Electrostatics: Building Reasoning Through Observation and Inference

The instructor pacing guide suggests 15 minutes for introductions and new team assignments, 45 minutes to reach the charge diagram stage (Part I through Q6, including peer feedback), 30 minutes for oppositely charging tapes (through Q9), and 30 minutes for Part II challenges. Students reaching Part II is treated as a stretch goal — if they don't get there, that's fine.

The lab includes several instructor demonstrations that can be mixed in as students work: can roller (charged rod pulling an empty soda can), water bender (charged rod deflecting a thin water stream), half-charged rod on a rotating stand with T and B tapes, electroscope charging by contact and induction, electro-flyer (charged mylar hovering over a charged plastic loop), pith ball charging and repulsion, and "The Force" (bringing an uncharged hand near a charged rod on a pivot). Not all need to be performed; choose based on time and available equipment.

Electroscopes have two touchpoints (top and bottom) with removable disc or sphere attachments — have students examine the electrical connections to understand what contacts what. The needle assembly is delicate; caution students to touch gently if at all.

For students who miss the session, a makeup version can be completed at home using everyday materials (plastic plates, containers, utensils, different cloths, wax paper, plastic wrap, foil, balloons). They complete Part I at home and do the Demonstration option using online videos of electrostatic effects. 

This is Lab 4 in a 9-lab introductory physics sequence. It follows three circuits labs in which students build the circuit model (there is a flow of charges; more resistance reduces flow; more paths increase flow). This lab pivots from circuits to electrostatics, and the opening slides explicitly bridge the two: "Your electrical explorations so far" presents the circuit model alongside the electrostatic model introduced in lecture. Students should already know from lecture that there are two types of charge (positive and negative) and that like charges repel while opposite charges attract.

Following this lab, students complete two magnets labs (Labs 5–6), then transition to self-directed investigation labs (Labs 7–8) in which they formulate their own research questions, and conclude with a presentation lab (Lab 9). This lab also introduces the observation-versus-inference distinction and the practice of proposing multiple alternative explanations — reasoning habits that carry forward into the magnets labs and the self-directed investigations. Week 4 is also when new lab teams are assigned and midcourse feedback is collected.