Substitute Lesson Plan: Physics Lab — Measurement, Precision, and Accuracy

Objective

Students will be able to:

• Explain the difference between accuracy (how close a measurement is to the correct value) and precision (the spread/consistency of repeated measurements).
• Describe the displacement method for measuring the volume of an oddly shaped object.
• Correctly identify significant figures in a measurement, including rules for zeros as placeholders.

Materials

• High School Physics Lab Manual – Student Edition, Lab 1: "Measurement, Precision, and Accuracy" (Activity 1: Measuring Volume)
• Copies of Lab 1 pages for each student (or shared manuals)
• Paper and pencil for notes and exit ticket
• (If available per teacher's normal classroom setup) graduated cylinders, water, and small objects for the displacement method — otherwise this activity can be done as a reading/discussion exercise if no lab equipment is available for a substitute to safely supervise

Warm-up (~5 min)

1. Write on the board: "Accuracy vs. Precision"
2. Ask students to silently read the second paragraph of the Lab 1 introduction (the string measurement example, 30.48 cm).
3. Cold-call 2–3 students to explain in their own words: What does it mean for a measurement to be accurate? What does it mean for it to be precise?

Main Activity (~25 min)

1. (5 min) Have students read the "In this lab you will learn" section together as a class (aloud or silently), so they know the three learning goals: measuring volume by displacement, measuring mass with different tools, and measuring distance with rulers/meter sticks/string.
2. (10 min) Direct students to read the full text of Activity 1: Measuring Volume. As they read, have them answer these questions in their notes:
3. What is volume, according to the manual?
4. What is the displacement method, and when is it especially useful?
5. What are the three masses being measured with a graduated cylinder in this activity?
6. (10 min) Focus on significant figures. Have students reread the paragraph on significant figures and, in pairs, answer:
7. What counts as a "known digit" vs. the "doubtful digit"?
8. Are nonzero digits always significant?
9. When are zeros significant (give the example from the text: zeros surrounded by nonzero digits)?
10. When are zeros NOT significant (give the example from the text: zeros to the right, as in 1000)?
11. When are zeros significant to the right of a decimal (example: 2.00)?

Have 2 pairs share their answers with the class.

Note: If your classroom normally has graduated cylinders and objects available and your teacher has left them out with instructions, students may perform the actual displacement measurement activity in pairs. Otherwise, stick to the reading/discussion above.

Wrap-up / Exit Ticket (~10 min)

Have students answer the following on a half-sheet of paper to turn in:

1. In your own words, define accuracy and precision.
2. Explain the displacement method for measuring volume — what happens to the water level, and why does this help measure volume?
3. Is the zero in the number 1000 significant? Is the zero in 2.00 significant? Explain why, using the rule from the reading.

If Time Remains

Have students find a small object in the classroom (e.g., an eraser or a pen cap) and describe, in writing, how they would use the displacement method to measure its volume if they had a graduated cylinder and water — including what they would observe and record.