Page 29 - Geography for Secondary Schools Student’s Book Form One

Geography for Secondary Schools
Student’s Book Form One
(iii) Gain or loss of a day

This effect is primarily related to crossing the International Date Line. One will lose a
day when crossing the International Date Line (IDL) from the East to the West, and will
gain a day when crossing the IDL from the West to the East. International Date Line is
an imaginary line that runs from the North Pole to the South Pole. It follows Meridian
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180° except where it crosses land surfaces to avoid confusion. If the Earth would not
be rotating, there would be neither gaining nor losing of a day while crossing the IDL.

(iv) Deflection of winds and ocean currents
The earth’s rotation causes deflection of planetary winds and ocean currents. This means
that they do not blow and flow straight. The planetary winds and ocean currents are
deflected to the right in the northern hemisphere and to the left in the southern hemisphere
(Figures 3.3a and b). This is based on Ferrel’s Law, which states that ‘‘freely moving
bodies are deflected to their right in the northern hemisphere and to their left in the
southern hemisphere from their point of origin’’.

Polar Easterlies
60°N

Westerlies

30°N
Trade winds

Equator Doldrums

Trade winds

30°S
Westerlies

60°S
Polar Easterlies

Figure 3.3 (a): Deflection of winds due to the earth’s rotation

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