1. Our Universe and the Forces
that Hold it Together

2. A few key concepts you need
to know first!

3. Only a theory?

4. Some basic definitions
• Fact: an observation that has been
repeatedly confirmed (If you drop a
pencil on Earth, it falls)
• Law: a descriptive generalization
about how the physical world
behaves (Laws of Motion)
• Hypothesis: a testable statement
that can be used to make
explanations

5. Some basic definitions
• Theory: a well-substantiated
and accepted explanation
that incorporates facts, laws,
and tested hypotheses.
In science, you don’t get
any better than a theory.

6. 2. Elements-substances that consist of just
one type of atom; they cannot be broken
down to other substances
1. Atom-the basic unit of all matter; the
smallest unit of matter that retains the
properties of an element

7. Is brass an element?
What about:
Oxygen O2
Water H20
Helium He

8. The structure of the atom
ELECTRON
negative,
orbits outside
the nucleus in
the
ELECTRON
CLOUD
PROTON
positive, also
in nucleus
NEUTRON
neutral, located in
the NUCLEUS
(center of atom)

9. Force
• The effect on a particle due to another
particle's presence.

10. The Four Fundamental Forces

11. Gravity
• Gravitational force is the attraction
between the masses of two objects.
• The larger the masses, the bigger the
attraction.
• The force of gravity can
be calculated by:
• Fg = G x m1 x m2
r2

12. Electromagnetism
• It is necessary to understand that electrical
charge (positive/negative) and magnetism
(north/south) are different aspects of the
same force -- electomagnetism.
• Oppositely charged objects, such as a
proton and an electron, attract one
another, while particles with the same
charge repel each other.

13. Strong Nuclear Force
• Protons are positively charged so they
want to repel against each other.
• The strong nuclear force is what keeps
them together

14. Weak Nuclear Force
• Little is known about the weak nuclear
force
• We know that it is responsible for the
decay of a neutron into a proton