Fog, Dew & Frost

Why it matters

Tiny drops of dew on the morning grass, a blanket of fog on a cold day, sparkling frost on a window. All of these are water in disguise!

Predict first

How do dew drops appear on grass early in the morning?

At night the ground cools, and water vapour in the air condenses on the cold grass to form dew. It is the same water vapour turning back into liquid.

• Water vapour in the air cools on the grass and turns into liquid drops — correct
• The grass squeezes water out of its leaves
• It rains a tiny bit every morning
• The grass makes the water by itself

What you do

Sort each one: is it liquid water in the air, or frozen (solid) water?

Check yourself

Dew forms when water vapour in the air does what on a cool surface at night?

Dew forms by condensation: water vapour in the air turns into tiny liquid drops when it touches a cool surface at night.

On a very cold night when the temperature drops below 0°C, dew turns into what?

When it is cold enough (below 0°C), the water vapour freezes directly onto surfaces as frost. Frost is really just frozen dew.

Dew, fog, frost and clouds all come from the same thing. What is it?

Dew, fog, mist, clouds and frost all come from water vapour in the air. Depending on the temperature, the vapour turns into liquid drops or solid ice.

• Condenses (turns from gas into liquid) — correct
• Evaporates (turns from liquid into gas)
• Freezes into a solid straight away
• Burns up in the air
• Frost, which is frozen dew — correct
• Rain
• Fog
• Steam
• Water vapour in the air — correct
• Dust blown up from the ground
• Smoke from fires
• Tiny bits of ice from space