Lesson 21

Card 2.6: Conductivity and Corrosion

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Format: Experiment (multi-day observation)

Time: 30 min setup, checks over a week

Prerequisites: Card 2.1 helps

Core Question

Pool water is gentle. Seawater is a conductive, corrosive electrolyte that attacks every exposed joint. What does it actually do to our electricity and our metal?

Resource (~10 min)

Measure resistance between two probes in distilled water, tap water, and salt water. Watch conductivity climb with dissolved ions.
Two corrosion modes we care about: plain rust over time, and galvanic or electrolytic corrosion, which is rust with a battery behind it, shockingly fast.

Activity

Corrosion race: three jars of salt water. Jar A, a bare steel fastener. Jar B, two dissimilar metals touching (steel and copper). Jar C, two fasteners wired to a low-voltage supply. Photograph on day 0, then check and photograph at each class for a week. Write three observations and rank the jars by damage.

Clearing This Card

The photo log with observations, plus a 90-second oral check: “Why does a powered, exposed joint corrode fastest, and what two practices from Card 2.3 prevent it on our robot?”

If You Miss This Class

The jars run on their own schedule; photograph them during studio time and write the same log.

Why This Matters

This is the WHY behind every waterproofing rule in Unit 2, and conductivity itself shows up in mission sensor tasks. Corrosion is also the slow killer of vehicles that survive the season: this card is why we rinse.