Grade 7- The Earth

Size of the Earth

• Equatorial diameter-12756km

• Equatorial circumference- 40085km

• Polar diameter- 39995km

• Surface area of the earth- 510×106 km2

• Water surface – 73%

The shape of the earth

The shape of the earth is called geoid/ovoid/oblate spheroid due to being an imperfect sphere by being wide at the equator and flat at the poles.

The Position of the Earth in the Solar System

1. The 3rd planet from the sun

2. The earth and the heavenly bodies make the universe

3. The only planet that supports life

4. The home of man

5. Approximately 149m km from the sun

6. Takes 365 ¼ days to revolve around the sun

7. Has one satellite, the moon

Rotation of the Earth

1. Movement of the earth on its own axis (imaginary line through the centre from N pole to S pole

2. Rotates through 360º)

3. Takes 24 hours (day) to complete 1 rotation

4. Rotates in an anticlockwise direction (west to east)

Effects of Rotation of the Earth

1. Creates day and night because at any one time one side of the earth faces the sun (day) and the other remains in darkness (night).

2. Causes deflection of winds and ocean currents in the N hemisphere to the left and in the S hemisphere to the right.

3. It causes rising and falling of ocean tides.

4. Causes time difference between longitudes.

Effects of Rotation of the Earth on human activities

1. Effects of Rotation- How rotation affects human activities

2. Day and night- Planning Day and night activities

3. High and low tides- Helps in fishing activities Sea transport

4. Deflection of winds and ocean currents- Triggering of cyclones, hurricanes and tornadoes for example the

5. Deflection cause pressure changes which affect ocean currents and movement of wind Growing of crops Aviation or sea transport, Causes flooding

6. Time Difference- Travelling Education Sports

Revolution of the Earth

• Movement of the earth in its orbit around the sun.

• It’s in anticlockwise direction.

• The orbit of the earth’s revolution is elliptical.

• Takes 365 ¼ days in a year or 366 days in a leap year (every 4 years).

• The sun moves from the tropic of cancer to the equator and then towards tropic of Capricorn and back to the tropic of cancer.

• 21st march and 23rd September are called equinoxes because the length of day and night is equal. The sun is vertically overhead at noon at the equator.

• 21st June is called summer solstice because its summer in the N hemisphere. The sun is vertically overhead at noon at the tropic of cancer.

• 22nd December is called winter solstice because its winter in the S. hemisphere. The sun is vertically overhead at noon at noon at the tropic of Capricorn.

• Solstice is the period of maximum tilting of the earth towards the sun.
  

Effects of the Revolution of the earth

1. Causes the four seasons summer, autumn, winter and spring due to the movement of overhead sun causing changes in the heat belt.

2. Causes variation of day and night’s lengths due to the earth’s axis being inclined to the

3. path of revolution at an angle of 60◦.

4. Equinoxes have equal lengths of day and night.

5. Summers have longer days and shorter nights.

6. Winters have longer nights and shorter days.

7. Causes changes in the altitude of the midday sun due to the earth’s orbit being elliptical.

8. Highest altitude during equinox.

9. Lowest altitude during solstices.

10. Causes lunar eclipse due to revolution bringing the earth in line with the sun and the moon.

Effects of the Revolution of the earth on human activities

1. Changes in the position of midday sun at different times of the year

2. Varying length of day and night at different times of the day

3. Seasons