M ODELS

Q UESTION How do scientists explain how the world works, how it worked in the past, and how it will work in the future? What makes it hard to do this?

B LACK B OX Any system that cannot be observed and manipulated directly or understood completely. Some black boxes are incomprehensible because our sensory access to them is incomplete

E XAMPLE #1: D INOSAURS – EXISTED IN PAST

E XAMPLE #2: E ARTH ’ S C ORE – SEALED OFF FROM ACCESS

E XAMPLE #3: P LATE T ECTONICS

E XAMPLE #4: S OLAR S YSTEM

G EOCENTRIC V IEW OF S OLAR S YSTEM The idea that the sun is the center of the solar system was not discovered by renaissance astronomers, but rather hypostulated in 300 BC by Aristarchus of Samos. Aristarchus was a Greek astronomer who attempted to measure the relative distances and sizes of the earth, moon, and sun. Although his measurements were not very accurate he did propose that the sun was larger then the earth. This revelation made him consider that the sun was the center of the solar system (heliocentric). At the time the populous viewed the earth as center of the universe because why would the gods create the center of civilization on the earth, but not make it the center of the solar system.

B LACK B OX  M ODEL Gather a few facts about a black box, can develop a working idea about… what it looks like, how it works, what it is made of, etc. When we do the above, we are building a model

M ODEL Is a sufficiently accurate and complete representation or explanation of an object or process that is to some degree inaccessible. Communicates information about that object or process, and is often the basis for further inquiry and discourse Often develops in stages

E XAMPLE #W EATHER M ODEL

M ODEL S TAGES 1. Individual approaches an unknown (a black box), makes observations, and organizes those observations into a tentative model that explains the unknown 2. After collaboration and additional observation (testing)  model may be abandoned, revised, or confirmed 3. Eventually consensus evolves to explain the reality for everyone- until new information provides evidence for another revision of the model

D EFINITION OF M ODEL ( S ) Conceptual model – an idea that takes form of a description or explanation of an object, system, or action that is not completely understood

W HAT IS THE SMALLEST FORM OF MATTER ? eature=related

A RISTOTLE ~400 BCE 4 elements = air, earth, wind, fire (There are no such things as atoms) Each element had 2 qualities = dryness, coldness, hotness, wetness Atoms are continuously divisible (no smallest part of matter)

D EMOCRITUS ’ ‘A TOMOS ’ ~400 BCE ATOMOS = indivisible atom Void where there is space between atoms Solid hard balls, no internal structure, Unchangeable & homogeneous Atom is the smallest piece of matter

D ALTON 1808

A RISTOTLE V. D EMOCRITUS First real model that people believed. Prevailed over Democritus and idea of “atomos” for centuries

T HOMSON ’ S M ODEL : P LUM P UDDING M ODEL 1904 Plum pudding model - > positive background with negatively charged electrons Discovered sub-atomic particle called the electron. Negatively charged particle. Model is unstable

R UTHERFORD ’ S M ODEL : G OLD F OIL E XPERIMENT 1911 Discovered protons Discovered nucleus Helped to solve the mystery of the charge of the atom, but not the mass

B OHR M ODEL 1913 Specific orbits around nucleus Electrons travel in certain successively larger orbits Outer orbits hold more electrons Electrons can jump orbits and on way back down, emit light

C HADWICK M ODEL 1932 Discovered neutron

E LECTRON C LOUD M ODEL Model points 90% chance of finding an electron in the cloud How discovered? Used quantum physics to predict where electrons maybe Many different scientists, major contributor -> Schrödinger How different from previous model? Electrons travel in cloud vs. ‘rotaries’

P ICTURE OF AN A TOM

1948 Z ENITH C OLOR TV

R EAL W ORLD Scientists don’t have all the answers Apply the skills and procedures to discover things in the world that they can’t observe directly. Scientists have to rely on the best available model to explain how the world works, how it worked in the past, and how it will work in the future.

Y OUR CHALLENGE … What does the inside of your black box look like? Use all senses Build a conceptual model Collaborate Refine model, if necessary