Objects that are lighter or less streamlined take a longer time to reach the bottom. With this technique, he established the following facts:Īll heavy, streamlined objects (for example a steel rod dropped point-down) reach the bottom of the tank in about the same amount of time, only slightly longer than the time they would take to fall the same distance in air. First, he experimented with objects falling in water, which probed the same issues but made the motion slow enough that he could take time measurements with a primitive pendulum clock. Anyone can speculate, but Galileo went beyond speculation and came up with two clever experiments to probe the issue. Why is it that some objects, like the coin and the shoe, have similar motion, but others, like a feather or a bit of paper, are different? Galileo speculated that in addition to the force that always pulls objects down, there was an upward force exerted by the air. This contradicted Aristotle's long-accepted idea that heavier objects fell faster. Galileo was the one who changed the course of history because he was able to assemble the observations into a coherent pattern, and also because he carried out systematic quantitative (numerical) measurements rather than just describing things qualitatively.įigure a: Galileo dropped a cannonball and a musketball simultaneously from a tower, and observed that they hit the ground at nearly the same time. It is inconceivable that Galileo was the first person to observe a discrepancy with Aristotle's predictions. Aristotle's observations had been incomplete, his interpretation a vast oversimplification. Galileo, who had a flair for the theatrical, did the experiment by dropping a bullet and a heavy cannonball from a tall tower. It looks like they hit the ground at exactly the same moment. Now repeat the experiment, but make it into a race between the coin and your shoe. Europeans believed him for two thousand years. That's why Aristotle wrote that heavy objects fell more rapidly. The paper takes much longer to hit the ground. Stand up now and simultaneously drop a coin and a bit of paper side by side. But there is something impressively consistent, universal, and inexorable about the way things fall. If one stretch of a river flows more rapidly than another, it may be only because the channel is narrower there, which is just an accident of the local geography.

A walking person who speeds up is making a conscious choice. Other examples seem less likely to have deep significance. The early pioneers of physics had a correct intuition that the way things drop was a message directly from Nature herself about how the universe worked. The motion of falling objects is the simplest and most common example of motion with changing velocity. To understand the concept and properties of acceleration.

Freefall position and velocity graphs