--- title: "Newton's First & Second Laws" description: "State and apply Newton's First Law (an object stays at rest or constant velocity unless acted on by a resultant force) and Second Law (force = mass × acceleration), including the relationship between " canonical: https://lightmysky.com/learn/science/newtons-first-and-second-laws-mt_tXxxCFl32J source: https://lightmysky.com/learn/science/newtons-first-and-second-laws-mt_tXxxCFl32J.md retrieved: 2026-10-19 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Newton's First & Second Laws State and apply Newton's First Law (an object stays at rest or constant velocity unless acted on by a resultant force) and Second Law (force = mass × acceleration), including the relationship between mass, force, and acceleration Subject: Science · Area: Forces & Motion · Ages 12 to 13 Page: https://lightmysky.com/learn/science/newtons-first-and-second-laws-mt_tXxxCFl32J ## Ready when they can - States Newton's First Law and gives a real example (e.g. why a moving spacecraft doesn't need engines in space) - Uses F = ma to calculate force, mass, or acceleration given the other two quantities - Explains why a heavier object requires more force to achieve the same acceleration - Explains why seatbelts are needed in cars using Newton's First Law ## Lesson: Newton's First and Second Laws You already learned about resultant forces. Newton's First Law builds on that idea: an object at rest stays at rest, and a moving object keeps moving at the same speed and direction, unless a resultant force acts on it. **Example.** Once a spacecraft is moving through space, it can switch off its engines. There is hardly any air resistance or friction out there, so no resultant force acts on it. It keeps moving in a straight line at the same speed, sometimes for years, until something else pushes or pulls on it. **Tip.** In a moving car, your body travels at the same speed as the car. If the car stops suddenly, your body keeps moving forward, exactly as Newton's First Law predicts, until a force stops it. A seatbelt gives you that force safely. Newton's Second Law tells you how much force is needed to change motion. Force equals mass times acceleration, written as F = m × a. Pushing harder gives more acceleration. But a bigger mass needs more force to reach the same acceleration. *(drawing: With the same acceleration, the heavier trolley needs 20 N of force while the lighter bike only needs 10 N.)* One more word earns its place: acceleration. It means how quickly the speed changes, and it is measured in metres per second squared (m/s²). A cart that goes from standing still to 6 m/s in 3 seconds gains 2 m/s of speed every second, so its acceleration is 2 m/s². That is the a in F = m × a. **Recap.** An object keeps its motion unless a resultant force changes it, and F = m × a tells you exactly how much force that takes. ## Practice 32 questions on this page, each with its working shown. ## Needs first - [Resultant Forces](https://lightmysky.com/learn/science/resultant-forces-mt_AiWlJfvC3O) - [Speed & Distance-Time Graphs](https://lightmysky.com/learn/science/speed-and-distance-time-graphs-mt_q-1a86ydgU) - [Mass vs Weight](https://lightmysky.com/learn/science/mass-vs-weight-mt_sUVeVXzRuq) - [Air Resistance & Friction](https://lightmysky.com/learn/science/air-resistance-and-friction-mt_Y9k86G8BBT) ## Opens up - [Newton's Third Law](https://lightmysky.com/learn/science/newtons-third-law-mt_fbYbe3YSVj) - [Newton's Second Law with Numbers](https://lightmysky.com/learn/science/newtons-second-law-with-numbers-mt_Nn2MVJL7bO) - [Investigating Forces](https://lightmysky.com/learn/science/investigating-forces-mt_xkn2sf93WJ)