UNIT: MEASUREMENT

ACT-Based Science: Precision, Accuracy & Experimental Error
OBJECTIVE:

This activity helps students understand the difference between precision and accuracy in scientific measurements. By using rulers, tape measures, and digital calipers, students will compare measurement tools, analyze discrepancies, and evaluate sources of experimental error. This hands-on approach strengthens critical thinking, data interpretation, and problem-solving skills, preparing students for ACT Science questions that require analyzing and interpreting data trends.

Materials Needed:

Ruler, tape measure, digital caliper

Small wooden block (or any flat object)

Recording sheet for measurements

STUDENT DIRECTIONS:

Goal:

In this hands-on activity, you’ll explore the difference between precision and accuracy in scientific measurements. You'll use three different tools to measure the same object, analyze your results, and evaluate possible sources of error. This activity builds the data interpretation, graphing, and critical thinking skills needed to succeed on the ACT Science section and in real-world science and engineering.

Step 1: Set Up Your Experiment

Collect your measurement tools and wooden block.

On your recording sheet, create a table with rows labeled for each tool (ruler, tape measure, caliper) and columns for Trial 1, Trial 2, Trial 3, and Average Measurement.

Step 2: Take and Record Measurements

Use the ruler to measure the length of the block three times. Write down each value.

Repeat the process using the tape measure and then the digital caliper.

Calculate and record the average measurement for each tool.

Step 3: Analyze Precision

Look at the three trials for each tool:

Are they close together? If yes, the tool has high precision.

Are they far apart? If yes, the tool has low precision.

Record your conclusion on which tool was most precise and explain why.

Step 4: Evaluate Accuracy Using Percent Error

Use the provided reference value (e.g., 10.5 cm) for the block’s true length.

Calculate percent error for each tool using the formula:

Record the percent error for each tool on your sheet.

Rank the tools from most accurate to least accurate based on percent error.

Step 5: Graph and Visualize the Data

Create a bar graph that compares the average measurements from all three tools.

Use a second graph (line or bar) to compare the percent error of each tool.

Add labels and titles to clearly show your findings.

Step 6: Application & Analysis

Answer the following questions on your worksheet or in a group discussion:

Why is it important to use precise and accurate measurements in scientific experiments?

How did the design of each tool impact the results?

What might have caused differences between the three trials? (e.g., human error, tool resolution)

What strategies can you use to reduce experimental error in future measurements?

Application & Analysis Questions

Why is it important to use precise and accurate measurements in scientific experiments?

How do different measurement tools affect the accuracy of collected data?

What factors contribute to experimental error, and how can they be minimized?

SCIENCE Thinking Challenge:

A student measures a block as 10.2 cm using a ruler but the actual length is 10.5 cm. What is the percent error? (ACT Science Score: 20-23)

1.2%

2.9%

3.5%

5.1%

A student uses a digital caliper and a ruler to measure the same object but gets different results. What is the most likely cause? (ACT Science Score: 24-27)

The ruler is always more accurate.

The caliper measures more precisely than the ruler.

The ruler has a lower resolution.

The caliper is likely broken.