1. Modern Physics Four Forces of nature

2. Scientists describe all of nature with only four forces. Gravitational force Weak Nuclear force Electromagnetic force Strong nuclear force It is important to note that scientists do not know why these forces exist or what causes them. We only observe their effects and propose they are there.

3. Electromagnetic Force The force is the attraction between protons (positive) and electrons (negative). Electrons are bound to the nucleus by electromagnetic forces.  The momentum of the electron causes it to move around the nucleus rather than falling straight in.

4. Strong Nuclear Force Holds the nucleus of an atom together Attracts neutrons and protons to each other, otherwise the positively charged protons would repel each other.

5. Weak Nuclear Force Causes a neutron to break into a proton and an electron producing a new element Weaker than both the electric force and the strong nuclear force. Causes radioactive decay Only occurs at the subatomic level The force of gravity causes objects to be attracted to each other  Every process we know in the universe can be explained in terms of these fundamental forces.