NCERT Solutions Curiosity Chapter 5 .4.1 Contact forces — Activity 5.3: Let us investigate
Book page 675 Updated on2026-09-05
Q1.
Gently push it and observe (Fig. 5.5). Does it stop after travelling some distance? Is there a force acting on it which brings it to rest?
Answer
Yes on both counts. The lunch box slides a certain distance and comes to rest, and yes, a force brings it to rest — the force of friction between the base of the box and the table.
Your hand pushed the box only at the start; after that nothing is touching it except the table. Yet its speed keeps falling. Since speed cannot change without a force, a force must be acting, and it must act opposite to the direction in which the box is sliding — a backward force is the only kind that can reduce speed.
Friction acts along the surfaces in contact, in the direction opposite to the motion, and brings the box to rest.
Why it happens: even a table top that feels smooth carries a large number of minute irregularities, and so does the base of the box (Fig. 5.6). Pressed together, these irregularities lock into each other and oppose any effort to move one surface over the other.
Q2.
Now repeat by pushing the object in the opposite direction. Does it stop again after travelling some distance?
Answer
Yes, it stops again — and after roughly the same distance, because it is sliding on the same pair of surfaces.
This is the useful half of the activity. Friction did not act towards a fixed side of the room; when you reversed the motion, friction reversed too. This tells us that friction has no direction of its own — it always acts opposite to the direction in which the object is moving or trying to move.
Check it yourself: now push the box very gently, so gently that it does not move at all. Friction is still acting — this time opposing your attempt to move it. That is why the definition says moves or tries to move.