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HYPOTHESIS, THEORY, AND LAW SC.6.N.3.2How science really works

Objective: Students will be able to explain what a scientific law and theory are and give examples of each.

Essential Question: What are the differences between a scientific law and theory?

What is a scientific hypothesis?• A hypothesis is a possible answer to a scientific question.• A scientific hypothesis is not a guess!• Hypotheses are based on:

• Prior experience• Scientific background knowledge• Preliminary observations• Logic

In this class, we state hypotheses as “If, then, because” statements.

If the type of vehicle is changed, then a car will have a higher mpg rating than a truck, because lighter vehicles use less gas per mile than heavier vehicles.

Scientific HypothesisThe format of a good hypothesis:

If {tested/independent variable} is changed, then {prediction about outcome/dependent variable}, because {research that supports the prediction}.

The hypothesis should clearly state the predicted relationship between the tested/independent and outcome/dependent variables, and it must include the background knowledge you use to make that prediction.

Scientific Theory• Theories are not educated guesses either!

• Theories are explanations for how nature works.

• Theories explain a major phenomenon of nature.

• Phenomenon: any observable event

• Theories are well-supported with evidence, and are thought to be the best explanation of a phenomenon.

Examples of Theories• Theory of plate tectonics - is the theory that the outer rigid layer of the earth

(the lithosphere) is divided into a couple of dozen "plates" that move around across the earth's surface relative to each other, like slabs of ice on a lake.

Examples of Theories• Atomic theory - is the idea that matter is made up of little

units called atoms, or it can be defined as a theory of the structure of the atom

Examples of Theories• Cell theory– 1. All living things are made of cells. 2. Cells

are the basic units of structure and function in living things. 3. Living cells come only from other living cells

Examples of Theories• The scientific theory of evolution – A change in the genetic

composition of a population during succeeding generations, as a result of natural selection acting on the genetic variation among individuals, and resulting in the development of new species

Scientific Law• Scientific laws describe what nature does under certain

conditions.

• If those conditions are present, then the law can be used to make predictions about what will happen.

• Phenomenon A always happens when conditions 1 and 2 are met.

• Scientific laws are well-supported with evidence and have been tested repeatedly over time.

Relationship between theories and laws

• Theories DO NOT become laws with more evidence.

• Laws describe what happens and theories explain why it happens.

• Theories are used to explain why a law can be used to predict what will happen under certain conditions.

Examples of Laws• Law of universal gravitation~ states that the forces of

gravity acts between all objects in the universe

Examples of Laws• Law of superposition~ in undisturbed rock layers the

oldest layer will be at the bottom and the youngest layer at the top

Examples of Laws• Law of conservation of mass~ matter cannot be created

or destroyed, but it can change from one form to another

Examples of Laws• Law of conservation of energy~ energy cannot be created

or destroyed, but it can change from one form to another

DURABILITY OF SCIENCE SC.6.N.2.2How science really works

Objective: Students will be able to explain that scientific knowledge changes as new evidence is discovered or new interpretations are encountered.

Essential Question: Why does scientific knowledge change over time?

Scientific knowledge

0 Our knowledge of the natural world is always growing and changing.

0 Scientific knowledge is based on an ever-growing collection of facts about the natural world, but it changes with new evidence or new interpretations.

0Scientific knowledge changes when new evidence or new interpretations are encountered.

New evidence leads to change.

The shape of the Earth

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Aristotle (384–322 BC) stated his theory that the Earth was a sphere.

1.The gradual disappearance of ships over the horizon.2. The shadow of Earth on the Moon during a lunar eclipse is round.

His evidence:

Several years later

Geocentric Theory

Ancient Greece

Geocentric Model: Ptolemy (87-150 AD)

Supported by Ptolemy based on epicycles

Ptolemy’s system provided the model of our solar system for nearly

1500 years!! But… there was a problem…

1. This model does explain apparent motions of celestial (space) objects

2. Cannot explain Foucault’s Pendulum or the Coriolis Effect

Heliocentric Theory

Copernicus (1473-1543) 0Suggests a model that the Sun

was the center of the universe.0Argued that the motion of the

Sun & planets could be equally described by a Sun centered (heliocentric) system.

Tycho Brahe (1546-1601): the greatest of the pre-telescope observers in Europe.20+ years measuring the positions of the Sun, Moon and planets with great accuracy.

Johannes Kepler (1609)0 Johannes Kepler was an assistant to

Tycho Brahe. He used Brahe’s observations to study the orbit of Mars

0Discovered three laws of planetary motion: predict with accuracy the motions of the planets

0Galileo (1564-1642) first scientist to use a telescope to observe the sky. He observed the phases of Venus and the moons of Jupiter. Both observations supported the heliocentric model.