lesson

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Imagine a camera drone tracking an athlete, flying diagonally across a field at 37∘ north of east at a speed of 10 m/s.
How do we figure out how fast it moves purely eastward versus purely northward?
To solve this, we resolve vectors into orthogonal Cartesian components — breaking two-dimensional motion into independent horizontal (x) and vertical (y) parts.
📊Interactive 2D vector decomposition diagram. Shows a 2D Cartesian grid with an origin (0,0). A vector arrow labeled v = 10 m/s points at 37 degrees above the positive x-axis. Dotted projection lines drop to the x-axis (highlighting vx = 8 m/s with unit vector i-hat) and y-axis (highlighting vy = 6 m/s with unit vector j-hat). Clean right-angle indicator at (8,0). Colors: #1e2945 text, #3b82f6 for x-component, #10b981 for y-component, #6366f1 for resultant vector.
How do we describe an object's position on a flat plane before it even starts moving?
Position and Displacement Vectors
A position vector r points directly from the origin (0,0) to the object's coordinates (x,y), written as r=xi^+yj^.
The symbols i^ and j^ are unit vectors — directional markers with a magnitude of exactly 1 pointing along the positive x and y axes.
When an object shifts from initial position r1 to final position r2, its displacement Δr is the straight-line difference Δr=r2−r1=(x2−x1)i^+(y2−y1)j^.
📊Vector subtraction diagram on a Cartesian plane. Shows r1 arrow from (0,0) to point P1(2, 3) and r2 arrow from (0,0) to point P2(7, 6). A bold displacement vector Delta r connects P1 to P2. Dashed horizontal and vertical legs show Delta x = 5 i-hat and Delta y = 3 j-hat forming a right triangle. Clear color-coded labels: r1 (light slate), r2 (purple), Delta r (navy blue #1e2945).
If we only know a vector's overall magnitude and launch angle, how do we split it into coordinates — and how do we rebuild it later?
Resolving and Reconstructing Vectors
In 1637, René Descartes introduced coordinate geometry to connect algebra and shapes, giving us the right-triangle tools we use to resolve vectors.