5.4 Gravitational fields

avatar
Created by
Jainisha

Cards (14)

  • Gravitational field strength decreases as distance from the centre of mass increases
  • Gravitational field lines form a radial pattern around a point mass
  • Gravitational field strength per unit mass on a small object placed at that point
  • Gravitational field strength is a vector quantity but is always attractive, hence a negative value
  • Gravitational field lines show the direction and strength of the force faced by an object in that field
    The spacing of the arrows show the strength of the field
  • In a uniform gravitational field, gravitational field strength does not change - close to the surface of a planet
  • Newton's law of gravitation
    The force between two point masses is directly proportional to the product of masses and inversely proportional to the square of their separation
  • F=F=−GMmr2-\frac{GMm}{r^2}
    F - force
    G - gravitational constant, 6.67 ×10−116.67\ \times10^{-11}
    Mm - product of masses
    r - distance between centres of mass
  • g =g\ = Fm=\ \frac{F}{m}=−GMr2-\frac{GM}{r^2}
    g - gravitational field strength
    F - force
    M - mass of object causing the field
    m - mass of object in the field
    r - distance from the centre of mass
  • The negative sign in the gravitational field strength equation means that the field strength is in the opposite direction to the displacement
  • Kepler's first law
    The orbit of a planet is an ellipse with a sun at one of the two foci
  • Kepler's second law
    A line segment joining a planet and the sun sweeps out equal areas during equal intervals of time
  • Kepler's second law explains that as a planet is closer to the sun, it moves at a greater speed to cover the same area as it would if it were further from the sun
  • Kepler's third law
    The square of the orbital period (T) of a planet is directly proportional to the cube of its average distance from the sun
    T2∝r3T^2\propto r^3