The sine wave is a spinning circle

Why is AC a wave? Because it's really a circle! 🔄〰️

1️⃣ SPIN AN ARROW: an arrow of length 1 turns around a circle. Plot its height against the angle and you get a sine wave: sin 0° = 0, sin 90° = 1, sin 180° = 0, sin 270° = −1. One full turn (360°) = one wave.

2️⃣ THAT'S YOUR MAINS: make the arrow 325 V and spin it 50 times a second (a 2-pole generator turns at 3000 rpm). One turn = one cycle, so 50 turns a second = 50 Hz, and the 325 V peak is the 230 V RMS on your socket.

3️⃣ PYTHAGORAS INSIDE: freeze the arrow at 30°. It's the long side (1) of a right triangle with height sin 30° = 0.5 and width cos 30° ≈ 0.866. 0.5² + 0.866² = 0.25 + 0.75 = 1. That's why sin² + cos² = 1 for every angle.

📌 Sine = the height of a spinning arrow.