--- title: "Resultant Forces" description: "Describe forces as vector quantities with both magnitude and direction, distinguish between balanced forces (zero resultant, no change in motion) and unbalanced forces (non-zero resultant, causes acce" canonical: https://lightmysky.com/learn/science/resultant-forces-mt_AiWlJfvC3O source: https://lightmysky.com/learn/science/resultant-forces-mt_AiWlJfvC3O.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`. # Resultant Forces Describe forces as vector quantities with both magnitude and direction, distinguish between balanced forces (zero resultant, no change in motion) and unbalanced forces (non-zero resultant, causes acceleration or deceleration) Subject: Science · Area: Forces & Motion · Ages 11 to 12 Page: https://lightmysky.com/learn/science/resultant-forces-mt_AiWlJfvC3O ## Ready when they can - Explains what a vector quantity is and why force is a vector - Calculates the resultant force when two forces act in the same or opposite directions on an object - Explains what happens to an object's motion when forces are balanced vs unbalanced - Draws free body diagrams showing all forces on a stationary object (e.g. a book on a table) ## Lesson: Finding the Resultant Force A force isn't just how hard you push or pull. It also has a direction. Anything with both a size and a direction is called a vector quantity. Force is a vector, so a 5 newton push to the right is not the same as a 5 newton push to the left, even though the size is equal. **Example.** Dog A pulls a sled forward with 40 newtons. Dog B pulls the same sled, same direction, with 30 newtons. Because both forces point the same way, you add them: 40 N + 30 N = 70 N forward. That total is called the resultant force. *(drawing: Both teams pull with 30 N, but in opposite directions. The pulls cancel out, so the resultant force is 0 N and the rope stays still.)* **Tip.** To find a resultant force: if the two forces point the same way, add them. If they point opposite ways, subtract the smaller from the larger. The resultant points in the direction of the bigger force. **Example.** A book sits still on a table. Gravity pulls it down. The table pushes back up with a normal force of equal size. These two forces are balanced, so the resultant force is 0 N and the book doesn't move. If you then push the book sideways harder than friction can hold it, the forces become unbalanced and the book accelerates. With three or more forces, add the ones pointing the same way first, then subtract the rest. You can also work backwards from the resultant. If an object stays still, the resultant is 0 N, so the forces must balance: a 16 N pull to the left needs a 16 N pull to the right to cancel it. If the resultant is not zero, the object accelerates the way the resultant points: 44 N to the right against 27 N to the left leaves 44 N - 27 N = 17 N to the right, so the object moves right. **Recap.** Same-direction forces add together; opposite-direction forces subtract. A zero resultant means balanced forces and no change in motion; a non-zero resultant means unbalanced forces and acceleration. ## Practice 28 questions on this page, each with its working shown. ## Needs first - [Pushes & Pulls](https://lightmysky.com/learn/science/pushes-and-pulls-mt_B3W5EfimJw) - [Force & Motion Vocabulary](https://lightmysky.com/learn/science/force-and-motion-vocabulary-mt_F3ATPTCYm6) - [Drawing Force Diagrams](https://lightmysky.com/learn/science/drawing-force-diagrams-mt_k7GOtslF-x) - [Contact & Non-Contact Forces](https://lightmysky.com/learn/science/contact-and-non-contact-forces-mt_lcf8lx-LkZ) ## Opens up - [Vectors, Scalars and Free-Body Diagrams](https://lightmysky.com/learn/science/vectors-scalars-and-free-body-diagrams-mt_erzORFj2-1) - [Deformation & Fluid Pressure](https://lightmysky.com/learn/science/deformation-and-fluid-pressure-mt_fkwcCB5px7) - [Efficiency, Sankey diagrams, and work done](https://lightmysky.com/learn/science/efficiency-sankey-diagrams-and-work-done-mt_JyfLtl_nhw) - [Newton's First & Second Laws](https://lightmysky.com/learn/science/newtons-first-and-second-laws-mt_tXxxCFl32J) - [Moments, Pressure & Hooke's Law](https://lightmysky.com/learn/science/moments-pressure-and-hookes-law-mt_vuNjYx3qOy)