الأسبوع 6 · الدرس الرابع «طرق انتقال الحرارة» (٢): الحمل ونسيم البحر والإشعاع والتصوير الحراري · 3 دروس
2
Sea breeze and the room heater
Science Prep 2 Term 1, Unit 1: pp. 35–38
GoalExplain how a sea breeze forms and name its direction by where the air comes from.
New words
sea breeze · wind that blows from the sea to the land in the daytimespecific heat · the heat needed to warm 1 kg of a substance by 1 °Cland · the solid ground, here sand and soil
Explanation
A sea breeze is convection on a big scale. On a sunny day, the land and the sea receive the same sunshine, but the land warms much faster, because soil and sand have a lower specific heat than water. The air above the hot land warms, expands and rises. Cooler air from over the sea moves in over the land to replace it, and we feel this as a breeze coming from the sea. High up, the air flows back towards the sea, sinks, and the loop is complete. The sea breeze blows harder in the hot months, because the land and the sea then differ more in temperature. At night the pattern reverses: the land cools quicker, so the breeze blows from land to sea. We always name a wind by where it comes from, so a wind blowing from the sea to the land is a sea wind.
Worked examples
On a summer afternoon in Alexandria, the sand is too hot to stand on, but the sea is much cooler. A breeze from the sea keeps the city cooler. The sand has a low specific heat, the sea a high one.
Which way does the breeze blow at midday near a coast: from land to sea or from sea to land? From the sea to the land, because the air over the land is rising and cooler sea air flows in.
Why is the sea breeze stronger in summer? The land becomes much hotter than the sea in summer, so the difference in temperature is larger and the air moves faster.
Class activity
Breeze model, with a grown-up. Place a bowl of sand and a bowl of water, same amounts, in the sun for 30 minutes. Read the temperature of the sand and of the water with a digital thermometer. Write what you notice. Then draw the loop of air for a coast at midday, using arrows and the words sea, land, warm air, cool air. Do not look at the Sun.
Practice
1
Why does land warm faster than the sea in the Sun?
Land has a lower specific heat than water.
2
In the daytime, which air rises: over the land or over the sea?
The air over the land.
3
Name a sea breeze by where it comes from.
It comes from the sea (blows from sea to land).
4
What would you expect at night, when the land cools faster than the sea?
The air moves the other way: a breeze from the land to the sea.
