The experimental method part of your lab report lets your audience know what you did to gather the data. Some professors call this the experimental procedure or just the procedure. What ever you call it, let’s take a look at how you can to write an effective one.

I’ll be using an example of a simple Hooke’s Law lab where we stretched a spring using different masses. The force and displacement were then compared. For some of my courses, the Hooke’s Law lab has multiple parts. In those courses, the examples here might be one section of a larger lab.

The experimental method may be a separate section in the lab report, or it may be a subsection of your introduction section. Make sure to check with your instructor to place it in the right spot. Regardless of where this information goes, there are some key things to consider.

Experimental Method Section vs. The Lab Handout

The experimental method section of your lab is not meant to be a step-by-step instruction manual for someone else to follow.  Many times I see that students copy and paste the instructions for the lab directly from the lab handout.

This is problematic for at least two reasons…

The first is that you are likely guilty of plagiarism while doing this.  When you directly copy a large part of someone else’s work, even when citing it, your professor can be consider it plagiarism.  Don’t do that.

The second reason is level related. “Real” scientific papers are not written as instruction manuals. In introductory college classes, we are transitioning from basic lab reports to professional-level writing. 

In “real” scientific papers, you share information about the general idea of what you did, along with specifics on some details. Your lab notebook will have all of the details, but the paper or lab report doesn’t.

The experimental method section is a description, not a recipe.

A chalkboard with ipsum lorem words. The first part is a list of numbered steps that is crossed out with a large x. The second section is a set of paragraphs with a green check mark.

Writing Style

Write your experimental method in a conversational method. Start from the idea of telling someone what you did in the lab today. Expand on that idea to include a few more details, which I’ll cover in a moment.  

We write this section in the past tense. You performed the experiment in the past.

Different professors and different journals will require different writing styles.  For my class, it is safe to say things in the active first-person voice:  “I measured” or “We prepared” are acceptable.  Some folks prefer passive voice, if you have been trained to use this, it is okay. “The mass was measured” is an example of the passive voice.

Make sure that you are using scientific language here. If someone is reading your paper, they are expecting you to talk science. For example, say that your spring oscillated, not bounced around.

How Long is the Experimental Method

The experimental method section of your lab report should be a few paragraphs long at most.  If your experiment had several parts, write a few paragraphs for each part.

Write enough to describe what you did in the lab, but not much more. It is okay to be a bit general, but if there are particular steps that were complex, go ahead and expand on them a bit.

What We Include

The experimental method should describe the general outline of what you did in the experiment.

Describe the Equipment

To start, describe the equipment that you used and how you set it up. Include the manufacturer of any specialized equipment that you used. Include your setup sketch and refer to it as necessary.

For this experiment, a spring was hung from a sturdy support. Metal nuts were then added to the spring.

Describe the Measurements

Next, talk about the measurements that you made. Explain details about how you made the measurement, and how many times you repeated each measurement. 

The bottom of the spring was measured before any mass was added. To make later calculations easier, I placed the ruler such that the bottom of the spring was at 0.0 cm. Large nuts with individual masses of 48.48 grams and small nuts with individual masses of 31.99 g were used. As more mass was added, the displacement of the spring after motion stopped was measured. The number of nuts and the resulting displacement were recorded. This was repeated in various combinations from a single nut to a total of 5 large nuts and two small nuts.

Briefly Describe Your Analysis

Now explain in general terms what you did with the measurements. You’ll give the details in your experimental results section.

Once the data was gathered, we determined the mass added and converted the masses from grams to kilograms. This mass was used to determine the force of gravity provided by the nuts. A graph of the data of force and resulting displacement was plotted. The slope of this graph was used to determine the spring constant.

As with the other parts of your lab report, make sure that you read and review your experimental method section before submitting it.  If you worked with a partner, you should each write your own lab report. Compare your experimental method section to make sure that neither of you missed anything important.