Lesson 13 of 15
The big picture
Show on a big screenA force is a push or a pull. A force changes how things move.
| Idea | Remember |
|---|---|
| A push or a pull | A force needs two objects. The unit is the newton |
| What a force does | It starts motion, changes speed, changes direction or reshapes |
| Touching, or not | Contact forces touch. Non-contact forces do not |
| Two at once | On one line: same way, add. Opposite ways, subtract |
| Balanced | The net force is zero. The motion stays the same |
| Unbalanced | The net force changes the motion |
| Friction | It acts against motion, or against the push to move. Rough means more |
| Friction both ways | Needed for grip. Reduced where it wastes effort |
| Weight and the spring balance | Weight is the pull of the Earth on an object. It is measured in newtons. For the smallest reading, divide a big gap by its equal spaces. |
| Mass stays, weight changes | Mass is the amount of matter. It is the same everywhere. Weight is the pull on an object. It changes from place to place. |
| The push a liquid gives | A liquid pushes up on an object. This push is upthrust. Weight bigger than upthrust: the object sinks. Both the same: it floats. |
Open Chapter 5, Exploring Forces, in your NCERT book. Read it with your teacher.