Introduction: (Initial Observation)
Dew is a thin film of water that has condensed on the surface of objects near the ground. Dew often forms on plants and metal objects during the nighttime hours and can be seen in early mornings while it is still cold. Surprisingly the amount of dew formed at different nights varies. Obviously some weather variables are affecting the amount of dew formed at each night.
Learning about dew may also help us to identify or predict other weather conditions. Possibly that is why in weather reports they usually announce a value known as dew point. What is de point, how it can be calculated and why it is important as a weather element is the subject of this project.
Find out about dew and how it forms. Read books, magazines or ask professionals who might know in order to learn about the factors that affect the amount of dew formed at different nights. Keep track of where you got your information from.
Following are some related information:
Dew point temperatures make clouds
What is the dew point and how can we measure it?
The dew point is defined as the temperature at which water vapor begins to condense. Condensation is the change of water from its gaseous form (water vapor) into liquid water. Condensation happens when air cools to the dew point temperature, and the water vapor in the air changes to liquid. Usually the air high up in the sky is cooler than on the ground, so that is where condensation happens. Condensation up in the sky makes clouds.
Dew points indicate the amount of moisture in the air. The higher the dew points, the more moisture there is in the air at a given temperature.
When the dew point temperature and air temperature are equal, the air is said to be saturated (meaning holding as much water vapor as it can). Dew point temperature is NEVER GREATER than the air temperature. Therefore, if the air cools, moisture must be removed from the air and this is accomplished through condensation. This process results in the formation of tiny water droplets that can lead to the development of fog, frost, clouds, or even precipitation.
Dew Point Temperature is defined as the temperature to which the air would have to cool (at constant pressure and constant water vapor content) in order to reach saturation. Dew points provide insight into the amount moisture in the air. The higher the dew point temperature, the higher the moisture content for air at a given temperature.
When the dew point temperature and air temperature are equal, the air is said to be saturated. Dew point temperature is NEVER GREATER than the air temperature. Therefore, if the air cools, moisture must be removed from the air and this is accomplished through condensation. This process results in the formation of tiny water droplets that can lead to the development of fog, frost, clouds, or even precipitation.
Relative Humidity can be inferred from dew point values. When the air and dew point temperatures are very close, this indicates that the air has a high relative humidity. The opposite is true when there is a large difference between air and dew point temperatures, which points to air with a low relative humidity.
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
What is dew point and how can we measure it? The purpose of this project is to learn about the factors that affect dew formation.
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
Variables that may affect the amount of dew are:
- Atmospheric moisture
- Weather temperature
Other variables such as air pressure, wind and light may also affect the dew formation, but we will not study them in this project.
In our experiments, moisture rate and temperature are called independent variables. Since dew formation depends on these variables, dew formation is a dependent variable. (Dew forms or does not form)
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
Write your hypothesis for this project. What do you think the dew point temperature will be? Do you think it will be warmer or colder than the air temperature? Do you think the dew point will be close to the air temperature or much different? If you repeat your experiment at a colder or warmer place will you get a different result? how different? What if you repeat your experiment in your kitchen with lots of moisture created by cooking and boiling water? Will you get a different result? how different?
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
The dew point is defined as the temperature at which water vapor begins to condense. In this project you will determine the dew point temperature for the air outside or inside. You will carefully cool a bucket of water until condensation forms on the outside. The temperature of the water when you see condensation is the dew point temperature.
- A bucket
- 3 gallons of water
- A cooler of ice
- 2 thermometers (Centigrade)
- a stirring tool
- data sheet and pencil
- Gather all of your equipment and go outside to a shady place.
- Start with a pail of water. The water should be the same temperature as the air temperature. (Put the pail of water outside several hours before)
- Measure and record the temperature of the air.
- Measure and record the temperature of the water.
- Add a small amount of ice to the water. Stir for one minute. Measure and record the temperature of the water. Write down the time. Observe the outside of the bucket.
- Keep adding small amounts of ice to the bucket, stir, record the temperature and time, and observe the outside of the bucket.
- Stop the experiment when you see condensation on the outside of the bucket. Record the time and temperature.
- Use the data that you recorded during this experiment to report dew point at the place of your experiment.
Materials and Equipment:
The list of material depends on your final experiment design and material that you can find for your experiment. This is just an example.
- A bucket
- 3 gallons of water
- A cooler of ice
- 2 thermometers (Centigrade)
- a stirring tool
- data sheet and pencil
For outside temperature, you can use a wall thermometer. For water temperature you must use a thermometer that can be immersed in water.
Some wall thermometers of MiniScience.com are also a Hygrometer.
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
If you do any calculations, write your calculations here.
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Your conclusion can also cover some new things that you have learned such as:
Dew forms when radiational cooling of these objects during the nighttime hours also cools the shallow layer of overlying air in contact with them, causing the water vapors to condense.
This condensation occurs because the capacity of air to hold water vapor decreases as the air is cooled. The temperature at which condensation begins, for a sample of air with a given water vapor content, is termed the dew point.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
Why do you think knowing the dew point might be important to weather forecasters?
Why do you think dew forms only at night?
Where did the droplets of water come from? What caused them?
As the wall of the container cools, it reaches a temperature at which the water vapor in the room air condenses into droplets. That temperature is the “dew point.” It changes from day to day depending on the “relative humidity” of the air.
Why do you think the “dew point” is named the “dew point”?
The “dew point” is the temperature at which water vapor in the air condenses into liquid, which is the phenomenon that forms dew on the grass.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.