--- title: Pushes, pulls, friction and wheels — a lesson of Mova's school · trees and pragmatics description: «Pushes, pulls, friction and wheels», a lesson of the world course of Mova's primary school, sentence by sentence with dependency trees and pragmatics. It begins: When two forces on an object are equal and opposite, they are balanced, and the object does not change its movement. --- [Mova](https://md.mova.elamur.ai/free/en/) · [this page in HTML](https://mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/) [home](https://md.mova.elamur.ai/free/en/) / [corpora](https://md.mova.elamur.ai/free/en/corpora/) / [school](https://md.mova.elamur.ai/free/en/corpora/school/) / [World](https://md.mova.elamur.ai/free/en/corpora/school/world/) / Pushes, pulls, friction and wheels # Pushes, pulls, friction and wheels Lesson 85 of the world course of Mova's primary school: 22 sentences, each with its syntax tree and pragmatics. The lessons are written for Mova, and their agreed trees are part of Mova corpus 0.4 (CC BY-SA 4.0). How Mova does on its tests: [the lesson at school](https://md.mova.elamur.ai/free/en/school-run/world/85-pushes-pulls-friction-wheels/). - [0](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/0/) — When two forces on an object are equal and opposite, they are balanced, and the object does not change its movement. - [1](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/1/) — In a tug of war with two equally strong teams, the rope stays still. - [2](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/2/) — When one force is bigger, the forces are unbalanced and the object speeds up, slows down or changes direction. - [3](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/3/) — A moving object keeps moving until a force stops it. - [4](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/4/) — A puck slides a long way on ice because there is little friction to slow it. - [6](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/6/) — Friction can be a helper or a nuisance. - [7](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/7/) — It lets tyres grip the road, shoes grip the floor and brakes stop a bike. - [8](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/8/) — But it also wears things out and turns movement into wasted heat, so we use oil and grease to make parts slide smoothly. - [9](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/9/) — A wheel makes moving heavy things much easier, because rolling makes far less friction than sliding. - [10](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/10/) — Dragging a heavy box across a floor is hard, but the same box on a trolley rolls easily. - [11](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/11/) — Ball bearings, tiny steel balls inside a wheel's hub, let the wheel turn on its axle with very little friction. - [13](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/13/) — Balanced forces are equal and opposite, so they do not change an object's movement. - [15](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/15/) — A moving object keeps moving until a force such as friction stops it. - [16](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/16/) — Seat belts hold you when a car stops suddenly and your body keeps moving forwards. - [17](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/17/) — Heavier objects need a bigger force to start them moving or to stop them. - [18](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/18/) — Friction helps tyres, shoes and brakes to grip. - [19](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/19/) — Friction wears surfaces away and turns movement into heat. - [20](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/20/) — Oil and grease reduce friction between moving parts. - [21](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/21/) — Rolling makes much less friction than sliding, which is why wheels help. - [22](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/22/) — Ball bearings help a wheel turn smoothly on its axle. - [23](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/23/) — The grooves in tyres push water away so the tyres can grip a wet road. - [24](https://md.mova.elamur.ai/free/en/corpora/school/world/85-pushes-pulls-friction-wheels/24/) — Forces are measured in newtons with a forcemeter. - ← previous: [Mirrors, shadows and colours](https://md.mova.elamur.ai/free/en/corpora/school/world/84-mirrors-shadows-colours/) - next →: [Building strong things: bridges, towers and shapes](https://md.mova.elamur.ai/free/en/corpora/school/world/86-building-strong-things/) - ↑ back to [World](https://md.mova.elamur.ai/free/en/corpora/school/world/)