PHYS 141 Chapter Notes - Chapter 2: Geocentric Model, Heliocentrism, Time Point
21 Sep 2018
School
Department
Course
Professor
Chapter 2: Motion in 1 Dimension
Intro
• Dynamics: the study of motion and physical concepts
• Kinematics: the branch of dynamics that describes motion without considering the
forces that cause the motion
• Geocentric model: the ancient idea that the Earth was the center of the universe
o Promoted by Aristotle
o Was prevailing model until seventeenth century
• Heliocentric model: the idea that the Earth and other planets orbit the Sun
o Credited to Copernicus
o Replaced geocentric model
2.1 Displacement
• Frame of reference: coordinate system that defines starting point for measurement
• Displacement x of an object is its change in position
o x= xf-xi
▪ Where xf is coordinate of final position and xi is coordinate of initial
position
o SI unit is the meter
• , or “delta,” signifies change in physical quantity
• A positive x means a displacement in the positive x-direction, where a negative x
means a displacement in the negative x-direction
• Example of a position-vs-time graph
• Displacement is a vector quantity
o Vector quantities have both magnitude and direction
▪ Often indicated by boldface type with an arrow over the letter
Document Summary
2. 1 displacement: frame of reference: coordinate system that defines starting point for measurement, displacement x of an object is its change in position. Instantaneous velocity v is the limit of the average velocity as t approaches zero: v=lim t 0 x t. V t=v v t t: si unit: m/s2, a=lim t 0 v t, can be determined for a given time on a position vs. time graph by the slope of the line tangent to the curve. Instantaneous speed of an object is a scalar quantity and is equal to magnitude of the instantaneous velocity. Whe(cid:374) the(cid:455) a(cid:396)e i(cid:374) opposite di(cid:396)e(cid:272)tio(cid:374)s, the o(cid:271)je(cid:272)t"s speed de(cid:272)(cid:396)eases (cid:449)ith ti(cid:373)e (cid:894)(cid:862) lo(cid:449)i(cid:374)g do(cid:449)(cid:374)(cid:863)(cid:895). Instantaneous acceleration instantaneous acceleration, a, is the limit of the average acceleration as t approaches zero. If you were to convert it into a velocity versus time graph, the velocity would increase or decreases at a constant rate (a).
