# Day 12: Spring Lab

*College-Prep Physics:* We’ve been discussing the ball-and-spring model for solids, so now it’s time to investigate spring behavior in more detail. What is the relationship between the force applied to a spring and the amount the spring stretches? We’re keeping it simple: using spring scales to measure force and making stretch the independent variable. Each lab group takes data for two different springs.

(Concept check: Which pulls harder — the spring on the scale or the scale on the spring? What is the scale actually measuring?)

Lab technique/concepts to focus on:

- graphing by hand
- zeroing the spring scale while it’s horizontal, not vertical
- measuring stretch (subtraction method vs. direct method)
- 5 to 10 levels of the independent variable
- Multiple trials for each level of the independent variable.
- Wide range of values for the levels of the independent variables.
- HOW TO SPACE THEM OUT? Limiting factors:
- Maximum safe stretch = limitation of apparatus, can’t overextend. So if your spring can safely stretch to 50 cm, you maximum level will be 50 cm. Space your lower levels accordingly.
- Maximum force reading = limitation of instrument, can’t go beyond 5 N. Your spring may safely stretch out to 50 cm, but perhaps doing so means the force is larger than 5 N. So your maximum level will be the stretch at 5 N. Space your lower levels accordingly.

- HOW TO SPACE THEM OUT? Limiting factors:

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