In 1583 Galileo went to church one Sunday in the cathedral of his hometown of Pisa, Italy. During a boring service he noticed that the lamplighter had left one of the chandeliers swinging. He started timing the swings with his pulse and made an astounding discovery: as the swing decreased in amplitude, the time remained the same. He could scarcely wait to get back to his laboratory to make further tests with a pendulum. As a result of his experiments, he found that not only did amplitude of the swing have no effect on the time of the swing, but neither did the mass of the bob. Since gravity is the only force acting on the pendulum bob, he concluded that objects of different mass would fall at the same velocity. This was a revolutionary idea since everyone, including the contemporary scientists, knew for sure that a heavier object would fall faster; it was just common sense. But Galileo was convinced that he was right, so he proposed a demonstration; he would drop two balls, one wooden and one metallic, from the top of the Tower of Pisa to see whether the metal ball fell faster or not. It happened that the two balls hit the ground at the same time.
How could that be? Doesn't gravity pull harder on the heavier object? The answer is, yes it does, but it takes longer for the heavier object to get started. We call this "inertia," and it is defined as the tendency for a mass to remain at rest or remain in motion, and it varies directly as the mass. In other words, the greater the mass, the greater is the inertia. But we really don't know what causes this strange force that exactly counteracts gravity. Some believe it is an inherent property of matter; while others believe it is caused by the total outside gravitational force from the surrounding universe.
Another definition of inertia is a disinclination to move. This would be a good definition of some people; they are what you might call "slow starters," they have a lot of inertia. The Bible describes a few of these types. God had a tough time getting Jonah on his way to Ninevah; He told Abraham to move out and go to a far country; He told a reluctant Moses to go to Egypt and set His people free. There are also "fast starters," those who have less inertia, but faster is not always better. We think of Ahimaaz and Cushi, both fast runners. They both ran to give David news about the battle with Absalom; the faster Ahimaaz arrived first, but he had no message (2 Sam. 18:29), while Cushi arrived second with the news of Absalom's death (2 Sam. 18:32). Modern guided missiles have what is called an inertial guidance system composed of gyroscopes, accelerometers, and a computer to tell them where they are and where they are going. If we are to accomplish the gospel commission, we need to overcome our natural inertia, and we need the help of a divinely inspired "inertial guidance system."
