One Monday, when Martin came back from school on the bus, he noticed something that he had never paid attention to before.
— How was your day, son? — Asked his mother. P>
— Okay, but there's something I don't understand. Today he was on the bus almost asleep in a seat, and he suddenly stopped. From the impulse I almost ended up sitting on the ground! — exclaimed the boy.
His mother looked at him worried.
— Are you okay? Have you hurt yourself?
— I'm fine, but the people who were standing ended up all pressed against the driver — said Martín.
— And what is your question? — Asked his mother. P>
— I can't find why that happened.
— That's because of the law of inertia! — Martin's mother said.
— The law of inertia? he asked.
— To change the speed of an object, you need to apply a force to it. An object that is at rest or still is going to stay that way unless we apply a force to it. On the other hand, if it is moving, it will continue moving unless we apply another force to it — his mother explained. P>
— But I was still, why did I move forward? Martin asked confused.
— But you weren't resting — she said.
— Yes, I told you I was almost asleep — repeated Martín.
— It could be, but you were inside a bus that was moving. The force that made you stop was the same force that made you move.
— And what happens if there is an object in motion and there is no force to stop it? Martin asked.
— Then it will continue at a constant speed.