Newton’s First Law

Overview

In this lesson (6 of 15) in Exploring Systems in Motion, students develop an explanation of Newton’s First Law by observing what happens when forces are unbalanced or balanced. They complete short investigations and use evidence to connect the law to real-life situations.

Learning intentions

• Students will be able to explain Newton’s First Law using the idea of net force and inertia.
• Students will observe and describe motion in demonstrations involving balanced and unbalanced forces.
• Students will connect Newton’s First Law to safe, real-world examples (seat belts, friction, sports, vehicle stopping).
• Students will communicate their understanding using scientific vocabulary and evidence from observations.

Success criteria

• I can state Newton’s First Law and describe what it means for objects with zero net force.
• I can predict how an object’s motion changes (or doesn’t change) based on balanced/unbalanced forces.
• I can use observations from the demonstrations to support my explanation.
• I can describe inertia as an object’s tendency to resist changes in motion.

Curriculum links

• Forces and motion: explain how forces affect changes in motion and relate net force to motion.
• Scientific investigation and communication: gather observations, identify patterns, and communicate conclusions using evidence.
• Skills: use science vocabulary accurately and support claims with data/observations.
• Inquiry and reasoning: predict outcomes, analyze results, and revise explanations.

Lesson structure (45 minutes)

1. 0–5 min — Hook: “Why does it keep going?” Show a quick scenario (e.g., a cart rolling after a push). Ask: “What would happen if the push stopped?” Students turn-and-talk to share ideas about what keeps motion going.

2. 5–10 min — Mini-lesson: Newton’s First Law Use a simple statement: an object continues in its state of motion unless acted on by a net external force. Explain inertia as resistance to change, and clarify that “no change” means constant velocity, not necessarily “not moving.” Keep language concrete and connect to classroom experiences (books on a desk, sliding friction).

3. 10–20 min — Demo A: Balanced forces Demonstrate with a low-friction setup or friction-controlled surface (teacher push with minimal net force). Students observe whether the cart keeps moving at the same speed/direction. They record observations in a short table: initial state, what changes, evidence.

4. 20–30 min — Demo B: Unbalanced forces Demonstrate an opposite condition (e.g., adding a surface with more friction or attaching a mass/force). Students predict before the demo, then observe changes in speed and/or direction. They record evidence and answer a prompt: “What is the net effect of the forces?”

5. 30–38 min — Guided application: Real-world connection In pairs, students choose one scenario: seat belt/airbag, stopping distance, pushing a shopping cart, sports follow-through, or roller coasters near the crest. They answer:

• What helps keep motion the same (balanced/near-zero net force)?
• What causes motion to change (unbalanced net force)? Provide a sentence frame for support: “According to Newton’s First Law, ___ will continue to ___ unless ___.”

6. 38–45 min — Exit ticket: Claim + evidence Students complete a short response:

• Define Newton’s First Law in their own words.
• Use one piece of evidence from the demos to explain why the motion changed (or didn’t).

Resources

• Carts (or toy cars), track/strip, masking tape markers for positions
• Low-friction surface option (smooth track) and higher-friction option (felt/rug strip)
• Assistive materials: ramps, small weights (as allowed), spring scale or simple force aids for teacher use
• Student recording sheet with two columns: Balanced vs Unbalanced observations
• Scenario cards for the real-world application
• Exit ticket slips or digital form (no internet required)

Assessment

• Formative: teacher circulates during demos to check predictions and observation notes.
• Formative: guided application responses are reviewed for correct use of “net force,” “balanced/unbalanced,” and inertia.
• Summative (small): exit ticket checks accurate explanation and evidence-based reasoning.

Differentiation

• ESL support: provide sentence frames and a word bank (force, net force, balanced, unbalanced, inertia, constant velocity, change in speed/direction). Allow drawing/diagrams as part of responses.
• Reading/processing support: present key steps orally and visually; keep prompts short; model one example together before independent work.
• SEN support: offer reduced writing options (e.g., 2–3 sentence response + labeled diagram). Provide a checklist for exit ticket components.
• Extension: ask students to add an “if…then” prediction using a new condition (e.g., double the push, add more friction) and justify using net force and inertia.