Kinematics: Describing Motion

TL;DR

Kinematics is all about describing how things move without worrying about why they move. You'll learn about position, velocity, and acceleration to precisely track an object's path. We'll mainly focus on motion in a straight line, which is simpler but builds the foundation for more complex scenarios.

1. The Mental Model

Think of kinematics like giving directions: you're telling someone where something is, how fast it's going, and if it's speeding up or slowing down. You're not concerned with who's driving or what kind of engine it has, just the motion itself.

2. The Core Material

Kinematics is the foundational part of mechanics that deals with the description of motion without considering the forces that cause the motion. We use a few key quantities to describe motion precisely.

Position, Displacement, and Distance

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• Position is where an object is located relative to a reference point (origin). It's a vector, meaning it has both magnitude (how far) and direction. We often use $x$ for horizontal position and $y$ for vertical.
• Distance is the total path length traveled. It's a scalar, so it only has magnitude.
• Displacement is the change in an object's position. It's a vector, pointing from the initial position to the final position.
  • Displacement ($\Delta x$) = Final position ($x_f$) - Initial position ($x_i$)

Speed and Velocity

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• Speed is how fast an object is moving, regardless of direction. It's a scalar.
  • Average Speed = Total Distance / Total Time
• Velocity is how fast an object is moving and in what direction.