I overheard some of the conversation between the tutor and the tutee. That plus the mathematical symbols on the paper led me to conclude that I was witnessing a physics lesson.

I used the blind drawing technique to draw the contours of the heads. Usually, a complete blind drawing results in some dislocation of body parts. However, limited use of blind drawing led to a fairly realistic drawing (even though the proportions are a bit wrong).

Physics Lesson
Pen and Ink Sketch
10″x8″ 111# Moleskin Journal