capacity for water vapour. Your model also provides physical analogs for the atmospheric notions of: ● Saturation - Under, perfect and over doneness ● Absolute humidity - Question 2 ● Specific humidity - Question 6 ● Relative humidity (RH) - Question 9 Note: The notion of capacity (Question 9) is defined indirectly in the case of relative humidity for Earth’s atmosphere - through use of Saturation Vapour Pressure (SVP). As a consequence, the familiar notion of humidity (e.g., a humid Summer’s day) turns out to be quite technical when approached from a scientific perspective. By applying your experiments, answer the following questions: 1. What does your answer to Question 8 suggest about the capacity of Earth’s atmosphere for water vapour? 2. Does relative humidity provide us with the actual amount of water vapour in Earth’s atmosphere? 3. Why might atmospheric scientists tend to make use of relative humidity in practice? 4. If Earth’s atmosphere is regarded as a sink for water vapour, identify at least one source. Identify the process involved in transferring from source to sink. Represent all of this using a source-process-sink systems diagram. Your Submission Submit your experimental results plus the answers to your questions online via Moodle. Feel free to use visuals (e.g., sketches, photos, …) Note: You are encouraged to work together on labs. However, your submission must be original. Translation: Write up your final lab submissions independently, using your own words. Assessment: This is a pass/fail component of the course that accounts for 2.5% of your overall grade. Completing at least 75% of the lab appropriately will result in a “Satisfactory” assessment and a grade of 2 out of 2.5; an “Outstanding” assessment, and a grade of 2.5 out of 2.5, will be awarded to those who completed at least 90% of the lab appropriately. © L. I. Lumb - Sharing prohibited. Violators subject to legal and/or academic consequences. 4