AP Physics 1 · Exam guide
AP Physics 1 Experimental Design Question Explained: How to Plan an Experiment and Use the Data
Every AP Physics 1 exam has an experimental design question. It describes a goal, such as measuring a spring constant, and asks you to plan an experiment that would reach it. The question rewards a clear, repeatable plan and a way of turning the data into an answer. The data below are made up for practice.
What graders look for
| Element | What a strong answer includes |
|---|---|
| Goal and relationship | The equation connecting the quantity you want to the ones you can measure. |
| Variables | What you change (independent), what you measure (dependent), and what you keep constant. |
| Equipment | Each item, with what it measures, such as a meterstick for length or a stopwatch for time. |
| Procedure | Steps another student could follow, including repeated trials. |
| Analysis | How you will use the data, usually a graph whose slope gives the quantity you want. |
A worked example: finding a spring constant
Goal: determine the spring constant k of a spring. The relationship is Hooke's law, \(F = kx\), where x is the stretch from the spring's relaxed length.
- Independent variable: the hanging mass, which sets the force \(F = mg\).
- Dependent variable: the stretch x of the spring.
- Constant: the same spring, and the same starting position of the ruler.
- Equipment: a stand, the spring, a set of known masses, and a meterstick.
- Procedure: hang each mass in turn, wait for it to settle, measure the stretch, and repeat each mass three times to find an average.
Made-up results, using g of 10 m/s\(^2\):
| Mass (kg) | Force F = mg (N) | Average stretch x (m) |
|---|---|---|
| 0.10 | 1.0 | 0.05 |
| 0.20 | 2.0 | 0.10 |
| 0.30 | 3.0 | 0.15 |
| 0.40 | 4.0 | 0.20 |
| 0.50 | 5.0 | 0.25 |
Graph F on the vertical axis against x on the horizontal axis. The points fall on a straight line through the origin, and the slope is the spring constant: \(k = \Delta F / \Delta x = (5.0 - 1.0) / (0.25 - 0.05) = 20\) N/m.
It names no measurements, no repeated trials and no way of finding k.
It names the variables, equipment, repeated trials and the analysis.
Common mistakes
- Describing what you would see without naming what you would measure.
- Leaving out a measuring device, such as the stopwatch or meterstick.
- Running only one trial, so one mistake spoils the result.
- Using an average of the data instead of a graph when the question asks how the data would be analyzed.
- Forgetting the units of the slope, which tell you what it means.
Frequently asked questions
What is the experimental design question?
A free-response question that asks you to plan an experiment for a stated goal, identify variables and equipment, and say how you would analyze the data.
Why do I graph the data?
A straight-line graph lets you find the quantity you want from the slope and checks that the relationship holds across all your data.
How many trials should I describe?
At least three at each setting, so you can average them and notice a bad measurement.
What if the graph would not be a straight line?
Choose what to plot so that it would be a line, such as plotting the square of a quantity against another.
Where can I find the official scoring rules?
Exam formats change a little from year to year, so check the current course and exam description on the College Board site before test day.
Keep practicing
Every lesson in the AP Physics 1 course ends with practice items and an Exam focus box, and every unit has a ten-question practice set with worked answers. These free lessons also build the skills the free-response section tests:
- Free lesson 1.3: representing motion with graphs
- Free lesson 1.4: the constant acceleration equations
See the AP Physics 1 course Free lessons and lesson list
Other free-response guides:
- AP Physics 1 FRQ Guide: Experimental Design, Translation and Written Arguments
- AP Physics 1 Qualitative/Quantitative Translation Explained: Connecting Equations and Explanations
- AP Physics 1 Paragraph Argument Explained: Writing a Claim, Evidence and Reasoning Answer
AP is a registered trademark of the College Board, which is not affiliated with and does not endorse this site. This guide is our own explanation of the question types and scoring. For the official scoring guidelines, see the College Board.