How Does Dew Form? Physics Behind Dew Drops and Fog
You might have seen on hilly areas, tiny drops rest on the cool surfaces at night. Also, you might have seen beautiful shiny drops on leaves during winters. Do you know what these two statements pertain to?
Well! We find dew on the cold surfaces and dewdrops form on the grass in winter that’s why we find a lustrous view on leaves.
So, do you know the following things?
How dew is formed?
How to dew?
Use of dew gauge to know about dew.
Difference between dew and fog
If not, this article will discuss how dew drops are formed with a dew factor and how to distinguish between dew and fog.
How are Dew Drops Formed?
We all are surrounded by air. This air contains moisture during the monsoon. At his moment, we call this air the humid air.
Now, when there is a temperature rise, this temperature rise leads to the evaporation of water, and the evaporations result in the formation of water vapours.
So, we understood that around us contains water vapours which we call moisture or humidity. Hot air contains more moisture as compared to cool air. During the chilled night when the hot air comes in contact with the cold surface, water vapour present in it condenses and takes the form of droplets, which is the exact dew definition.
In simple words, the hot air condenses and form tiny droplets that make a coating on the cold surfaces and the leaves of the grassland. A beautiful scenic view of the dew is shown below:
[Image will be uploaded soon]
Now, let’s understand the science behind the formation of dew:
Formation of Dew
Water vapour condenses into droplets relying on the temperature. The temperature at which droplet formation occurs is called the dew point. When the surface temperature drops, gradually reaching the dew point, atmospheric water vapour condenses to form small droplets on the surface, and that is how dew drops are formed.
From the above text, we understood how dew formed. Now, we will distinguish between dew and frost.
Difference Between Dew and Fog
So far we understood what is dew, but we are still left with the concept of fog.
Fog is a mist that we encounter while driving on hilly roads. We also hear in the news that due to the fall of an iceberg, the temperature may lower and that is the time when the days are unclear and mist tightly hugs the mountains. The unclear vision we find in the below image is the fog:
[Image will be uploaded soon]
The process of the formation of dew distinguishes it from hydrometeors, i.e., meteorological occurrences of water that form directly in the air that cools to its dew points (around condensation nuclei), and this is called the fog or frost. The thermodynamic principles of formation for both are the same. However, dew is usually formed at night.
Now, let’s discuss the difference between dew and fog in a tabular form:
Distinguish Between Dew and Fog
Important Facts
The occurrence of these tiny droplets on the ground results in difficulty among the players to have a grip on the ball. This difficulty is called the dew factor.
A Dew gauge is a device that measures the amount of dew on the surface.
Conclusion
Dew
Dewdrops are formed when water vapour condenses and it rests on the cold surfaces, metals, leaves, grasslands, and so on.
If we were to distinguish between dew and frost, dew is a tiny droplet that we are already knowledgeable about; however, when these condensed drops freeze further in a cold environment like Ladakh, Yukon, Verkhoyansk, Vostok; these droplets turn to frost.
Fog
Fog is something that appears to be close to the earth’s surface and we observe this beauty while driving in hill stations. However, the fog never rests on the surface, it remains in the air.
Fog is more often considered the mist that is a thick cloud of tiny water droplets covering the mountains.
FAQs on Dew in Physics: Definition, Formation & Fog Comparison
1. What is dew in the context of Physics?
In Physics, dew refers to the water droplets that form on exposed surfaces, typically outdoors overnight. It is not rain; instead, it is the result of atmospheric water vapor changing its state from a gas to a liquid. This process, known as condensation, occurs when a surface cools down to a specific temperature called the dew point.
2. What is the step-by-step process of dew formation?
Dew formation happens through a specific sequence of physical events:
Radiative Cooling: After sunset, surfaces like grass, leaves, and car roofs lose heat to the clear sky through thermal radiation and become colder than the surrounding air.
Reaching Dew Point: As a surface's temperature drops, it eventually reaches or falls below the dew point temperature of the air. The dew point is the temperature at which the air becomes saturated with water vapor.
Condensation: When the moist air comes into contact with these cold surfaces, it is cooled to its dew point. The water vapor in the air then condenses from a gaseous state into liquid water droplets directly onto the surface.
3. What is the fundamental difference between dew and fog?
The fundamental difference lies in where the condensation occurs. Dew forms when water vapor condenses directly onto a solid surface that has cooled below the dew point. In contrast, fog is essentially a cloud at ground level, formed when water vapor condenses around microscopic particles (like dust or pollutants) suspended in the air itself, not on a surface.
4. Why does dew form easily on clear nights but not on cloudy nights?
This happens due to the role of clouds in trapping heat. On a clear night, surfaces on the ground can freely radiate their heat into space, allowing them to cool down rapidly to the dew point. On a cloudy night, the clouds act like a blanket, reflecting the outgoing thermal radiation back towards the ground. This prevents surfaces from cooling sufficiently, and they often do not reach the dew point, thus inhibiting dew formation.
5. How is frost different from dew?
The key difference between dew and frost is the temperature of the surface when condensation occurs.
Dew forms when the surface temperature is above the freezing point of water (0°C). Water vapor condenses into liquid water droplets.
Frost forms when the surface temperature is at or below the freezing point (0°C). Here, water vapor bypasses the liquid state and transforms directly into a solid, a process called deposition or desublimation, creating ice crystals.
6. What is the “dew factor” in cricket and how does it affect the game?
The “dew factor” in cricket refers to the impact of dew formation on the playing conditions, especially during evening or night matches. The dew makes the ball wet, heavy, and slippery. This significantly affects the game in several ways:
Bowling Difficulty: It becomes hard for bowlers to grip the seam of the wet ball, reducing their ability to generate pace and spin.
Batting Advantage: The wet ball tends to skid off the pitch, coming onto the bat nicely for the batsman and making it harder for bowlers to use variations.
Fielding Challenges: The outfield also becomes wet and slippery, slowing down the ball and making it difficult for fielders to move and throw accurately.
7. Can dew form on a windy night? Explain why or why not.
It is less likely for significant dew to form on a windy night. Wind mixes the air, preventing a stable layer of cold air from forming near the ground. This constant circulation of air makes it difficult for any single surface to cool down to the dew point and stay there. For dew to form, calm conditions are ideal, as they allow a layer of air in contact with a surface to cool undisturbed until condensation occurs.
