NCERT Solutions for Class 8th Science Chapter 5 Exploring Forces
Updated on 2026-09-19
About this chapter
A force is a push or a pull on an object that comes out of the object's interaction with another object . At least two objects must interact for a force to come into play. The SI unit of force is the newton , symbol N . A force can make a resting object move, change the speed of a moving object, change its direction of motion , change its shape , or produce several of these effects together. None of these changes happens without a force. Contact forces act only when the surfaces touch — muscular force and the force of friction . Friction arises from the irregularities of the two surfaces locking into each other, always acts opposite to the motion (or attempted motion), and is greater on rough surfaces. Non-contact forces act across a gap — magnetic force , electrostatic force and gravitati
- Chapter opener
- .1 What Is a Force?
- .3 Are Forces an Interaction Between Two or More Objects?
- .4.1 Contact forces
- .4.2 Non-contact forces
- .5 Weight and Its Measurement (Fig. 5.12)
- .5 Weight and Its Measurement
- .5 Weight and Its Measurement · Table 5.2 (Fig. 5.14)
- .6 Floating and Sinking
- .6 Floating and Sinking (Fig. 5.15)
Quick revision
| Term | What it means | Where it comes in the chapter | Example from the book |
|---|---|---|---|
| Force | A push or a pull on an object, resulting from its interaction with another object | Sections 5.1 and 5.3, pages 63–65 | Pushing, pulling or lifting a cardboard box (Activity 5.1, Fig. 5.1) |
| Newton (N) | The SI unit of force, and therefore also of weight | Section 5.3, page 65 | The spring balance of Fig. 5.13 reads up to 10 N |
| Contact force | A force that acts only when the two objects are physically in contact | Section 5.4.1, page 66 | Muscular force and the force of friction |
| Muscular force | The force produced when muscles contract and elongate | Section 5.4.1, page 66 | Bullocks pulling a cart; heart muscle circulating blood |
| Friction | The force that comes into play when an object moves or tries to move over another surface; always opposite to that motion | Section 5.4.1, pages 67–68 | A pushed lunch box slides some distance and stops (Activity 5.3) |
| Non-contact force | A force whose effect is felt even when the objects are not in contact | Section 5.4.2, page 69 | Magnetic, electrostatic and gravitational force |
| Magnetic force | The force a magnet exerts on another magnet or on a magnetic material | Section 5.4.2, page 69 | A ring magnet floating above another with like poles facing (Activity 5.5) |
| Electrostatic force | The force a charged body exerts on another charged or uncharged body | Section 5.4.2, pages 70–71 | A rubbed plastic scale picking up small pieces of paper (Activity 5.6) |
| Gravitational force (gravity) | The force with which the Earth attracts objects towards itself; it is always attractive | Section 5.4.2, page 72 | Every object thrown up comes back to the ground (Activity 5.8, Fig. 5.10) |
| Weight | The gravitational force with which the Earth pulls an object; measured in newton | Section 5.5, pages 72–75 | A 1 kg object weighs 10 N on the Earth but only 1.6 N on the Moon |
| Mass | The amount of matter in an object; measured in g or kg and the same at every place | Section 5.5, page 75 | The same object is 1 kg on the Earth, the Moon, Mars, Venus and Jupiter |
| Upthrust / buoyant force | The upward force a liquid applies on an object placed in it | Section 5.6, page 76 | A closed empty bottle pushed into water bounces back up (Activity 5.13) |
Exercises
- Chapter opener — Probe and ponder Page 62
- .1 What Is a Force? — Activity 5.1: Let us explore Page 635
- .2 What Can a Force Do to the Objects on Which It Is Applied? · Table 5.1 — Activity 5.2: Let us analyse Page 645
- .2 What Can a Force Do … · 5.3 Are Forces an Interaction Between Two or More Objects? — In-text Questions Page 655
- .3 Are Forces an Interaction Between Two or More Objects? — A step further Page 655
- .4 What Are the Different Types of Forces? · 5.4.1 Contact forces — A step further Page 665
- .4.1 Contact forces — In-text Questions Page 675
- .4.1 Contact forces — Activity 5.3: Let us investigate Page 675
- .4.1 Contact forces — Activity 5.4: Let us explore Page 685
- .4.1 Contact forces — In-text Questions Page 685
- .4.1 Contact forces — A step further Page 685
- .4.2 Non-contact forces — In-text Questions Page 695
- .4.2 Non-contact forces — Activity 5.5: Let us test Page 695
- .4.2 Non-contact forces — Activity 5.6: Let us experiment Page 705
- .4.2 Non-contact forces — Activity 5.7: Let us experiment Page 705
- .4.2 Non-contact forces — In-text Questions Page 715
- .4.2 Non-contact forces — Activity 5.8: Let us observe Page 715
- .4.2 Non-contact forces — In-text Questions Page 725
- .5 Weight and Its Measurement (Fig. 5.12) — Activity 5.9: Let us explore Page 735
- .5 Weight and Its Measurement — Activity 5.10: Let us observe Page 735
- .5 Weight and Its Measurement — Activity 5.11: Let us calculate Page 745
- .5 Weight and Its Measurement · Table 5.2 (Fig. 5.14) — Activity 5.12: Let us measure Page 745
- .5 Weight and Its Measurement — In-text Questions Page 755
- .6 Floating and Sinking — In-text Questions Page 765
- .6 Floating and Sinking (Fig. 5.15) — Activity 5.13: Let us investigate Page 765
- Chapter-end exercise, Questions 1–10 — Keep the curiosity alive Page 77
- Interdisciplinary projects — Discover, design, and debate Page 79