Fundamentals of physics Mechanics UNIT 5 5.0 Aristotelian vs. Galilean Motion...

Fundamentals of physics - Mechanics Background - Aristotle’s Ideas on Motion ---------------------------------------------------------------------------------------- Aristotle thought that natural motion proceeds from the "nature" of an object which depended on the combination of four elements – earth, water, air, and fire. Ancient Greek scientists were familiar with some of the ideas in physics that we study today more than 2000 years ago. Aristotle was considered the most outstanding philosopher-scientist of his time in ancient Greece.

Fundamentals of physics - Mechanics Background - Aristotle’s Ideas on Motion ---------------------------------------------------------------------------------------- Aristotle divided motion into two main classes: natural motion and violent motion Aristotle thought that natural motion proceeds from the "nature" of an object which depended on the combination of four elements – earth, water, air, and fire.

Fundamentals of physics - Mechanics Background - Aristotle’s Ideas on Motion ---------------------------------------------------------------------------------------- Aristotle divided motion into two main classes: natural motion and violent motion Aristotle thought that natural motion proceeds from the "nature" of an object which depended on the combination of four elements – earth, water, air, and fire.

Fundamentals of physics - Mechanics Background - Aristotle’s Ideas on Motion ---------------------------------------------------------------------------------------- Aristotle divided motion into two main classes: natural motion and violent motion… In natural motion objects were returning to their proper place in the universe… Violent motion were caused by pushes and pulls on objects... In his view, every object in the universe has a proper place, determined by this "nature“. Any object not in its proper place will "strive" to get there. An unsupported lump of clay, being of earth, properly falls to the ground while being of the air, an unimpeded puff of smoke properly rises.

Fundamentals of physics - Mechanics Background - Aristotle’s Ideas on Motion ---------------------------------------------------------------------------------------- Aristotle divided motion into two main classes: natural motion and violent motion… In natural motion objects were returning to their proper place in the universe… Violent motion were caused by pushes and pulls on objects... A feather being a mixture of earth and air but predominantly earth, properly falls to the ground, but not as rapidly as a lump of clay. He postulated that heavier objects would strive harder. Thus objects should fall at speeds proportional to their weights: the heavier the object, the faster it should fall.

Fundamentals of physics - Mechanics Background - Aristotle’s Ideas on Motion ---------------------------------------------------------------------------------------- Aristotle divided motion into two main classes: natural motion and violent motion… In natural motion objects were returning to their proper place in the universe… Violent motion were caused by pushes and pulls on objects... Things on Earth showed natural motion which was either straight up or straight down while celestial objects had circular motion. Unlike up-and-down motion, circular motion has no beginning or end, repeating itself without deviation. He asserted that celestial bodies are perfect spheres made of a perfect and unchanging substance.

Fundamentals of physics - Mechanics Background - Aristotle’s Ideas on Motion ---------------------------------------------------------------------------------------- The movement of the water (in all cases) is natural but the debris is violent motion in that it is externally caused and imparted to objects... They moved not by their "nature," but because of pushes or pulls... Pushing or pulling forces produced Violent motion and so was imposed motion. Pushing a cart or lifting a heavy weight imposed motion, as the wind imposed motion on ships and floodwaters imposed it on boulders and debris.

Fundamentals of physics - Mechanics Background - Aristotle’s Ideas on Motion ---------------------------------------------------------------------------------------- Aristotle’s ideas of motion became so much a part of traditional knowledge that hundreds of years after Newton and Galileo we still intuitively use them... There were difficulties with the concept of violent motion e.g. a bowstring moved an arrow until the arrow left the bow. Thereafter the arrow's motion seemed to require some other pushing agent. Aristotle's statements about motion were a beginning in scientific thought, and, although we don’t agree with him now, for nearly 2000 years his views were beyond question....

Fundamentals of physics - Mechanics Background - Aristotle’s Ideas on Motion ---------------------------------------------------------------------------------------- Aristotle’s ideas of motion became so much a part of traditional knowledge that hundreds of years after Newton and Galileo we still intuitively use them... This lead to the thinking that since the force required to move the earth is inconceivable then it must be the centre of the universe... The thinking was so entrenched that it was heresy to think otherwise...

Fundamentals of physics - Mechanics This new idea was to overturn the conception of the cosmos... Nicolaus Copernicus ---------------------------------------------------------------------------------------- Nicolaus Copernicus (1474-1543) formulated a theory of the moving Earth. Copernicus reasoned that the simplest way to account for the observed motions of the Sun, Moon, and planets through the sky was to assume that Earth (and other planets) circle around the Sun. He feared persecution so he kept his hypothesis secret.

Fundamentals of physics - Mechanics This new idea was to overturn the conception of the cosmos... Nicolaus Copernicus ---------------------------------------------------------------------------------------- Also he could not explain what made the Earth move. Aristotle's views had become so entrenched in Church doctrine that to contradict them was to question the Church itself. Many Church leaders considered the idea of a moving Earth as a threat, not only their authority, but the very foundations of faith and civilization as well.

Fundamentals of physics - Mechanics Galileo and the Leaning Tower ---------------------------------------------------------------------------------------- Galileo discredited the Aristotelian ideas about motion, through observation and experiment Galileo was not the first to point out difficulties in Aristotle's views, but he was the first to provide conclusive evidence by dropping objects of various weights from the top of the Leaning Tower of Pisa and comparing their falls

Fundamentals of physics - Mechanics Galileo and the Leaning Tower ---------------------------------------------------------------------------------------- Contrary to Aristotle's assertion, many observers witnessed the dropping of two objects of different weight from the top of the tower hitting the ground together. While Aristotle's views appear logical and consistent with everyday observations and do seem to make common sense, unless you purge it from your concept of motion, you will experience difficulty understanding the physics of motion... It is understandable that many scoffed at the young Galileo and continued to hold fast to their Aristotelian teachings despite the evidence.

Fundamentals of physics - Mechanics Galileo's Inclined Planes ---------------------------------------------------------------------------------------- Galileo showed that physics should be investigated by experiment rather than logic… In this way he can be considered the father of modern investigative methods used in the way we study modern science... On Earth motion always involved a resistive medium such as air or water. Aristotle did not consider motion in the absence of an interacting medium. Aristotelian motion required that an object requires a push or pull to keep it moving.

Fundamentals of physics - Mechanics Galileo's Inclined Planes ---------------------------------------------------------------------------------------- Galileo showed that physics should be investigated by experiment rather than logic… In this way he can be considered the father of modern investigative methods used in the way we study modern science... Galileo disagreed with this principle and he postulated that if there is no interference with a moving object, it will keep moving in a straight line forever; no push, pull, or force of any kind is necessary. Galileo tested this hypothesis by experimenting with the motion of various objects on plane surfaces tilted at various angles.

Fundamentals of physics - Mechanics Galileo's Inclined Planes ---------------------------------------------------------------------------------------- Balls rolling on downward sloping planes speed up ... Balls rolling on upward sloping planes slow down... Prediction: balls rolling along a horizontal plane would neither speed up nor slow down Galileo tested his hypothesis by experimenting with the motion of various objects on plane surfaces tilted at various angles. Balls rolling on downward sloping planes picked up speed Balls rolling on upward sloping planes lost speed.

Fundamentals of physics - Mechanics Galileo's Inclined Planes ---------------------------------------------------------------------------------------- Balls rolling on downward sloping planes speed up ... Balls rolling on upward sloping planes slow down... Prediction: balls rolling along a horizontal plane would neither speed up nor slow down From this he predicted that balls rolling along a horizontal plane would neither speed up nor slow down. The ball would finally come to rest not because of its "nature" but because of friction.

Fundamentals of physics - Mechanics Galileo's Inclined Planes ---------------------------------------------------------------------------------------- Balls rolling on downward sloping planes speed up ... Balls rolling on upward sloping planes slow down... Prediction: balls rolling along a horizontal plane would neither speed up nor slow down This idea was supported by observation of motion along smoother surfaces. The motion of objects persisted for a longer time when there was less friction. Lessening the friction caused the motion afforded a greater to approached constant speed

Fundamentals of physics - Mechanics Galileo's Inclined Planes ---------------------------------------------------------------------------------------- Balls rolling on downward sloping planes speed up ... Balls rolling on upward sloping planes slow down... Prediction: balls rolling along a horizontal plane would neither speed up nor slow down Lessening the friction caused the motion afforded a greater to approached constant speed He predicted that, in the absence of friction or other opposing forces, a horizontally moving object would continue moving indefinitely.

Fundamentals of physics - Mechanics Galileo's Inclined Planes ---------------------------------------------------------------------------------------- Galileo placed two of his inclined planes facing each other. A ball released from a position of rest at the top of a downward sloping plane rolled down and then up the slope of the upward sloping plane until it almost reached its initial height.

Fundamentals of physics - Mechanics Galileo's Inclined Planes ---------------------------------------------------------------------------------------- He inferred that only friction prevented it from rising to exactly the same height, for the smoother the planes, the more nearly the ball rose to the same height. Reducing the angle of the upward sloping plane causes the ball to rise to the same height as before, but will never reach its initial height.

Fundamentals of physics - Mechanics Galileo's Inclined Planes ---------------------------------------------------------------------------------------- Balls rolling on upward sloping planes lost speed. Balls rolling on downward sloping planes picked up speed He hypothesized that balls rolling along a horizontal plane should neither speed up nor slow down. The ball would finally come to rest not because of its "nature" but because of friction

Fundamentals of physics - Mechanics Galileo's Inclined Planes ---------------------------------------------------------------------------------------- The motion of objects persisted for a longer time when there was less friction; reducing the friction makes the motion approached constant speed. He predicted that, in the absence of friction or other opposing forces, a horizontally moving object would continue moving indefinitely.

Fundamentals of physics - Mechanics Galileo's Inclined Planes ---------------------------------------------------------------------------------------- The property of an object to resist changes in motion is called inertia... Aristotle did not imagine motion without friction so physics got stuck for 2000 years... Galileo realized that friction was a force like any other push or pull and so developed the idea of inertia... Thus Newton presents a completely new concept of the Universe... Newton's laws are really a restatement of the concept of inertia as proposed earlier by Galileo. The tendency of the ball is to move forever without slowing down in the absence of retarding forces. The property of an object to resist changes in motion is called inertia. In the absence of retarding forces, the tendency of the ball is to move forever without slowing down.

Fundamentals of physics - Mechanics Galileo's Inclined Planes ---------------------------------------------------------------------------------------- Aristotle did not imagine motion without friction so physics got stuck for 2000 years. Galileo realized that friction was a force like any other push or pull and so developed the idea of inertia… The property of an object to resist changes in motion is called inertia... Aristotle did not imagine motion without friction so physics got stuck for 2000 years... Galileo realized that friction was a force like any other push or pull and so developed the idea of inertia... Thus Newton presents a completely new concept of the Universe... Newton's laws are really a restatement of the concept of inertia as proposed earlier by Galileo.

Fundamentals of physics - Mechanics Galileo's Inclined Planes ---------------------------------------------------------------------------------------- Thus the Earth of any other celestial body did not need to be constantly pushed for them to show movement... So now onto Newton's Laws of Motion… The property of an object to resist changes in motion is called inertia... Aristotle did not imagine motion without friction so physics got stuck for 2000 years... Galileo realized that friction was a force like any other push or pull and so developed the idea of inertia... Thus Newton presents a completely new concept of the Universe... Newton's laws are really a restatement of the concept of inertia as proposed earlier by Galileo.

End of UNIT 5 5.0 Aristotelian vs. Galilean Motion ...