What is relative humidity?

everWonder - about the world?

13 Aug 201702:30

Summary

TLDRIn the everWonder bits video, the concept of relative humidity is explored. Relative humidity measures the amount of water vapor air can hold relative to its maximum capacity at a given temperature. Warm air can hold more water vapor than cold air, which is why cooling air can increase its relative humidity to 100%, leading to condensation and phenomena like dew, fog, and rain. The video simplifies this process, using examples like opening a refrigerator door or coming inside on a cold day to illustrate how temperature changes affect humidity and can cause condensation.

Takeaways

🌬️ Humidity measures the amount of water vapor in the air.
💧 100% humidity means the air is holding the maximum amount of water vapor it can at a specific time and temperature.
🌡️ 'Relative' in relative humidity refers to the air's water-holding capacity, which changes with temperature.
🔥 Hot air can hold more water than cold air, with a cubic meter of air at 30°C (86°F) holding up to 30g of water, while air at 10°C (51°F) can only hold 10g.
📉 The relationship between temperature and water-holding capacity isn't linear, but the simplified values of 30g and 10g make it easier to understand.
☁️ When air reaches 100% relative humidity, it hits the dew point, and excess moisture will condense into water droplets.
🌧️ Condensation leads to phenomena like morning dew, fog, rain, and fogged glasses.
❄️ Cooling air down increases its relative humidity. For example, air at 30°C with 33% humidity can reach 100% humidity if cooled to 10°C.
🧊 Condensation occurs when warm air is cooled, such as when opening a refrigerator or going from the cold outside to a warm room, causing fogged glasses.
🌞 In warm, windy conditions, water evaporates faster, especially if saturated air is blown away, speeding up the drying process.

Q & A

What is humidity?
-Humidity is a measure of the amount of water vapor in the air.
What does 100% humidity signify?
-100% humidity means the air is holding the maximum amount of water vapor it can at a given temperature, not pure water.
Why is the term 'relative' used in relative humidity?
-The term 'relative' is used because the air's capacity to hold water vapor varies with temperature, making the humidity relative to the temperature.
How does air temperature affect its ability to hold water vapor?
-Hot air can hold more water vapor than cold air; for example, air at 30°C can hold up to 30g of water, while air at 10°C can only hold up to 10g.
What is the dew point?
-The dew point is the temperature at which the air becomes saturated with water vapor, reaching 100% relative humidity.
What happens when relative humidity exceeds 100%?
-When relative humidity exceeds 100%, the air can no longer hold all the water vapor, leading to condensation and the formation of dew, fog, or rain.
How can cooling air increase its relative humidity?
-Cooling air reduces its capacity to hold water vapor, so if air at 30°C with 33% relative humidity is cooled to 10°C, its relative humidity increases to 100%.
Why does opening a refrigerator door cause condensation?
-Opening a refrigerator door allows warm, humid air to enter and cool, causing the water vapor to condense on the cold surfaces, forming ice or frost.
Why do glasses fog up when you come inside on a cold day?
-The warm, humid air inside the glasses cools when exposed to cold air, causing the water vapor to condense on the lenses, fogging them up.
How does the sun and wind affect the drying of wet objects?
-The sun's warmth increases the air's capacity to absorb water, while wind helps to move saturated air away, speeding up the drying process.

Outlines

00:00

🌡️ Understanding Relative Humidity

The script introduces the concept of relative humidity, explaining that it is a measure of the amount of water vapor in the air relative to the maximum amount the air can hold at a given temperature. It clarifies that 100% humidity means the air is holding the maximum amount of water vapor it can at that temperature, not pure water. The script also explains that air's capacity to hold water vapor increases with temperature, using the example that 1 cubic meter of air at 30°C can hold up to 30 grams of water, while at 10°C it can only hold up to 10 grams. The concept of the dew point is introduced, where reaching 100% relative humidity leads to condensation, causing phenomena like morning dew, fog, and rain. The script also discusses how cooling air can increase its relative humidity to 100% and beyond, leading to condensation, using the example of opening a refrigerator door.

Mindmap

Keywords

💡Relative Humidity

Relative humidity is a measure of the current amount of water vapor in the air compared to the maximum amount the air can hold at a specific temperature. It is expressed as a percentage. In the video, relative humidity is central to understanding how the air's capacity to hold water changes with temperature. For instance, the script explains that 100% relative humidity at 30°C (86°F) is different from 100% at 10°C (51°F) because the air's water-holding capacity varies with temperature.

💡Water Vapor

Water vapor is the gaseous state of water and a key component of Earth's atmosphere. The script mentions that humidity is a measure of the amount of water vapor the air is holding. It's crucial for understanding relative humidity because it's the substance whose concentration in the air is being measured and compared to the air's capacity.

💡Temperature

Temperature is a measure of the average kinetic energy of the particles in a substance and plays a significant role in determining the air's capacity to hold water vapor. The video script emphasizes that hot air can hold more water than cold air, which is why temperature is essential in calculating relative humidity. An example given is that 1 cubic meter of air at 30°C can hold up to 30g of water, whereas at 10°C it can only hold up to 10g.

💡Dew Point

The dew point is the temperature at which air becomes saturated with water vapor and can no longer hold any additional moisture, leading to condensation. In the video, reaching the dew point is described as the point where the relative humidity is at 100%, and any cooling beyond this point would cause water to condense, forming dew, fog, or rain.

💡Condensation

Condensation is the process by which water vapor in the air turns into liquid water when the air cools down to its dew point. The script uses condensation to explain how water droplets form on surfaces like glasses or refrigerator walls when warm, humid air cools and can no longer hold the same amount of water vapor.

💡Atmospheric Pressure

Atmospheric pressure is the force exerted by the weight of air above a given area. Although it affects the air's capacity to hold water vapor, the script simplifies the discussion by suggesting that since most people experience similar pressures, it can be ignored for the purposes of understanding relative humidity.

💡Saturation

Saturation in the context of the video refers to the state where the air has reached its maximum capacity to hold water vapor at a given temperature. Any additional moisture would lead to condensation. The script explains that cooling air to its dew point or below will oversaturate it, causing water to condense.

💡Fog

Fog is a visible aerosol consisting of tiny water droplets suspended in the air at or near the Earth's surface. The video script uses fog as an example of condensation that occurs when the air becomes saturated with water vapor, especially during cooling.

💡Air Capacity

Air capacity, as discussed in the video, refers to the maximum amount of water vapor the air can hold at a given temperature. This capacity is not linear with temperature, and the video uses the example of 1 cubic meter of air holding 30g at 30°C versus 10g at 10°C to illustrate this point.

💡Wind

Wind is the movement of air from areas of high pressure to areas of low pressure. In the script, wind is mentioned as a factor that can affect the drying process by moving saturated air away, thus helping to evaporate water more quickly.

💡Evaporation

Evaporation is the process by which water changes from a liquid to a gas or vapor. The video script touches on evaporation when explaining how warm air can absorb water from wet surfaces, especially when combined with wind, which can speed up the drying process by moving the moist air away.

Highlights

Humidity is a measure of the amount of water vapor in the air.

100% humidity represents the maximum water vapor the air can hold at a given time, not pure water.

The term 'relative' in relative humidity indicates that air's water-holding capacity varies with temperature.

Atmospheric pressure's effect on humidity is generally uniform and can be disregarded for simplicity.

Hot air can hold more water than cold air, which is a fundamental principle in understanding humidity.

1 cubic meter of air at 30°C can hold up to 30g of water, while at 10°C it can only hold up to 10g.

The relationship between temperature and water-holding capacity is not linear.

Reaching 100% relative humidity at a given temperature is known as the dew point.

Exceeding 100% relative humidity leads to condensation, resulting in dew, fog, rain, or fogged glasses.

Cooling air with a relative humidity of 33% at 30°C to 10°C increases the humidity to 100%.

Further cooling oversaturated air causes water to condense.

Opening a refrigerator door demonstrates how warm humid air cools and condenses on cold surfaces.

Cold glasses fog up when entering a warm, humid environment due to the temperature difference.

Warm air can absorb water quickly, especially when wet items are exposed to sunlight.

Wind can speed up the drying process by moving saturated air away from wet surfaces.