What is relative humidity?

Summary

In 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.