Lesson 10 Fundamental Forces

The variety of phenomena in the universe can be described by four forces: the strong nuclear force, the weak nuclear force, the electrical force, and the force of gravity. These are the four fundamental forces of nature, and every piece of matter is subject to these forces.

The first two fundamental forces of stong nuclear force and weak nuclear force are located in the nucleous of an atom.

The strong nuclear force is represented by neutrons in the nucleous that overcome the natural repulsion of protons, and bring the protons together. The power released in nuclear reactions is also due to the strong nuclear force. Reactions such as this are present on the sun.

The weak nuclear force has subtle effects in the nucleous and can be represented by the death of stars and the decay of radioactive isotopes. Below is a video that explains the two forces in great detail:



Gravity accelerates mass and reaches out over the bounds of the entire universe. Gravity is explained in terms of force which is measured in newtons.

In 1798, Henry Cavendish weighed the earth and was able to measure the constant in Newton's Law of Universal Gravitation (the force between any two objects):

F = ma                                                  F = mg

F = kg (m/s^2)                                     F = mm(e)
                                                                     r(e)^2

   = N                                                    Gm(e) = gr(e)^2         9.800 m/s^2

                                                             Gm(e) = (9.800 m/s^2) r(e)^2

                                                              r = (6.378 x 10^6 m)^2

                                                              Gm(e) = 3.986 x 10^14 Nm^2/kg

After finding Gm(e), Cavendish was able to weigh the earth using a device depicted below:

In this device, the gravitational force between the two masses causes the bar to twist. By timing the beam's oscillation, Cavendish measured the inertia of the beam with the two balls. The attraction to the other balls could be measured by deflection of the beam and Cavendish found G to be about 6.67 x 10^-11. Cavendish then took Gm(e) and divided it by G to find that the mass of the earth was 5.976 x 10^24 kg.

In regards to the force of electricity, everything is at equilibrium. For example, protons have a positive electrical charge, neutrons have a neutral electrical charge, and electrons have a negative electrical charge. However, all elements are stable with an equal amount of protons and electrons to produce an overall neutral charge.

The force of electricity:

F(e) = k(e) q1q2 r^
                     r^2
where k is the electrical constant, q1 and q2 are the charges, and r^2 is the square of the distance between two objects.

Spring action, friction and viscosity are all electrical forces. A metal spring exhibits electrical force because positively charged metal ions are glued by negatively charged electrons, and as the positive metal ions pull the spring apart, the negatively charged electrons pull the spring back together. Friction is the binding of positive and negative forces as they interact, and viscosity exhibits the interaction of negative and positive forces.

All of the forces mentioned above can be observed in ion and proton accelerators, which are commonly used to study the origns of stars. Friction, gravity, strong nuclear force, weak nuclear force, electricity are all present in the accelerator as the ion passes through a charged gas and looses electrons.

In conclusion, the four fundamental forces have similar theorems, thus, scientists believe there is a single force that explains all. This is known as the Single Unified Theory, however research still continues to this day.