Circular Motion

Objective: Explain model limits and curved paths under gravity.

In ideal free fall near Earth, gravity alone produces approximately 9.8 m/s² downward acceleration regardless of object mass. Air resistance is a contact force that often grows with speed and depends on shape, area, and fluid conditions. When downward weight is balanced by upward drag, a falling object can reach approximately constant terminal speed. A satellite in orbit remains under gravity and is continually falling around Earth while its sideways motion prevents immediate surface impact in the idealized model. The orbital path and speed depend on gravity and initial conditions. “Weightless” in free fall commonly describes lack of support force, not absence of gravitational attraction.

Objective: Apply circular motion to calculations, evidence, and specified situations.

Uniform circular motion has constant speed but changing velocity direction. Its inward acceleration is a_c=v²/r, requiring inward net force mv²/r. “Centripetal force” names the net inward role of actual forces such as tension or gravity, not an additional new interaction. The period is circumference divided by speed. If an inward force disappears, the object initially travels tangent to the circle in an inertial frame. These relations assume the specified circular path and speed.