--- title: "Force & Motion Vocabulary" description: "Use balanced forces, unbalanced forces, resultant force, acceleration, deceleration, speed, moment, lever, fulcrum and mechanical advantage to explain and predict how forces affect an object's movemen" canonical: https://lightmysky.com/learn/science/force-and-motion-vocabulary-mt_F3ATPTCYm6 source: https://lightmysky.com/learn/science/force-and-motion-vocabulary-mt_F3ATPTCYm6.md retrieved: 2026-11-12 --- > **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`. # Force & Motion Vocabulary Use balanced forces, unbalanced forces, resultant force, acceleration, deceleration, speed, moment, lever, fulcrum and mechanical advantage to explain and predict how forces affect an object's movement and turning. Subject: Science · Area: Forces & Motion · Ages 9 to 11 Page: https://lightmysky.com/learn/science/force-and-motion-vocabulary-mt_F3ATPTCYm6 ## Ready when they can - Distinguish between balanced and unbalanced forces and describe the effect of each on an object's motion - Use 'resultant force' correctly when describing the net effect of two or more forces acting on an object - Apply 'moment', 'lever', and 'fulcrum' correctly when describing how simple machines work ## Lesson: Force & Motion Vocabulary A force is a push or pull with a size and a direction. Forces on one object are balanced when their resultant is zero. For straight-line movement, balanced forces keep motion unchanged: a resting object stays at rest, and a moving object keeps the same speed and direction. Forces can still be acting. *(drawing: These bars compare force sizes. The two pulls act in opposite directions on one object and cancel. Their resultant is zero.)* The resultant force combines all forces on one object, including their directions. It can be zero. A nonzero resultant means unbalanced forces. Force is measured in newtons (N). On one line, forces pointing the same way add: 6 N right + 2 N right = 8 N right. Opposite forces subtract: 6 N right and 2 N left leave 4 N right. *(drawing: The line tracks a force total, not the object's position. The opposite forces leave a resultant of 4 N right.)* Speed tells how fast an object moves. A speed of 2 metres per second (2 m/s) means 2 metres each second. An object accelerates when its speed or direction changes. Slowing down is also acceleration, often called deceleration. A resultant along its movement speeds it up. One against its movement slows it while it keeps moving that way. A sideways resultant can change its direction. *(drawing: The cart keeps moving in the same direction. Its speed increases, so it accelerates.)* A lever is a stiff bar turning around a pivot called the fulcrum. A moment, or torque, is a force's turning effect. A downward push on a level lever gives a larger moment with more force or more distance from the fulcrum. **Example.** A resting, level seesaw balances when opposite moments are equal. A heavier friend can balance a lighter friend by sitting closer to the fulcrum. Ignore the bar's weight and pivot friction here. Effort is your applied force; output force is the lever's force on the load. Mechanical advantage compares these force sizes. Keep the load and fulcrum fixed on a level lever: pushing downward farther out needs less effort. Not every lever increases force. **Recap.** Balanced forces have a zero resultant. Unbalanced forces change movement. A lever turns around its fulcrum. A moment is a force's turning effect. *This lesson, its questions and its flashcards were written for this learning dataset.* ## Practice 12 questions on this page, each with its working shown. ## Needs first - [Forces Vocabulary](https://lightmysky.com/learn/science/forces-vocabulary-mt_GBY8enpzO0) ## Opens up - [Resultant Forces](https://lightmysky.com/learn/science/resultant-forces-mt_AiWlJfvC3O) - [Levers, Pulleys & Gears](https://lightmysky.com/learn/science/levers-pulleys-and-gears-mt_Q2k3fSwyzQ)