acceleration

Meaning: Acceleration is the rate at which velocity changes with time. Velocity is a vector, so an object accelerates when its speed changes, its direction changes, or both. By Newton's second law, the net force sets the acceleration, which points the same way as that force.

Equation: a = Δv/Δt = Fnet/m, where a is acceleration (m/s²), Δv is the change in velocity (m/s), Δt is the elapsed time (s), Fnet is the net force (N), and m is mass (kg).

On the MCAT: On a velocity-time graph, the slope is acceleration and the area under the curve is displacement. In projectile problems with no air resistance, horizontal acceleration is zero and vertical acceleration is g downward. In uniform circular motion, the centripetal acceleration v²/r points toward the center.

Common confusion: A negative acceleration does not mean slowing down; the sign only gives direction along the chosen axis. An object slows when its acceleration is opposite its velocity. Zero velocity also does not mean zero acceleration: a ball at the top of its flight still accelerates at g.