What is humidity?

Met Office - Learn About Weather

15 Feb 202104:43

Summary

TLDRThis video script explores how weather affects hair texture, with high humidity causing straight hair to become wavy and curly hair to frizz. It delves into the science behind hair's sensitivity to atmospheric changes, mentioning the first hair tension hygrometer invented by Horace Benedicta Saussier in 1783. The script explains the workings of a wet bulb thermometer, which measures humidity by the rate of evaporation and condensation, and how it differs from a dry bulb thermometer. It also covers the concepts of relative humidity, dew point, and specific humidity, and how they relate to our perception of humidity and its impact on our comfort and hair.

Takeaways

🌧️ Weather conditions, particularly humidity, can significantly affect the appearance of your hair, causing straight hair to become wavy and curly hair to frizz.
💧 The bonding of hydrogen atoms in water molecules with proteins in hair leads to changes in hair shape, demonstrating hair's sensitivity to atmospheric humidity.
🧬 Human hair is so sensitive to humidity that it was used by Horace Benedict de Saussure in 1783 to create the world's first hair tension hygrometer.
🌡️ Modern methods for measuring humidity include the use of wet bulb thermometers, which differ from dry bulb thermometers by having a damp cloth around the bulb.
💦 The process of evaporation, which requires heat energy known as latent heat, is key to understanding how wet bulb thermometers measure humidity.
🚿 When you sweat, the latent heat of evaporation from the moisture on your skin helps cool you down, similar to how a wet bulb thermometer cools as it evaporates.
🌬️ The rate of evaporation from the wet bulb of a thermometer indicates the dryness of the air; the drier the air, the lower the wet bulb temperature compared to the air temperature.
🌫️ Relative humidity is measured when the rate of evaporation equals the rate of condensation, and it reaches 100% when the air is saturated with water vapor.
🌌 The dew point temperature is the point at which the air must be cooled for dew to form, indicating the temperature at which the air is fully saturated with water vapor.
🌬️ Specific humidity refers to the amount of water vapor in the air, measured in grams of water vapor per kilogram of air, influencing how humid the air feels.

Q & A

How does humidity affect hair?
-Humidity can cause straight hair to become wavy and curly hair to become frizzy. This is due to hydrogen atoms within water molecules bonding with certain proteins in the hair, altering its shape.
What is the role of hydrogen atoms in water molecules when it comes to hair?
-Hydrogen atoms within water molecules bond with certain proteins within hair, which can cause the hair to change shape in response to changes in atmospheric humidity.
Who built the world's first hair tension hygrometer and in what year?
-Swiss physicist and geologist Horace Benedicta Saussier built the world's first hair tension hygrometer in 1783.
What replaced the hair tension hygrometer for measuring humidity?
-The hair tension hygrometer was replaced by hygrometers that used charcoal, metal coils, and sheep's wool, and nowadays, a wet bulb thermometer is often used instead.
How does a wet bulb thermometer measure humidity?
-A wet bulb thermometer measures humidity by having its bulb wrapped in a damp cloth. The evaporation from the wet bulb causes it to cool down, and the rate of evaporation and condensation can indicate the dryness of the air.
What is latent heat and how does it relate to the feeling of cold after a bath or swimming?
-Latent heat is the heat energy required for water to evaporate. When we get out of the bath or a swimming pool, we feel cold because the evaporation of water on our skin takes away latent heat, helping us to cool down.
How does the wet bulb thermometer's temperature compare to the air temperature in dry air?
-In dry air, there won't be as much condensation, so it will take more evaporative cooling for equilibrium to be achieved, resulting in a lower wet bulb temperature compared to the air temperature.
What does it mean when the wet bulb temperature is the same as the air temperature?
-When the wet bulb temperature is the same as the air temperature, the rate of evaporation and condensation are already equal, indicating that the air is saturated and has 100% relative humidity.
What is the dew point temperature and how is it related to humidity?
-The dew point temperature is the temperature to which air needs to be cooled for dew to form. It is related to humidity as it indicates the temperature at which the air becomes saturated with water vapor.
How does specific humidity differ from relative humidity?
-Specific humidity is related to the amount of water vapor in the air, measured in grams of water vapor per kilogram of air. It differs from relative humidity, which is a percentage that represents the current amount of moisture in the air relative to the maximum amount of moisture the air can hold at a given temperature.
What factors determine how high the dew point needs to be for it to feel oppressively humid?
-The feeling of oppressive humidity depends on subjective factors, including the climate one is accustomed to and the amount of water vapor in the atmosphere, which affects the dew point.

Outlines

00:00

🌦️ The Impact of Humidity on Hair

This paragraph discusses how humidity affects hair texture. On humid days, straight hair may become wavy, and curly hair can frizz due to hydrogen atoms in water molecules bonding with hair proteins, altering its shape. Human hair is so sensitive to humidity that it was historically used to measure atmospheric conditions. In 1783, Horace Benedicta Saussier invented the first hair tension hygrometer, which was an advancement over previous hygrometers that used charcoal, metal coils, and sheep's wool. Modern alternatives to these include wet bulb thermometers, which measure humidity by the rate of evaporation from a damp cloth around a thermometer bulb. The paragraph explains the concept of latent heat, which is the energy required for water to evaporate, and how this affects our perception of temperature and the operation of wet bulb thermometers.

Mindmap

Keywords

💡Humidity

Humidity refers to the amount of water vapor present in the air. In the context of the video, it is discussed as a factor that can affect hair texture, making straight hair wavy and curly hair frizzy. The video also explains how human hair is sensitive to changes in atmospheric humidity, which can be used to measure it, as demonstrated by the hair tension hygrometer invented by Horace Benedicta Saussier in 1783.

💡Water Molecules

Water molecules are composed of hydrogen and oxygen atoms. The video mentions that hydrogen atoms within water molecules bond with certain proteins in hair, causing it to change shape. This interaction between water molecules and hair proteins is a key reason why hair behaves differently in humid conditions.

💡Hair Tension Hygrometer

The hair tension hygrometer is an instrument that measures humidity using human hair. As explained in the video, it was the world's first humidity-measuring device, built by Swiss physicist and geologist Horace Benedicta Saussier in 1783. It utilized the sensitivity of hair to humidity changes, replacing earlier hygrometers that used charcoal, metal coils, and sheep's wool.

💡Wet Bulb Thermometer

A wet bulb thermometer is a type of thermometer used to measure humidity. Unlike a dry bulb thermometer, which measures air temperature, a wet bulb thermometer has its bulb covered in a damp cloth. The video explains that the evaporation from the wet bulb causes it to cool down, and by comparing its temperature to the dry bulb temperature, one can determine the air's dryness.

💡Latent Heat

Latent heat is the heat energy required for a substance to change its state without changing its temperature. In the video, it is mentioned in relation to water evaporation. When sweat evaporates from the skin, it takes latent heat away from the body, helping to cool us down. This concept is also relevant to the wet bulb thermometer, as evaporation from its wet bulb is what causes it to cool.

💡Evaporation

Evaporation is the process by which water molecules change from a liquid to a gaseous state. The video describes how water evaporates from the surface of a liquid into the air, and how this process is affected by temperature. It also explains that when the air is dry, there is less condensation, leading to more evaporative cooling for the wet bulb thermometer to reach equilibrium.

💡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. The video explains that when the wet bulb temperature is the same as the air temperature, the air is saturated, and the relative humidity is 100%. It also discusses how relative humidity can affect the perception of humidity and comfort.

💡Dew Point

The dew point is the temperature at which air becomes saturated with water vapor and dew begins to form. The video uses the dew point to illustrate how the air's capacity to hold water vapor changes with temperature. It mentions that when the dew point and air temperature are the same, the air has 100% relative humidity, but it doesn't necessarily feel humid, depending on other factors.

💡Specific Humidity

Specific humidity is the amount of water vapor in the air, measured in grams of water vapor per kilogram of air. The video explains that higher specific humidity indicates more water vapor in the atmosphere, which can lead to a higher dew point and potentially more humid conditions. It is a measure of the absolute amount of moisture in the air.

💡Clouds and Fog

Clouds and fog are formed when water vapor in the air condenses into tiny water droplets around particles like dust. The video mentions this process in the context of air saturation and the formation of dew, illustrating how changes in air temperature and humidity can lead to the formation of clouds and fog.

Highlights

Bad hair days can be attributed to weather conditions, particularly humidity.

On humid days, straight hair may become wavy and curly hair can become frizzy due to water molecules interacting with hair proteins.

Human hair is sensitive to atmospheric humidity changes, making it a potential indicator of humidity levels.

In 1783, Horace Benedicta Saussier built the world's first hair tension hygrometer using human hair.

The hair tension hygrometer replaced earlier hygrometers that used charcoal, metal coils, and sheep's wool.

Modern humidity measurement often utilizes a wet bulb thermometer instead of the hair tension hygrometer.

Air temperature is measured by dry bulb thermometers, while humidity is derived from wet bulb thermometers.

Latent heat is the energy required for water to evaporate, which is why we feel cold when exiting a bath or pool.

Sweating is a body's reaction to heat, as the evaporation of sweat cools us down by removing latent heat.

A wet bulb thermometer's cooling is due to evaporation, which can indicate the dryness of the air.

Evaporation and condensation reach an equilibrium, which is affected by the temperature of the water and air.

The drier the air, the lower the wet bulb temperature compared to the air temperature, indicating less condensation.

When the wet bulb temperature equals the air temperature, the air is saturated, and the relative humidity is 100%.

The dew point temperature is the point at which air needs to be cooled for dew to form.

A dew point of 5 Celsius may not feel humid despite 100% relative humidity, due to the specific humidity of the air.

Specific humidity is related to the amount of water vapor in the air, influencing the dew point and perceived humidity.

The feeling of oppressive humidity is subjective and depends on factors such as climate and personal comfort levels.

The dew point's impact on hair and its perceived 'bad hair day' factor is subjective and open to individual interpretation.