I do my understand why Newton's first law states that when resultant force is zero, an object moves at constant velocity. Shouldn't the object not move since it's resultant force is zero?
Answers (1)
Newton first assumed that a body, which is in born moving. In that case if we donot apply any net force then the body will never stop. Gallileo did an experiment. He took a plane slope connected with a plane floor. Then he took a ball and left it on the top of the slope. He found the ball rolling down from the slope and also found the ball moving on floor with a constant speed. As the floor was plane, it was friction less and so there was no force to retard the motion of the ball and that is why Gallileo found the ball moving at constant speed on the floor. Seeing this experiment Newton concluded his 1st law of motion.