Gravitation: SPI Physics

Formulas (3)

• Newton's law of gravitation · Universal law of gravitation
  $$F = \frac{G m_1 m_2}{r^2} \qquad G = 6.67 \times 10^{-11}\ \text{N m}^2\,\text{kg}^{-2}$$
• The value of g and how it changes over the Earth · Acceleration due to gravity
  $$g = \frac{GM}{R^2} \approx 9.8\ \text{m/s}^2 \qquad W = mg$$
• Satellites and escape velocity · Escape velocity
  $$v_e = \sqrt{2gR} \approx 11.2\ \text{km/s} = 11200\ \text{m/s} \text{ for the Earth}$$

Watch out for (7)

• Halving the force when the distance doubles
  → Newton's law of gravitation
• Forgetting to square the distance
  → Newton's law of gravitation
• Putting the largest g at the equator
  → The value of g and how it changes over the Earth
• Giving a reason that has nothing to do with gravity
  → The value of g and how it changes over the Earth
• Saying mass changes on the Moon
  → The value of g and how it changes over the Earth
• Reading 11.2 as m/s
  → Satellites and escape velocity
• Matching a geostationary satellite to a year
  → Satellites and escape velocity