Introduction
Kinematics is the branch of physics that describes motion without considering the forces that cause it. It focuses on how objects move, not why they move. In AP Physics 1, kinematics is used to describe everyday motion such as cars accelerating, objects falling, or projectiles being launched. The main goal is to relate an object’s position, velocity, and acceleration over time using words, graphs, and equations. Motion is described relative to a chosen reference point and direction, making sign conventions extremely important. The fundamental quantities in kinematics are position, displacement, velocity, and acceleration. Displacement is the change in position and is a vector, meaning it has both magnitude and direction, unlike distance which is a scalar. Velocity describes how fast and in what direction an object’s position changes, while acceleration describes how velocity changes over time. Acceleration can occur even if speed is constant, as long as direction changes. In many AP Physics 1 problems, acceleration is assumed to be constant, which allows motion to be described using a small set of kinematic equations. For one-dimensional motion with constant acceleration, four core equations connect position, velocity, acceleration, and time. These equations allow you to solve for unknown quantities as long as three of the five variables are known. Special cases include motion at constant velocity (zero acceleration) and free fall, where the acceleration is the constant gravitational acceleration 𝑔 g. Correct use of signs and units is essential, and different equations are chosen depending on which variables are known or unknown. Two-dimensional motion, such as projectile motion, is handled by breaking vectors into horizontal and vertical components. The key idea is that horizontal and vertical motions are independent of each other except for sharing the same time variable. Horizontally, a projectile moves at constant velocity, while vertically it accelerates downward due to gravity. By analyzing each direction separately using the one-dimensional equations, quantities such as time of flight, maximum height, and range can be determined. Kinematics problems are often solved using graphs as well as equations. On a position–time graph, slope represents velocity, while curvature indicates acceleration. On a velocity–time graph, slope represents acceleration and area under the curve represents displacement. A strong understanding of these graphical relationships, combined with careful problem-solving steps and attention to common pitfalls (such as confusing distance with displacement or speed with velocity), allows kinematics to serve as the foundation for all later topics in mechanics..
Summary of Kinematic Equations
2. x = x₀ + v₀·t + ½·a·t²
3. v² = v₀² + 2·a·(x - x₀)
4. x = ½·(v + v₀)·t
These four equations describe motion under constant acceleration and allow you to predict position, velocity, or time based on known variables.
Other Resources
- Organic Chemistry Tutor — Intro to Kinematics
- Organic Chemistry Tutor — Kinematic Equations
- Walter Lewin Lecture Series
- Walter Lewin — 1D Kinematics
- Flipping Physics — Review Video
- Practice Problems (CrackAP)
- Khan Academy: AP Physics 1 Kinematics
- Learn AP Physics — Kinematics