Reading: Develop the model
State the claim
Near a massive spherical body, the same gravitational interaction accelerates both a dropped object and an ideal circularly orbiting object. For the circular orbit, sufficient tangential velocity and continuous inward gravity bend the path without surface contact. Orbit is not the absence of gravity; it is a type of free fall.
Use two independent calculations
An inverse-square ratio supports gravitational field weakening with distance: g at doubled radial distance is one quarter the original. A circular orbit speed and period calculation supports the claim that gravity supplies the centripetal acceleration. For a 400 km Earth-model orbit, g≈8.69 m/s² and period≈92.4 min. State constants and rounded units.
Respond to likely objections
Misconception one: astronauts float because gravity vanishes. Explain shared free fall and lack of ordinary support forces. Misconception two: orbital distance is measured only from the surface; explain r=R+h. Misconception three: outward 'centrifugal force' is an additional physical force in the Earth-centered inertial-frame diagram; draw only actual gravitational force as the radial net force.
Write limitations and plan an improved model
Perfect circles, Earth as a sphere, an isolated two-body system, no atmospheric drag and constant parameter μ are idealizations. A stronger model would consider elliptical orbits, perturbations or actual tracking observations. Today's open-book practice bank gives feedback and an 80% correction target, but it is not a secure, official midterm or final examination.