Evaporation
6 Minutes
Evaporation for kids: learn how liquids turn into gas without boiling and the factors affecting it. An English science lesson.
- Difference between boiling at 100 degrees Celsius and evaporation
- How sunlight gives surface water molecules kinetic energy to escape
- Four factors affecting evaporation: wind, heat, humidity, and area
What this lesson teaches
Evaporation is the process in which a liquid turns into a gas without boiling. While water boils and turns into vapor quickly at its boiling point of 100 degrees Celsius from all sides, evaporation takes place slowly and only at the liquid surface.
How molecules evaporate
Water is made up of water molecules that are held together by an attractive force. These molecules constantly move and push against each other using kinetic energy gained from surrounding heat. Under normal conditions, the energy from surrounding heat is too low for molecules to break free from this attraction. When sunlight falls directly on the surface, the top molecules absorb heat energy, increasing their kinetic energy enough to escape into the air layer by layer.
Difference between boiling and evaporation
- Boiling happens when a liquid is heated to its boiling point temperature, such as 100 degrees Celsius for water.
- Boiling occurs equally from all sides of the water, making the liquid turn into gas very quickly.
- Evaporation happens without reaching the boiling point and occurs only at the surface.
- Evaporation is much slower because the liquid must turn into vapor one layer at a time.
Four factors that affect evaporation
- Wind: Higher wind speeds hitting a wet surface remove moisture and dry it faster.
- Heat: Strong heat from the sun increases the kinetic energy of water molecules so they escape more easily.
- Humidity: Lower humidity in the surrounding air allows water to evaporate at a quicker rate.
- Surface area: A larger surface area spreads water into thinner layers, allowing heat to evaporate each layer much faster than in folded cloth.
Evaporation in everyday life
A wet shirt dries quickly on a moving bike because strong wind, high summer heat, low humidity, and a large spread-out surface area work together. If the same wet shirt were folded up, the thick layers of water would take much longer to dry, which is why washed clothes are spread out on terraces. On a larger scale, evaporation causes lakes and ponds to dry up during hot summer weather. This process also drives the water cycle, where seawater evaporates into the sky and returns as rain.