Craig C. Freudenrich
Scientists in the Renaissance era challenged many physical concepts that had been touted by ancient Greek and Roman philosophers. The concept of force and motion, a major area of physics, provides an excellent example. More specifically, let's look at what happens when an archer shoots an arrow.
The Greek philosopher Aristotle proposed that objects move because a force pushes on them constantly. An archer exerts a force on the arrow by pulling back and releasing the bowstring. Once the arrow leaves the bow, some other external force must push the arrow through the air.
In the 16th century, an Italian scientist named Galileo challenged Aristotle's idea. Galileo realized that the force of friction between materials opposes motion. That would mean that moving objects only need external forces to keep them moving when friction is present. Galileo conducted experiments with balls rolling on inclined planes and horizontal surfaces (rolling balls have minimal friction). Here are some of Galileo's findings:
- Balls rolling downhill speed up because gravity pulls on them (in the direction of motion).
- Balls rolling up an inclined plane slow down because gravity pulls against them (opposite the direction of motion).
- Balls rolling on a level surface -- in the absence of friction -- roll at a constant speed (gravity is neither pushing nor pulling on them).
Galileo did a second series of experiments with two inclined planes. A ball rolling down an inclined plane and then up a second plane set at the same angle will roll to the same height that it started from. When Galileo reduced the angle of the second plane, the ball still traveled to the same initial height, even though the distance was longer. When Galileo reduced the angle of the second plane further, he always found the same result. He realized that if the second inclined plane was a horizontal surface, the ball would keep rolling forever so long as there was no friction.
Galileo concluded that objects resisted changes in their motion. This resistance was a property that he called inertia. He rejected the notion that an object in motion needs an external force to remain in motion (Aristotle's idea). Instead, he said, a moving object would stay in motion in a straight line at a constant speed, unless an external force (e.g., friction) acted on it. Sir Isaac Newton later formulated Galileo's idea into Newton's first law of motion or the law of inertia. Renaissance scientists helped advance physics by challenging old ideas.(Gregor Schuster/Getty Images)
One of the most significant ways Renaissance thinkers pushed our physics knowledge forward was to take the Earth out of the center of the universe. In the 16th century, Nicolaus Copernicus's observations and measurements led him to state that the sun, not the Earth, is at the center of the universe. Galileo Galilei pushed Copernicus's point with further proofs, angering religious leaders and getting tried for heresy.
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