IB Physics

Notes

IB Physics SL – Gravitational Fields Exam Review 1. Core Definitions Gravitational Field Strength (g) Definition: Force per unit mass g = F / m Units: N kg⁻¹ or m s⁻² Newton’s Law of Universal Gravitation F = G m₁ m₂ / r² G = 6.67 × 10⁻¹¹ N m² kg⁻² Force is proportional to the product of the masses. Force is inversely proportional to the square of the distance. If distance doubles, force becomes 1/4. 2. Gravitational Field of a Planet Field Strength Outside a Spherical Planet g = GM / r² Depends on planet’s mass. Decreases with square of distance. Direction: toward the centre. At the Surface of a Planet g = GM / R² R = radius of planet. 3. Weight vs Mass Weight W = mg Depends on gravitational field. Unit: Newton (N). Mass Amount of matter. Does NOT change with location. Unit: kilogram (kg). 4. Circular Orbits Gravity provides centripetal force. Without gravity, there is no orbit. Satellites are constantly falling toward Earth. Fg = Fc 5. Apparent Weightlessness Gravity still acts in orbit. Astronauts are in free fall. Astronauts and spacecraft fall at the same rate. No normal reaction force → feel weightless. 6. Escape Speed Depends on the mass of the planet. De...