The 42nd Period | STEM Education Hub

You already know how to read a graph. Today you find out how much of that skill transfers when the vertical axis changes — and where your instincts from Lesson 1-1-2 will actively work against you if you're not paying attention.

🎯 Goals

Read velocity from the height of a v-t graph, not its slope.
Find acceleration from a v-t graph's slope and directly from an a-t graph's height.
Determine speeding up vs. slowing down by comparing the signs of velocity and acceleration.
Calculate displacement over an interval using the area under a v-t graph.
Feel the height-not-slope distinction by walking a target v-t graph with the motion detector's velocity readout.

🧰 Materials

📄Graph station handouts (v-t and a-t graphs, Day 1)

📡Motion detector set to velocity-mode display (Day 2)

📐Grid paper or graph handout

📓Physics notebook

DAY 1

Graph Stations

Section 1 of 4

Warm-Up — Read the Line, Differently

Look at the sample v-t graph without reading ahead.

Answer out loud with your partner: at each segment, is the object moving in the positive direction, the negative direction, or standing still? Read this straight from the height, not the slope.

Sample graph — your station handouts have several like this, plus matching a-t graphs.

Now identify which segments show acceleration and which show none.

A segment with a flat top or bottom has zero acceleration, no matter how far above or below zero it sits.

Section 2 of 4

Station Rotation — v-t and a-t Graphs

Rotate through the station handouts with your partner.

Each station has a different v-t or a-t graph. Break each one into segments where the slope (or height, for a-t graphs) changes.

For each segment, record velocity (or acceleration), acceleration (if it's a v-t graph), and whether the object is speeding up or slowing down.

Speeding up requires velocity and acceleration to share a sign. Slowing down requires them to have opposite signs. A segment with zero acceleration is neither — it's cruising.

⚠️ Don't assume 'positive acceleration' automatically means speeding up. Check the sign of velocity in that same segment before you decide.

Segment	Velocity (height)	Acceleration (slope)	Speeding up / slowing down?
Segment A (0–4 s)
Segment B (4–7 s)
Segment C (7–14 s)

In-class scratch space only — copy your final answers onto your station handout to turn in.

📓 Physics Notebook

Find one segment across all your stations where the object was slowing down. What were the signs of velocity and acceleration in that segment, and how did you use those two signs — not just one of them — to reach your answer?

DAY 2

Walk a Target Velocity-Time Graph

Section 3 of 4

Set Up and Predict

Set the motion detector's display to velocity mode instead of position mode.

Confirm with your teacher that you're seeing a v-t graph, not the x-t graph from Project 1-1-4.

Before walking, predict what a 'flat' section of your target graph will feel like to walk.

In Project 1-1-4, a flat section meant standing still. Today, a flat section on your target means walking at a steady, unchanging pace — write down your prediction for how that will feel different.

Section 4 of 4

Walk It, Compare, Reflect

Walk your target velocity-time graph in front of the sensor.

Try to match each segment's height (speed and direction) and each transition's slope (how quickly you speed up, slow down, or hold steady).

Print or save your resulting graph and compare it to the target.

Identify at least one segment where your walk matched well and one where it didn't, and name what went wrong using height/slope/area vocabulary.

📓 Physics Notebook

Compare walking a flat section today to standing still for Project 1-1-4. Which one was physically easier to hold steady, and why do you think that is?

Question 1

Explain, using both an x-t graph and a v-t graph, why 'the line is flat' means something different depending on which graph you're looking at.

Question 2

An object has positive velocity and negative acceleration. Is it speeding up or slowing down? What if both velocity and acceleration were negative instead? Explain both using the sign rule from today.

Question 3

Sketch (describe in words) a v-t graph whose area above the time axis exactly cancels its area below the axis over some interval. What does that tell you about the object's net displacement over that interval — and does it mean the object didn't move at all?

📤 Turn In

Completed Day 1 station handouts — velocity, acceleration, and speeding-up/slowing-down for each segment
Your Day 2 walked graph printout, alongside the original target graph
Written answers to the three Conclusion questions

← Back to Activity 1-2-1 Overview Review the Deep Dive →Next up: Lesson 1-2-2, The Kinematic Equations.