The Fundamental Forces
- Most all of the ordinary matter in the universe is made up of protons, neutrons,
- Protons are relatively massive particles which carry a
positive electrical charge.
- Electrons are low-mass particles which carry a negative
- Neutrons have the same mass as protons, but they carry no
- Surprisingly only a small fraction of the matter in the universe is
in this form. Most of the matter is in an unknown form that we detect
only from its gravitational influence on the ordinary matter!
- The fundamental forces of nature determine how these particles are
arranged and how they interact with one another.
- Gravity -- An attractive force between
any two masses.
- It holds stars, galaxies, and planetary systems together
- Electromagnetism -- A force between electrical
charges (i.e. between protons and protons or protons and electrons)
- Like charges repel. Opposite charges attract.
- It holds atoms (protons and electrons) together.
- Aside: Atoms are even more empty than the Solar System. Virtually all of any ``solid" object is empty space. Squeeze all of the empty space out of a human being and you will be left with a lump of material 10 micrometers in size - 1/10th the width of a human hair!
- It bonds atoms together to form molecules, liquids,
- Electromagnetism also is responsible for "light".
- Strong Nuclear Force -- An attractive force between
protons and protons or protons and neutrons.
- Unlike the above two forces, it operates only over
distances about the size of an atomic nucleus (femtometers = 10-15 meters) like nuclear velcro.
- It binds atomic nuclei (protons and neutrons) together.
- It is so strong that it can overcome the electromagnetic
repulsion of proton vs. proton.
- The various combinations of protons and neutrons allowed by
nature give rise to the various elements and their isotopes.
- The number of protons in an
atomic nucleus determine the elemental identity of an atom.
- For example all oxygen atoms of 8 protons while all carbon atoms have 6 protons.
- When forces act they do work and release energy. Stars tap the
strong nuclear force via thermonuclear fusion of hydrogen into helium
in their cores, permitting
stars like the Sun to shine for billions of years.
Back to Spectral Lines
Revised February 20, 2002