What is humidity?

Summary

This 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.