GoalShow that warm air expands and rises while cooler, denser air takes its place, and link this to winds at the coast.
New words
expand · to take up more spacesea breeze · wind that blows from the sea to the land during the dayair current · a stream of moving air
Explanation
When air is warmed, its particles move faster and spread out. The air expands and becomes less dense, so it rises. Cooler, denser air moves in underneath to take its place, and the result is an air current. A grown-up can show this with a paper spiral hanging on a thread. Over a warm radiator the spiral slowly turns, because the rising warm air pushes on it. Over a cool place it does not turn. Now link it to the coast. In the daytime the land warms faster than the sea. The air above the land rises and cooler air from the sea flows in to replace it: that is a sea breeze, a cool wind that comes in from the sea on warm days.
land warms faster→air above land rises→cooler sea air flows in→sea breeze
Worked examples
Place
Spiral turns?
above a warm radiator
yes, slowly
above a cool shelf
no
Seif hangs a paper spiral from a thread. A grown-up holds it above a warm radiator at a safe height. The spiral turns slowly. Over a cool shelf it does not.
In the afternoon on Alexandria’s corniche, Hana feels a cool wind from the sea. The land is hot and its warm air is rising.
Youssef asks: does warm air rise because it is lighter than the same amount of cool air? Yes. Warm air is less dense.
Class activity
Spiral test. With a grown-up, cut a paper spiral and hang it on a thread. The grown-up holds it high above a warm radiator or heater, never near a hot bulb, flame or hot surface, and then over a cool place. Watch and compare. Draw arrows for the moving air.
Practice
1
What happens to air when it is warmed?
It expands, becomes less dense and rises.
2
What takes the place of the rising warm air?
Cooler, denser air.
3
What is a sea breeze?
A wind that blows from the sea to the land in the daytime.
4
Why does the paper spiral turn above a warm radiator?
