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Laws of Motion

Observing the motion of objects on inclined surfaces, Galileo deduced that objects move with a constant speed when no force acts on them.



He observed that when a marble rolls down on an ideal, frictionless plane, inclined at both sides, its velocity increases as it falls under the unbalanced force of gravity. As it rolls up opposite the inclined plane, its velocity decreases. Galileo argued that the marble would try to achieve the same height from which it was released. If the angle of inclination of the slope on the right-hand side was reduced gradually, the marble, in striving to reach the same height, would travel a greater distance to reach the same height. So, if the right side inclined plane was made horizontal, the marble would continue to travel forever in order to reach the same height it was released from. The unbalanced forces on the marble are now zero, which means an external unbalanced force is required to change the motion of the marble but no net force is required to help the marble continue its uniform motion. Practically it is not possible to achieve zero unbalanced force because of friction, acting opposite to the direction of motion. So the marble stops after travelling some distance.

In this chapter we’ll study the relationship between force and the state of motion of a body.This relationship is given by the three laws of motion called Newton’s Laws of Motion. Newton studied Galileo’s ideas on force and motion and presented the three laws which govern the motion of objects.


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