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Scientific Theories
Scientific Laws
Atomic Theory- developed by John Dalton in the mid
18th century, the theory explains that all matter is
composed of elements made from indestructible
particles called atoms. It allowed Dalton and his
contemporaries to explain a number of chemistry
puzzles they were trying to solve, especially laws like
Lavoisier’s conservation of matter and the laws of
definite proportions and multiple proportions.
Newton’s Laws of Motion- three laws proposed by
Isaac Newton in the mid 17th century that describe the
relationship between forces and motion. They helped
scientists make sense of forces and motion, and created
a break from the Aristotelian views still held at that
time.
1st law: Law of Inertia
2nd law: F=ma
3rd law: Law of reciprocal forces
Kinetic Molecular Theory- developed in the mid 18th
century by James Clerk, the theory explains that gases
- consists of tiny particles
- in constant motion
- colliding elastically
- the velocity of which is in direct proportion to the
temperature.
It replaced Newton’s idea that gas pressure was created
by repulsion between the particles of gas.
Law of Conservation of Matter.- first clearly stated by
18th century chemist Antoine Lavoisier, this law
describes that in a closed system, matter is not created or
destroyed.
Mass of reactants = Mass of products
Germ Theory- developed by Louis Pasteur in 1861,
the theory explains that contagious diseases are caused
by invisible microorganisms. It helped replace the ideas
at that time that disease was caused by bad smells or
simply bad luck. Understanding the germ theory lead to
breakthroughs in preventing and treating disease.
The Ideal Gas Law- four simple gas laws developed
over two centuries, including Boyle’s Law and
Charles’s Law, can be combined to describe the
behavior of an ideal gas with the equation PV=nRT.
Boyle’s: pV=k
Charles’s: (V/T)=k
Gay-Lussac’s: (P/T)=k
Avogadro’s: (V/n)=constant
Theory of Natural Selection- described by Charles
Darwin in the mid 19th century, this theory explains
that competition for limited resources results in
differential reproductive success. Only organisms welladapted to their environment survive and pass on
hereditable traits. It explains the diversity of life on
earth, the fossil record, as well as why we currently
have antibiotic resistance.
Mendel’s Laws: developed by Gregor Mendel in the
mid 19th century.
Law of Independent Assortment: traits are passed on to
offspring independent of each other;
Law of Segregation: offspring receive one factor for a
trait from the mother and one from the father.
Theory of Plate Tectonics- this theory explains that
the earth’s crust is divided into plates that move. It
explains why we have tropical fossils in the Antarctic,
as well as why earthquakes and volcanoes occur in
certain zones.
Ohm’s Law: published in 1826 by Georg Ohm, this law
describes the relationship between electrical voltage,
current and resistance.
V=iR
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