Stretchy Objects: Discovering When Hooke's Law Applies and When It Fails

Pacing. The instructor guide suggests: 10 min critiquing research questions, 5 min introducing Hooke's Law, 30 min on a pilot experiment with rough analysis, 30 min on an improved or extended experiment, and 30 min on results and conclusions. The two-phase experiment structure (pilot then improved) is important — it gives students explicit permission to scrap and restart, which many won't do without that signal.

Materials. Provide a variety of springs and have students also bring everyday stretchy objects (rubber bands, hair ties, elastic fabric, bungee cords). Remind them the week before. Have electronic force probes and sets of known masses available so groups can choose their measurement method. Warn students not to overstretch springs.

Graphing. A Desmos template with built-in uncertainty bars and multi-option trendlines is available and saves significant time. Point students to it early so they can plot as they go, which reinforces the iterative design cycle.

Research question critique. Use real student-proposed questions from the previous week's follow-up. Sorting them by common concern (too vague, already known answer, not feasible) makes the critique more efficient than reviewing them one at a time.

Makeup option. Students who miss this lab can analyze data collected by one of the attending groups, preserving the analysis and argumentation goals even without the hands-on design experience.

This is Lab 6 of 9 in an introductory physics lab sequence. It serves as a pivotal bridge between guided and independent work.

What comes before. Labs 1–3 (Pendulum) build foundational skills in measurement, uncertainty quantification, comparing data distributions, and interpreting t-scores. Labs 4–5 (Tossed Objects) introduce scientific integrity, bias mitigation, and sharing findings through short presentations. By Lab 6, students have practiced these skills in structured contexts and are ready to make most experimental decisions themselves.

What this lab does. It is the first time students design and execute a complete experiment from question to conclusion in a single session. It also formally introduces criteria for good research questions (answerable, experimental, feasible, focused, generalizable), which students then apply to critique peer-proposed questions.

What comes after. Labs 7–8 are a multi-week independent investigation in which each group pursues their own research question — the question-writing skills practiced in Lab 6 feed directly into this. Lab 9 is a final presentation. Lab 6 is thus designed as the transition point: the last instructor-defined topic and the launching pad for student-driven inquiry.

Prerequisite knowledge. Students should be comfortable with basic uncertainty estimation, graphing with error bars, and the concept of comparing data to a model. No prior knowledge of Hooke's Law is assumed — it is introduced during the session.