Big Idea 3: The Role of Theories, Laws, Hypotheses, and Models Description   The terms that describe examples of scientific knowledge, (e.g. "theory," "law," "hypothesis," and "model“) have very specific meanings and functions within science.

Benchmark Number & Descriptor SC.7.N.3.1 Recognize and explain the difference between theories and laws, and give several examples of scientific theories and the evidence that supports them. SC.7.N.3.2 Identify the benefits and limitations of the use of scientific models.

SCIENTIFIC THEORY A scientific explanation to a pattern in the natural world Many observations and much evidence is needed in order to create a valid theory. Scientific investigation is a key part when creating theories. Theories may be supported by scientific evidence at the time but may be incorrect. Evidence may change with time; better technology Example: Geocentric (earth in middle of solar system) to Heliocentric model (sun in middle of solar system)

EXAMPLES of SCIENTIFIC THEORIES Big Bang Theory The universe has expanded from hot, dense, gaseous conditions. Tectonic Plate Theory The surface of the earth is composed of tectonic plates, which move slowly. Atomic Theory All matter is made up of atoms. Theory of Matter and Energy Matter and Energy are always conserved. Cell Theory Cells form the foundation, the basic unit of all living organisms. Theory of Evolution All life on earth evolved from simple forms.

SCIENTIFIC LAW This is a statement of fact meant to describe, in concise terms, an action or set of actions. It is generally accepted to be true and universal, and can sometimes be expressed in terms of a single mathematical equation. Scientific laws are similar to mathematical postulates. They don’t really need any complex external proofs; they are accepted at face value based upon the fact that they have always been observed to be true. Specifically, scientific laws must be simple, true, universal, and absolute. They represent the cornerstone of scientific discovery, because if a law ever did not apply, then all science based upon that law would collapse. Some scientific laws, or laws of nature, include the law of gravity, Newton's laws of motion, the laws of thermodynamics, Boyle's law of gases, the law of conservation of mass and energy, and Hook’s law of elasticity. http://wilstar.net/theories.htm

EXAMPLES of SCIENTIFIC LAWS Ohm’s Law I = V/R Relationship between current, voltage, and resistance Named after Georg Ohm Newton’s Law s Objects at rest/motion stay at rest/motion until a force acts on it. Objects will accelerate in the direction of the force (F = M*A). Action-Reaction forces (equal and opposite) Law of Segregation For any pair of characteristics there is only one gene in a gamete even though there are two genes in ordinary cells. Founder – Gregor Mendel Ideal Gas Law Combination of Charles's and Boyle’s gas laws. Formula: pV = nRT Relates pressure, temperature, and volume of gasses For additional laws see this website: http://en.wikipedia.org/wiki/List_of_scientific_laws_named_after_people

KNOWLEDGE CHECK What is the difference between a scientific theory and a scientific law? Can a scientific theory change over time? Why? List 2 examples of scientific theory and scientific law.

KNOWLEDGE CHECK What is the difference between a scientific theory and a scientific law? Laws are generalizations about what has happened; Theories are explanations of observations (or of laws). Can a scientific theory change over time? Why? Yes, as technology progresses, new evidence can be discovered helping to justify or falsify a theory. List 2 examples of scientific theory and scientific law. Theory: Atomic theory, Big Bang theory; Law: Newton’s Laws, Law of Segregation

WHAT’S IN A MODEL?

MODELS Models are a visual representation that help scientists study something in more depth. There are 2 general types of models: Physical Models that you can touch Representation of an item they want to study Mathematical Made up of math equations and data They allow you to calculate things.

MODELS BENEFITS LIMITATIONS Models can be used for the following: Study objects that are too small to see Study objects that are too large to see Help explain the past and the present Help predict the future Scientists must realize the limitations of models, especially when reading the information obtained by them. Because we may not see an actual picture, models are thoughts and ideas from our heads. Some calculations are very complex, and computers are needed to find the answer.

KNOWLEDGE CHECK Why do scientists use models? Describe the two main types of scientific models. List 2 benefits of using models. List 2 limitations when using models.

KNOWLEDGE CHECK Why do scientists use models? To help create a visual representation when studying something in more depth. Describe the two main types of scientific models. Physical – Hands on model; Mathematical – equation providing data List 2 benefits of using models. To help explain the past and the present, study objects that are too small/large to see List 2 limitations when using models. Some physical models are subjective since they are based on theories/observations; since some theories need computers to solve them, scientists must be able to read and interpret the data.