Gravitational Field Strength in a Radial Field

• What does gravitational field strength describe at a point?

  How strong or weak a gravitational field is
• What is the equation for gravitational field strength due to a point mass?

  g = $\frac{GM}{r^2}$
• What does the variable 'g' represent in the equation?

  Gravitational field strength (N kg$^{-1}$)
• What does the variable 'G' represent in the equation?

  Newton’s gravitational constant
• What does the variable 'M' represent in the equation?

  Mass of the body producing the field (kg)
• What does the variable 'r' represent in the equation?

  Distance between point source and position (m)
• What type of quantity is gravitational field strength, g?

  It is a vector quantity
• In which direction does gravitational field strength act?

  Towards the center of the body creating it
• What is the constant value of g on the Earth's surface?

  9.81 N kg$^{-1}$
• How does g behave outside the Earth's surface?

  g is not constant and decreases
• How does g change as r increases?

  g decreases by a factor of 1/r
• What type of relationship does g have with distance?

  It follows an inverse square law relationship

  
• What happens to g when r is less than R?

  g is directly proportional to r
• What happens to g when r is greater than R?

  g is inversely proportional to r
• What shape does the graph of g against r take when r > R?

  An 'L' shaped curve
• What is another term for g?

  Acceleration due to gravity
• What are the units for acceleration due to gravity?

  m s$^{-2}$
• What is the acceleration of an object falling freely in a uniform gravitational field on Earth?

  9.81 m s$^{-2}$
• How does the gravitational field strength on the Moon compare to Earth?

  • Moon's mean density is 3/5 of Earth's
  • Gravitational field strength on Moon is 1/6 of Earth's

  
• How do you determine the ratio of the Moon's radius to the Earth's radius?

  Using gravitational field strength and density

  
• From where is 'r' always taken in gravitational calculations?

  From the center of mass of the object
• Why is it important to draw the inverse square law graph of g against r?

  It is a common exam question
• What are the key features of the gravitational field strength graph?

  • g decreases rapidly with increasing distance r
  • g is directly proportional to r when r < R
  • g is inversely proportional to r when r > R