Earth's Measurements and Properties

• What shape is the Earth commonly described as?


  An oblate spheroid
• What does the term "spheroid" refer to?


  A shape that is somewhat like a sphere but not a perfect sphere
• What does the term "oblate" indicate about the Earth's shape?


  It means the Earth is flattened at the poles and bulging at the equator
• What are reference lines parallel to the equator called?


  Latitudes
• What do reference lines that extend from the North Pole to the South Pole represent?


  Longitudes
• How do longitudes appear on a Mercator map?


  As parallel lines extending from top to bottom
• What happens to a sphere when it deforms along the latitude?


  It becomes an oblate spheroid
• What is the significance of the term "oblate" in relation to the Earth's shape?


  It indicates that the deformation occurs along the latitude
• What is the shape of a spheroid that is deformed along the longitude?


  An oblong shape
• Who was the first person to estimate the Earth's circumference?

  Eratosthenes of Alexandria
• What method did Eratosthenes use to estimate the Earth's circumference?


  A combination of geometrical calculations and physical observations
• What observation did Eratosthenes make about a well in Syene?


  The bottom of the well was illuminated at noon during the summer solstice
• What angle did Eratosthenes measure in Alexandria during the summer solstice?

  7.2 degrees
• How far apart were Alexandria and Syene according to Eratosthenes' measurements?


  5000 stadia
• How did Eratosthenes calculate the Earth's circumference?


  By using the formula $C =$$\frac{5000 \text{ stadia} \times 360}{7.2}$
• What was the calculated circumference of the Earth by Eratosthenes?


  250,000 stadia
• What is the numerical equivalent of a stadion in meters?


  157 meters
• What is the Earth's circumference in meters based on Eratosthenes' calculation?


  $39,250,000 \text{ meters}$
• What is the Earth's circumference in kilometers?


  Approximately 40,000 km
• What is the equatorial circumference of the Earth?


  About 40,075 km
• What is the polar circumference of the Earth?


  About 40,008 km
• What does Newton's Law of Universal Gravitation state?

  • Every object attracts every other object with gravitational force
  • Gravitational force is directly proportional to the product of their masses
  • Gravitational force is inversely proportional to the square of the separation between their centers
• What is the formula for gravitational force according to Newton's Law?


  $F_{grav} =$$\frac{G m_1 m_2}{d^2}$
• What is the value of the universal gravitational constant \(G\)?


  $6.67 \times 10^{-11} \text{ Nm}^2/\text{kg}^2$
• What does the variable \(g\) represent in the gravitational force equation?


  Acceleration due to gravity
• How can the Earth's volume be calculated?


  • Use the formula for the volume of a sphere:

  $V =$$\frac{4}{3} \pi r^3$

  • Where \(r\) is the Earth's radius
• How can the Earth's density be calculated?


  • Density \( \rho \) is calculated by dividing the Earth's mass by its volume:

  $\rho =$$\frac{m}{V}$
• How can the Earth's rotational speed be calculated?


  • Divide the distance traveled in one day by the time it takes to complete a sidereal day (23.93 hours)
• What is the formula for calculating the Earth's orbital speed around the sun?


  $s =$$\frac{2 \pi r_E}{t}$
• What is the average distance between the Sun and the Earth?


  149,597,870 kilometers (1 AU)
• What is the significance of star trails in relation to Earth's movement?


  • They show the apparent movement of stars in the night sky
  • Caused by the Earth's rotation
• What calculations should be shown for the Earth's mass, volume, and density?

  • Calculate Earth's mass using gravitational force equation
  • Calculate Earth's volume using the sphere volume formula
  • Calculate Earth's density using the density formula