C a Let Us Study In the previous lesson, you have learned Newton's laws of motion which provided the framework for the understanding of how forces and motion are related. Recall that motion is the change in position relative to a frame of reference. Before Isaac Newton came up with his laws of motion, a lot of great thinkers have already laid the foundation for the study of force and motion. One of them was the Greek philosopher Aristotle. In his great text Biggie-a, Aristotle explained that objects have a natural place which they seek. For instance, objects made of wood, rock, and metal tend to seek out the Earth as that is their natural place to be. This is natural motion. But when a stone is lifted or thrown, it goes against its natural motion and so he called it violent motion. Violent motion just means an external force is applied to move objects. Consider a ball rolling across the ground. It eventually comes to rest. Aristotle would have said that since we are no longer rolling the ball, we are no longer exerting a violent action on it. Thus, its natural place is to come to rest. This however was proven to r- \"mm:- 2 be not true. Objects in motion come to rest due to friction. In the absence of friction, objects in motion remain in motion this is what inertia is all about. What is Inertia? Inertia is the tendency of an object to resist changes in its state of motion. Inertia is dependent on mass which means that the greater mass an object has, the greater its inertia will be. Inertia is not a force. Galileo and His Concept of Inertia Galileo Galilei was an Italian scientist who rst explained the concept of inertia. He did not believe Aristotle's idea that the ball came to rest because it desired to be in its natural state. He wanted to challenge and disprove that or'lodox belief. He showed that experiment rather than logic is the best test of knowledge. He wanted to test his hypothesis on motion. What will happen to the speed and direction of a moving object if there is no interference along its way? Will it eventually stop, or will it continually move forever? Let us nd out how Galileo asserted that force is not necessary to sustain horizontal motion. Galileo tested his theory in an experiment using two inclined planes. When the ball was rolled from one inclined plane to the next, it almost reached the height from which it was released as shown in Figure 1 below. If the steepness of the second inclined plane is decreased, the ball would still reach the same height from the point it was released [Figure 2}. Finally, he then ......_..-....:I '1... n......_.:l .'_..1.*_...:I ._'I.._.. .._.:I ..-..4...1....:l 4.1... 1....11 ....'I'I...:l .1....... \"Tim"... I\" O