Free fall is motion in which gravity is the only force acting on an object, so every object accelerates downward at g (about 9.8 m/s² near Earth's surface) regardless of its mass, making it a constant-acceleration situation you can solve with kinematics equations.
Free fall means gravity is the only force in the picture. No air resistance, no normal force, no friction, nothing else. Draw the free-body diagram (LO 2.2.B) and you get exactly one arrow, the gravitational force, pointing toward the center of the Earth.
Here's the part that makes free fall so useful on the exam. Because the gravitational force on an object is mg and Newton's second law says a = F/m, the mass cancels. Every object in free fall accelerates at the same rate, g ≈ 9.8 m/s² near Earth's surface, whether it's a bowling ball or a feather (in a vacuum). That makes free fall a constant-acceleration problem, which means all the kinematics equations from Unit 1 apply directly. 'Free fall' also doesn't just mean falling straight down. An object thrown upward is in free fall the instant it leaves your hand, even while it's still rising, because gravity is the only force acting on it the whole flight.
Free fall is one of the most cross-cutting setups in AP Physics 1. It lives in Topic 1.2 (Representations of Motion), where you describe its velocity and acceleration over time (LO 1.2.B), in Topic 2.2 (The Gravitational Field), where the single-force free-body diagram comes from (LO 2.2.A and 2.2.B), in Topic 2.7, where Newton's second law explains why a = g for any mass, and in Topic 3.4, where g changes on different planets and free fall becomes a clean test case for conservation of mechanical energy (LO 3.4.B). If you can recognize 'gravity is the only force,' you immediately know the acceleration, the shape of every motion graph, and that mechanical energy is conserved. That one recognition unlocks three units' worth of tools.
Keep studying AP Physics 1 Unit 2
Acceleration due to Gravity (Units 1-3)
Free fall is the situation; g is the number that describes it. On a different planet, g changes (Topic 3.4), but the logic stays identical. An object in free fall on the Moon still has constant acceleration, just a smaller one.
Projectile Motion (Unit 1)
A projectile is just free fall with horizontal velocity. The vertical motion is plain free fall (constant acceleration g downward) while the horizontal velocity never changes because gravity has no horizontal component. Once you see projectiles as 2D free fall, the whole topic gets easier.
Kinematics Equations (Unit 1)
Free fall is constant-acceleration motion, which is exactly when the kinematics equations are valid. Plug in a = -g (with up as positive) and every free-fall problem becomes a standard kinematics problem.
Conservation of Mechanical Energy (Unit 3)
Gravity is a conservative force, so for an object-Earth system in free fall, mechanical energy is constant (LO 3.4.B). Kinetic energy and gravitational potential energy just trade back and forth, which gives you a second, often faster, way to find speeds without timing anything.
Free fall shows up everywhere on the exam without always being labeled 'free fall.' MCQs love graph questions (what do position, velocity, and acceleration vs. time look like for a ball thrown straight up?) and conceptual traps like 'what is the acceleration at the top of the flight?' (it's still g, not zero). FRQs use it as a building block. The 2019 FRQ 2, for example, compares a system's acceleration to that of an object in free fall to test whether you understand that free fall is the maximum acceleration gravity alone can produce; a hanging block connected to anything else accelerates at less than g. Be ready to draw the one-force free-body diagram, justify why acceleration is independent of mass using Newton's second law, sketch and interpret motion graphs, and switch to energy conservation when the question asks for speed at a height rather than time.
Free fall and terminal velocity are opposite ends of a falling story. In free fall, gravity is the only force, so the object keeps accelerating at g. At terminal velocity, air resistance has grown until it balances gravity, the net force is zero, and the object falls at constant speed. A skydiver at terminal velocity is technically not in free fall by the AP definition, because a second force (air drag) is acting. Quick check on any problem that says 'air resistance is negligible': that phrase is the exam telling you it's free fall.
Free fall means gravity is the only force acting on an object, so its free-body diagram has exactly one arrow pointing down.
All objects in free fall accelerate at g (about 9.8 m/s² near Earth) regardless of mass, because mass cancels in Newton's second law.
An object thrown upward is in free fall during its entire flight, including at the very top, where velocity is zero but acceleration is still g downward.
Free fall is constant-acceleration motion, so all the Unit 1 kinematics equations apply directly with a = g.
Because gravity is a conservative force, mechanical energy is conserved in free fall, letting you trade kinetic and potential energy to find speeds without using time.
Anything attached to other objects or fighting air resistance accelerates at less than g, which is why free fall sets the ceiling for gravity-driven acceleration.
Free fall is motion where gravity is the only force acting on an object. Near Earth's surface, that means a constant downward acceleration of about 9.8 m/s², no matter the object's mass.
No. At the peak, the ball's velocity is momentarily zero, but its acceleration is still 9.8 m/s² downward because gravity never stops acting. This is one of the most common misconception traps on the exam.
No. The gravitational force on a heavier object is larger (mg), but so is its inertia (m), so Newton's second law gives the same acceleration g for every object. Heavier things only fall faster in real life because of air resistance, which free fall problems ignore.
Free fall has gravity as the only force, so the object accelerates the whole time. Terminal velocity happens when air resistance grows to equal gravity, making the net force zero and the speed constant. If a problem includes air resistance, it's not free fall.
Yes, as long as air resistance is negligible. A projectile is just free fall with an initial horizontal velocity. Its vertical motion accelerates at g while its horizontal velocity stays constant.