NCERT Solutions for Class 8th Science Chapter 5 .2 What Can a Force Do … · 5.3 Are Forces an Interaction Between Two or More Objects? — In-text Questions

The force applied on an object may

• make an object move from rest — a football lying still starts moving when it is kicked;
• change the speed of an object if it is moving — brakes slow a cycle down, pedalling speeds it up;
• change the direction of motion of an object — a bat turns a moving ball back;
• bring about a change in the shape of an object — a balloon flattens when pressed, dough spreads under a belan;
• cause some or all of these effects at once — a fielder's hands both slow a ball and turn it aside.

Yes — none of these take place without the action of a force.

So if you see a moving object speed up, slow down, stop, turn, or get squeezed or stretched, you can say with certainty that some force is acting on it, even if you cannot see what is applying it. The rolling ball that stops on its own is the standard example: something must be acting on it, and in the next section we find that it is friction.

At least two objects are involved in every single action, and yes — a force appears only when two objects interact.