Physics Experiments, Models, and Data

A good experiment makes its comparison visible. It names what changes, what is measured, what stays controlled, and how uncertainty limits the conclusion.

This lesson supports Chapter 26 of Physics for Beginners. Keep the physical picture in view, write the units, and check the direction of every vector before trusting a calculation.

Turn a broad idea into a testable question

The independent variable is changed deliberately. The dependent variable is measured in response. Controlled variables are kept as consistent as practical. A control condition supplies a reference when the design needs one. Repeated trials reveal scatter, but repetition cannot repair a miscalibrated instrument.

Report what the instrument can support

A measurement needs a value, unit, and justified precision. Accuracy describes closeness to an accepted value, while precision describes repeatability or resolution. Random uncertainty creates scatter. Systematic error shifts results in a consistent direction.

Let graphs test the model

Choose axes that match the independent and dependent variables. A best-fit line represents the overall trend rather than connecting every point. Slope has units and physical meaning. Residuals, the differences between observations and model predictions, can reveal curvature or another missed pattern.

Worked example

A student tests how pendulum length affects period. Length is the independent variable, and period is the dependent variable. The same bob, small release angle, timing method, and location should be controlled. Timing ten cycles per trial reduces the relative effect of reaction time.

Watch the idea in action

Khan Academy gives a focused explanation of the chapter’s central idea. Pause before each calculation and predict the next step on paper.

Practice questions

1. What is an independent variable?
2. What is a dependent variable?
3. Why repeat trials?
4. What is the difference between accuracy and precision?
5. What does a graph’s slope need besides a number?
6. What can a pattern in residuals reveal?

Answers

1. The variable changed deliberately.
2. The measured response.
3. To estimate scatter and reduce uncertainty in the mean.
4. Accuracy is closeness to an accepted value, while precision is repeatability or resolution.
5. Units and a physical interpretation.
6. A missed trend or a poor model form.

Keep studying

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