The 42nd Period | STEM Education Hub

Distance and displacement sound like they should mean the same thing — until you actually walk them out. Today you and a partner will mark a number line on the floor, walk two different paths along it, and measure both quantities for real. Bring your numbers, not your assumptions.

🎯 Goals

Measure distance and displacement for the same walked path using real tools.
Build a physical, felt sense of why displacement can be smaller than distance — or zero.
Practice computing average speed from a measured distance and a timed interval.
Produce a data table you can defend: numbers you measured, not numbers you assumed.

🧰 Materials

📏Meter stick or tape measure

🧻Masking tape or floor chalk (for marking the number line)

⏱️Stopwatch (a phone works)

📓Physics notebook or the printed data sheet

Section 1 of 4

Set Up the Number Line

Choose a straight, open stretch of floor.

A hallway, the classroom perimeter, or an outdoor sidewalk all work. You need at least 12 meters of straight-line space.

Mark it off in 1-meter (or 2-meter) increments with tape or chalk.

Label the starting end “0 m” and number each mark going outward. This is your x-axis for the day — every position you record is a distance along this line from the 0 m mark.

⚠️ Keep the line straight. A curved or bent line will throw off your distance measurements.

Assign roles.

One partner walks, one partner times with the stopwatch and calls out the walker's position at the turnaround and stopping points. Switch roles between Walk 1 and Walk 2 so both partners get to walk and time.

Section 2 of 4

Walk 1 — One-Way Trip

Pick a starting mark and an ending mark.

Record x_i (start) and x_f (end) on your data sheet before you walk.

Time the walk from start to finish.

The timer starts the stopwatch the instant the walker steps off, and stops it the instant the walker reaches the ending mark.

Calculate.

Find distance (the length of ground actually covered), displacement (Δx = x_f − x_i), and average speed(distance ÷ time). For a one-way trip in a straight line, two of these numbers should match — figure out which two, and why.

📓 Physics Notebook

For Walk 1, is distance equal to the size of the displacement? Why does that make sense for a trip that never changes direction?

Section 3 of 4

Walk 2 — Out and Back

Pick a starting mark, a turnaround mark farther down the line, and a final mark.

Your final mark should be somewhere other than exactly back at the start — for example, start at 0 m, walk out to 8 m, then walk back to 3 m.

Time the entire trip, start to finish — including the turnaround.

Don't stop the stopwatch at the turnaround point. You're timing the whole two-leg trip as one continuous motion.

Calculate distance, displacement, and average speed for the whole trip.

Add up both legs for distance. Use only the start and final position for displacement — the turnaround point does not appear anywhere in the displacement calculation.

⚠️ This is the step where most groups make an error. If your distance and displacement come out equal for Walk 2, check your work — a trip with a turnaround should not give you the same number for both.

Trial	x_i (m)	x_f (m)	distance (m)	displacement (m)	time (s)	avg speed (m/s)
Walk 1 — One-way
Walk 2 — Out & back

This table is for in-class use. Copy your final values onto your printed data sheet or notebook to turn in — this page does not save your entries.

📓 Physics Notebook

For Walk 2, distance and displacement came out different (or, if you walked all the way back to your exact starting mark, displacement came out as zero). Explain in your own words why the turnaround point matters for distance but disappears completely from the displacement calculation.

Section 4 of 4

Conclusion

Question 1

Describe a real trip you take often (walking to class, driving somewhere) where your distance traveled is much larger than your displacement. What makes the two so different in that case?

Question 2

Could an object have a large displacement but a small (or zero) distance traveled? Explain why or why not.

Question 3

Two walkers cover the same distance in the same time on Walk 2, but one ends up with a bigger displacement than the other. What would have to be different about how they walked?

📤 Turn In

Completed data table for both walks (x_i, x_f, distance, displacement, time, average speed)
Written answers to the three Conclusion questions
One sentence, in your own words, defining distance and displacement so that the difference is unmistakable

← Back to Activity 1-1-1 Overview Review the Deep Dive →Keep your data sheet — you'll want this same intuition for Project 1-1-4.