Gravitational fields

• What is a force field?

  An area with a non-contact force
• How can force fields be represented?

  As vectors and field line diagrams
• What does the distance between field lines indicate?

  The strength of the force exerted
• What forms force fields?

  Interactions of masses or charges
• What are the types of force fields?

  • Gravitational fields: interaction of masses
  • Electric fields: interaction of charges
• What are the similarities and differences between gravitational and electric forces?

  Similarities:

  • Both follow an inverse-square law
  • Use field lines for representation
  • Have equipotential surfaces

  
  

  Differences:

  • Gravitational force is always attractive
  • Electric force can be repulsive or attractive
  • Electric force acts on charge, gravitational on mass
• What does gravity act on?

  Any objects with mass
• What does Newton's law of gravitation state?

  Gravitational force is proportional to mass product
• What is the formula for gravitational force?

  $F =$$\frac{G m_1 m_2}{r^2}$
• What are the two types of gravitational fields?

  Uniform field and radial field
• How does a uniform field behave?

  Exerts the same force everywhere
• What happens to force in a radial field as distance increases?

  The magnitude of the force decreases
• What is gravitational field strength (g)?

  Force per unit mass in a field
• How does gravitational field strength vary in different fields?

  Constant in uniform, varies in radial
• What is the formula for gravitational field strength in radial fields?

  $g =$$\frac{GM}{r^2}$
• What is gravitational potential (V)?

  Work done per unit mass against gravity
• What is the gravitational potential at infinity?

  Zero
• How does gravitational potential change as an object moves from infinity?

  It becomes negative as energy is released
• What is the formula for gravitational potential in a radial field?

  $V =$$-\frac{GM}{r}$
• What is gravitational potential difference?

  Energy needed to move unit mass between points
• What are equipotential surfaces?

  Surfaces of equal gravitational potential
• What happens when moving along an equipotential surface?

  No work is done
• How is gravitational potential related to distance?

  Inversely proportional to distance
• How can you measure gravitational field strength from a graph?

  By calculating the gradient of the tangent
• What does the area under a graph of gravitational field strength represent?

  Gravitational potential difference
• What does Kepler's third law state about orbital period and radius?

  Orbital period squared is proportional to radius cubed
• What force acts on an object in circular orbit?

  Gravitational force acts as centripetal force
• What is the formula for the total energy of an orbiting satellite?

  Total energy = kinetic + potential energy
• What is escape velocity?

  Minimum velocity to escape gravitational field
• What is the formula for escape velocity?

  $v =$$\sqrt{\frac{2GM}{r}}$
• What is a synchronous orbit?

  Orbital period equals rotational period of the object
• What is a geostationary satellite?

  Satellite with a 24-hour orbital period above the equator
• How do you find the orbital radius of a geostationary satellite?

  Using the derived relationship from Kepler's law
• What is the approximate altitude of a geostationary satellite?

  About 36,000 km above Earth's surface
• What are the characteristics of low-orbit satellites?

  • Lower orbits than geostationary satellites
  • Travel much faster
  • Smaller orbital periods
  • Require less powerful transmitters
  • Useful for weather monitoring and scientific observations
• Why do low-orbit satellites require many to cover a region?

  They travel quickly and have smaller orbital periods