3. Outline
• The Scientific Method
• The Nature of Matter
• The Four Fundamental Forces
• The Elementary Particles
4. The Scientific Method
These steps make up a method which may be used to logically
solve problems in many other areas of life.
• Observation: a good scientist is observant and notices thing in
the world around him/herself. (S)he sees, hears, or in some other
way notices what’s going on in the world and becomes curious
about what’s happening.
• Question: the scientist then raises a question about what (s)he
sees going on. The question raised must have a “simple,” concrete
answer that can be obtained by performing an experiment.
• Hypothesis: this is a tentative answer to the question: a testable
explanation for what was observed. The scientist tries to explain
what caused what was observed.
• Prediction: Next, the experimenter uses deductive reasoning to test
the hypothesis.
• Testing: then, the scientist performs the experiment to see if the
predicted results are obtained. If the expected results are obtained,
that supports (but does not prove) the hypothesis.
5. An atom consists of a nucleus around which electrons orbit. The
nucleus is itself composed of particles called protons & neutrons.
A more modern view with the
A classical view of an atom.
electrons in “orbital clouds”.
6. Fundamental Forces
Associated Carrier Relative
Force Effect Range
Property Particle Strength
Infinite but
All masses attract
Gravitational Mass weakens with Graviton 10-36
each other
distance
Infinite but
Electric Opposites
Electromagnetic weakens with Photon 1
charge attract, likes repel
distance
Three colors ≈ 10-15 meters
Color combine to make (distance between
Strong Gluon 102
charge neutral protons in atomic
combinations nucleus)
Massive particles ≈ 10-18 meters
Weak
Weak decay to lower (1/1000th proton W&Z 10-7
charge
mass particles diameter)
7. Protons & neutrons are built of elementary
particles called quarks
ddu uud
u: up quark
d: down quark
9. Key Terms
• Atom: a submicroscopic particle consisting of a
nucleus & orbiting electrons. The smallest unit of a
chemical element.
• Electric charge: the electrical property of objects that
causes them to attract or repel one another. A charge
may be either positive or negative.
• Electromagnetic force: the force arising between
electrically charged particles, between charges &
magnetic fields, & between magnets. This force holds
electrons to the nuclei of atoms, makes moving charges
spiral around magnetic field lines, & deflects a
compass needle.
• Electron: a low-mass, negatively charged subatomic
particle. In an atom, electrons orbit the nucleus, but
may at times be torn free if ionized.
10. Key Terms
• Gluon: a particle that carries (or exerts) the strong force
between quarks.
• Gravitational force: force exerted on one body by
another due to the effect of gravity. The force is directly
proportional to the masses of both bodies involved & is
inversely proportional to the square of the distance
between them.
• Graviton: A theoretical particle having no mass and no
charge that mediates (carries) the gravitational force.
• Hypothesis: an explanation proposed to account for
some set of observations or facts.
• Law: in science, generally a theory that can be
expressed in a mathematical form.
11. Key Terms
• Model: a theoretical representation of some object or
system.
• Neutrino: tiny neutral particle with little or no mass &
immense penetrating power. These particles are
produced by stars when they fuse hydrogen into
helium.
• Neutron: a subatomic particle of nearly the same mass
as the proton but with no electric charge. Neutrons &
protons comprise the nucleus of the atom.
• Nucleus: the core of an atom around which its electrons
orbit. The nucleus has a positive electric charge &
comprises most of an atom’s mass.
• Photon: a particle of visible light or other
electromagnetic radiation.
12. Key Terms
• Proton: a positively charged subatomic particle. The
constituent of an atom’s nucleus that determines the
type of the atom.
• Quark: a fundamental particle of matter that interacts
via the strong force; basic constituent of protons &
neutrons.
• Scientific method: the process of observing phenomena,
proposing hypotheses to explain them, & testing the
hypotheses.
• Standard model: the current theoretical model that
describes the fundamental particles & forces in nature.
• Strong force (or nuclear force): the force that binds
quarks together & holds protons & neutrons in an
atomic nucleus.
13. Key Terms
• Theory: a hypothesis or set of hypotheses that have
become well-established through repeated & diverse
testing.
• Universality: the assumption that the physical laws
observed on Earth apply everywhere in the universe.
• Weak force: the force responsible for radioactive decay of
atoms.
