Patterns of Motion and Equilibrium Lecture 1 1.Aristotle in Motion 2.Galileo’s Concept of Inertia 3.Mass- a Measure of Inertia

1.1 Aristotle in Motion ( 2000 years ago) Objects are some combination of four elements: earth, water, air and fire Natural motion proceeds form the nature of the objects. Every object in the universe has a proper place determined by his nature and if not in its proper place it will strive to get there. Examples: a lump of clay, being of earth falls to ground, a puff of smoke, being of air, rises, a feather falls slowly to he ground because it is a mixture of air and earth Heavier objects would fall faster than lighter ones.

1.1 Aristotle in Motion Types of motion 1.Natural motion: either straight up or straight down. Different rules apply in the heavens (celestial objects) 2.Violent motion: push or pull (wind on ships, water on tree trunks). Motion here is externally caused not by the nature of the objects, but because of impressed force. Problem:

1.2 Galileo’s Concept of Inertia Except for the effect of air friction, objects of different weights fell to the ground in the same amount of time Force is needed to start an object moving but no force is needed to keep it moving. When friction is absent, a moving object needs No force to keep it moving. It will remain in motion by itself. (inertia)

1.2 Galileo’s Concept of Inertia Effect of gravity and friction Moving objects tend to remain moving without the need of an imposed force. Objects at rest tend to remain at rest. This property of objects to maintain their state of motion is called inertia.

1.3 Mass- a measure of inertia The amount of inertia an object has depends on the amount of matter in the object: mass Mass: the quantity of matter in an object (kilogram) Weight: the force upon an object due to gravity (Newton)