Start a ball rolling down a bowling alley and you’ll find that it moves slightly slower with time. Does this violate Newton’s law of inertia? Defend your answer.
ANSWER: First of all, Newton’s law of inertia states that: Until an external force acts on the system, the motion of the system will be unaffected. Which means the object in rest will be at rest and the object in motion will continue it’s motion with same speed and same direction until an external force acts on it. But, for the case given in the question, after rolling the ball, the speed of the ball decreases slightly with time. But there was a condition in Newton’s law of inertia, which is, until an external force acts. As we can easily verify that, there is friction between the surface of the bowling alley and the surface of the ball. As there is a frictional force, so the velocity has to be decreased. Because frictional force acts in the opposite direction of motion. CONCLUSION: The decrease in speed does not violate Newton’s 1st law of inertia and it is consistent with the law. There is a force and the speed gets decreased.