Which Cart Comparison Is Fair?

Use experimental descriptions to isolate force and mass variables.

Mr. S Teaches · Original starter mini-lesson · MS7-SCI-04

Learning objective

Choose a valid comparison and explain how force or mass relates to a change in motion.

Before you begin

Read a table and distinguish speed from a change in speed.

Gather your materials

Paper or notebook
Pencil and the passage, model directions or data printed in this lesson

Language to know

net force: The combined push or pull on an object, including direction.
mass: A measure of how much matter an object contains.
acceleration: A change in velocity over time.

Understand the concept

Fictional cart report: All carts start at rest on the same level track. Trial A: mass 1 kg, steady net force 2 N, speed after 2 s is 4 m/s. B: mass 1 kg, net force 4 N, speed after 2 s is 8 m/s. C: mass 2 kg, net force 2 N, speed after 2 s is 2 m/s. Timing and force measurements have uncertainty. Compare trials that change one factor; changing force and mass together makes the separate effects harder to infer.

Teach it step by step

Read the report and build a table with mass, net force and final speed as separate columns.
Compare A with B and identify the single changed factor.
Compare A with C and identify the single changed factor in that pair.
Plan repeat trials and specify what would be measured consistently before making a causal claim.

Make the thinking visible

Worked example or model response

A and B have the same mass and timing; doubling the net force is associated with twice the final speed from rest in these idealized results. A and C keep force constant; doubling mass produces a smaller speed change. B and C alter both mass and force and are not the cleanest comparison.

Guided practice

Together explain why “B is fastest because it has the greatest mass” is contradicted by the report. Cite the relevant masses.

Independent practice

Plan a fourth trial that tests mass while holding net force at 4 N. Predict its final speed for a 2 kg cart under this ideal model and name two controls.

Quick assessment

If two forces on a cart are equal and opposite, does that necessarily mean the cart is motionless?

Answer key & assessment criteria

Answers and teaching guidance

Guided: B has mass 1 kg, whereas slower C has mass 2 kg; the claim misreads the mass column.
Independent: Use 2 kg and 4 N on the same level track for 2 s from rest. The ideal prediction is 4 m/s; controls include start condition, track and time.
Quick check: No. Zero net force means no change in velocity in the ideal model; a moving cart could keep moving steadily.

Look for: Look for a claim that answers this lesson’s question, accurate use of the supplied evidence and an explanation of a limit or alternative. Ask the learner to point to the detail supporting each inference.

Make it work for your learner

More support

Draw force arrows and physically pair table rows before calculating or predicting.

Extension challenge

Critique how unmeasured friction would affect a report that lists applied force instead of net force.

Selected contributions · Official sources

Standards connections

Selected NGSS band contribution; not complete performance expectation coverage.

Contributes to NGSS performance expectation

MS-PS2-2

NGSS · Grades 6–8 band

Investigate how force and mass affect changing motion.

Read the official performance expectation ↗

Learners plan comparisons and interpret idealized data. They do not conduct the investigation, and a full performance would require measurements, evidence quality checks and repeated trials.

Source and mapping checked 2026-11-04. This mini-lesson contributes selected skills; it does not claim full attainment.

Supporting Common Core literacy connection

RST.6-8.1

Common Core · Grades 6–8

Support scientific-text analysis with specific evidence.

Read the official standard ↗

The provided scientific passage/model is explicitly analyzed in the activity. This selected literacy practice does not establish subject-content alignment or complete coverage of the standard.

Source and mapping checked 2026-11-04. This mini-lesson contributes selected skills; it does not claim full attainment.

A curriculum map. A place to start.

These 96 original mini-lessons sample selected skills across grades 6–8. This is a starter curriculum map and lesson collection, not a complete year of daily instruction, every standard, or an accredited course.

Contributes to Common Core standard identifies a selected math or English skill. Grade-specific codes retain their actual grade. Science and social studies use a Supporting Common Core literacy connection only for the reading or writing activity described; this does not establish subject-content alignment.

Contributes to NGSS performance expectation describes a partial science connection to a grades 6–8 band expectation. A paper model or short data task does not fulfill the entire performance expectation. Each mapping explains its limits. Science and social studies grade placements are suggested; course sequences vary.

Visual arts, music and computing may be electives or rotations. Course availability and health/PE requirements vary. Where no verified subject-content mapping is recorded, the lesson states Subject-content alignment not yet verified. Any supporting Common Core activity is identified separately.

Use North Carolina’s Standard Course of Study ↗ for local planning. No NC alignment is claimed without a verified crosswalk. Standards are briefly paraphrased here; use each official source for its full wording.