Embedded Files
Water
Water
Water's States of Matter
Water's States of Matter
Water is one of the few substances on Earth that naturally exists in all three common states of matter: solid, liquid, and gas. You see these states every day—often without realizing it.
Solid:
When water is cold enough (below 0°C or 32°F), it freezes and becomes ice. The molecules slow down and lock into a fixed structure, giving ice a definite shape and volume.
Liquid:
Between 0°C and 100°C (32°F to 212°F), water is a liquid—the form we drink, swim in, and see in lakes and oceans. In this state, molecules move freely but stay close together, so water takes the shape of its container but maintains a definite volume.
Gas:
When water reaches 100°C (212°F), it boils and becomes water vapor, a gas. In this state, molecules move very quickly and spread far apart. You can’t see water vapor directly, but you can see steam—tiny droplets of liquid water forming as vapor cools. In this state, water has no definite shape or volume.
Water's Changes of State
Water's Changes of State
Water changes from one state to another through energy being added or removed:
Melting: Ice absorbs heat and becomes liquid water.
Freezing: Liquid water loses heat and becomes ice.
Evaporation: Liquid water absorbs heat and turns into water vapor (this happens even below boiling point—like a puddle drying).
Condensation: Water vapor loses heat and becomes liquid water (this forms clouds, dew, and fog).
Sublimation and Deposition: Under certain conditions, ice can turn directly into vapor (sublimation) or vapor can turn directly into ice (deposition), like frost forming on a cold morning.
Humidity
Humidity
When we talk about how “humid” it feels outside, we’re really talking about the amount of water vapor in the air. Humidity is simply the actual amount of water vapor in the air, no matter the temperature. If the air contains more water vapor, the humidity is higher—simple as that.
Relative Humidity
Relative Humidity
Relative humidity describes how full the air is with water vapor compared to how much it could hold at that temperature (water vapor capacity). Warmer air can hold more water vapor, while colder air can hold less.
Relative humidity is shown as a percentage:
100% relative humidity means the air is holding as much water vapor as it possibly can (it’s “full”), and condensation may form.
50% relative humidity means the air is holding half of the water vapor it could hold at that temperature.
Why it Matters
Why it Matters
You can have the same amount of water vapor in the air on two different days but feel very different levels of humidity because of the air temperature. For example:
On a hot day, the air might not feel very humid even with lots of moisture, because warm air can hold much more water vapor.
On a cool day, the same amount of moisture might make the relative humidity high, making it feel damp or sticky.
Winter Air
Winter Air
Have you ever noticed that your skin gets itchy, your lips crack, or you get more static electricity in the winter? That “dry feeling” comes from the way cold air interacts with water vapor.
Air has a limit to how much water vapor it can hold, and that limit depends on temperature. Warm air can hold a lot of moisture, while cold air can hold very little.
When winter brings cold temperatures, the air naturally contains much less water vapor. Even if the relative humidity is high outside, the actual amount of moisture in cold air is still low.
When cold outside air enters your home, your furnace or heater warms it up. But heating the air doesn’t add any moisture—it simply raises the temperature.
Warmer air could hold more water vapor, but since no moisture was added, the relative humidity drops sharply, making the indoor air feel extremely dry.
Dry winter air leads to:
Dry skin and chapped lips
Scratchy throats and irritated sinuses
Static electricity (like shocks when touching metal)
Faster evaporation from your skin and surroundings
This is why many people have humidifiers running during the winter, to add moisture to the air and increase the humidity.
Sweating
Sweating
When your body starts to heat up, your brain sends signals to your sweat glands. These glands release sweat, which is mostly water with a little salt.
The key part isn’t the sweating itself—it’s what happens next: evaporation.
As sweat evaporates from your skin, it absorbs heat from your body and cools you down. This process is extremely effective, which is why sweating is one of the best cooling systems in the animal kingdom.
On a hot and humid day, sweating doesn’t cool you as well. Here’s why:
On a hot and humid day, sweating doesn’t cool you as well. Here’s why:
Humidity is the amount of water vapor already in the air.
When the air is very humid, it is almost full of water vapor.
This means sweat on your skin evaporates much more slowly—sometimes not at all.
If your sweat can’t evaporate, you’re still getting wet by sweating, but you’re not getting cooled. As a result:
You feel hotter than the actual temperature
Your body works harder to cool down
You can overheat more easily
Heat exhaustion or heat stroke becomes more likely
This is also why weather services report a “heat index”—how hot it feels when you combine temperature with humidity.
Dew Point Temperature
Dew Point Temperature
Have you ever walked outside early in the morning and seen water droplets on grass, cars, or spiderwebs? Those droplets formed because the air reached its dew point temperature.
The dew point is the temperature at which the air becomes completely full of water vapor—meaning it reaches 100% relative humidity. When the air cools to this temperature, it can’t hold any more moisture, so water begins to condense out of the air and form liquid droplets.
How Dew Point Works
How Dew Point Works
Warm air can hold a lot of water vapor.
As the air cools, it can hold less and less water vapor causing the relative humidity percentage to increase.
Example: 20% → 30% → 50%
If the air cools enough to reach the dew point (100% relative humidity), excess water vapor condenses and turns into liquid water.
Why Dew Point Matters
Why Dew Point Matters
When you want to know how humid or uncomfortable the air will feel, dew point is much more accurate than relative humidity.
Here’s why:
Relative humidity is a percentage that tells how full the air is compared to its maximum capacity at that temperature.
But this can be misleading:
50% relative humidity on a hot day can feel miserable.
50% relative humidity on a cold day can feel dry.
So the same percentage can feel completely different depending on the air temperature.
The dew point tells you how much actual moisture is in the air. Higher dew points mean there is more water vapor, no matter the temperature.
This makes dew point a better indicator of comfort and how it feels outside.
Quizlet
Report abuse