Brief history of the knowledge of motion
Copernicus (1473 - 1543) - Published theory of moving earth in his De Revoltionibus in 1543.
Galileo Galilei (1564 - 1642) - first to provide alternate description of motion which discredited Aristotle's ideas. Galileo had experimental evidence to support his theories. He used rolling objects on inclined planes to observe the nature of motion. He acknowledged the existence of friction and identified the concept of inertia as a result. Galileo's theory was that if there is no interference with a moving object it will keep moving in a straight line forever, no sustained push or pull required.
FRAME OF REFERENCE
The object or background used to determine motion and its direction. The frame of reference is assumed/defined to be at rest. Everything around us has motion ( you, the wall, the air,...). There is no matter that we know of that does not have some type of motion associated with it.
Has to start in one position and have at least one change in that position during a period of time. The study of motion requires three basic measurements:
DIRECTION ( ) - How the position changes relative to the starting point: north, south, east, west; positive and negative; up, down, left, right; etc.
TIME (t) - Duration of an event from start to finish. Time as we define it appears to be irreversible and is commonly measured in seconds (s), minutes (min), hours (hr), etc.
VELOCITY ( v ) - The speed and direction of the motion. Velocity involves a change in position known as displacement ( Dx ). D stands for ‘change in’ or ‘final - initial’ and x represents position. For an object to have a velocity the initial and final positions must be different. Velocity is calculated by dividing the displacement by the time interval - v = Dx/Dt Instantaneous velocity is measured at a specific point (instant). Average speed is the total displacement divided the total time of the event.
FREEFALL - this is a special case that occurs with objects falling near the surface of the earth. In order to simplify the study of accelerated motion we will often ignore any outside effects, such as friction. When an object falls here on earth there is friction between it and the air which changes as the object accelerates. This variable acceleration is more difficult to deal with mathematically and conceptually and will be reserved for the next unit conceptually. We can, however, closely approximate the “constant” acceleration of an object near the earth’s surface if we neglect the air friction. Although this sounds ridiculous, many common objects falling a short distance experience such small amounts of air friction it has little effect on the objects’ motion. For example, a golf ball, tennis ball, and a bowling ball will all fall at the same rate (~9.8 m/s2)from a height of one to two meters. Again, the idea is to start off simple, then add in the complicating issue of friction next unit.