Lesson 11 Gravity, Electricity, and Magnetism

Three values govern the nature of the world. These values include: the force of gravity, the speed of light, and the electric charge of an electron. The Gravitational constant (G) is equivalent to 6.7 x 10^-8 dyne cm^2/g^2, a value so small that scientists do not have the appropriate technology to measure the force exactly. The speed of light (c) is equivalent to 3 x 10^10 cm/sec, and serves as a tool to measure the vastness of space. In other words, distance in space is measured by light-years or the distance light travels in one year. The electric charge of an electron (e) is equivalent to 4.7 x 10^-10 esu. These values were not discovered outright by a single physicist or scientist. Instead, numerous physicists contributed to these findings:

In 1675, Ole Romer observed the delay of the eclipse of Jupiter's satelites in order to calculate the velocity of light.

In 1849, Hippolyte Fizeau used rotating wheels to measure the speed of light through air and water.

In 1850, Jean Foucault named and improved the gyroscope and discovered the speed of light with a series of rotating mirrors.

In 1926, Albert Michelson measured the time it took light to travel from two large peaks (Wilson/San Antonio) in Los Angeles. Michelson found that it took .0001 sec for light to travel from one peak to the other. These peaks were roughly 30 km apart. Therefore speed is equal to distance/time, and the speed of light is about 3 x 10 ^8 m/s. Below is a video displaying how the speed of light can be measured using a chocolate bar and a microwave:

Another distinct force is magnestism:

F(m) = k(m) p1p2r^
                         r^2

Magnetic poles, represented by p1 and p2, are always in pairs that are equal and opposite. This equation is strikingly similar to the equation of the force of electricity. In 1820, Hans Christian Oersted discovered this relationship between electricty and magnetism known as electromagnetism. Oersted found that a compass needle would deflect from magnetic north when an electric current from a battery was switched on and off. Oersted first believed that magnetic effects were produce from all sides of the wire, but after future investigation, he discovered that an electric current produces a circular magnetic field as it flows through a wire. Below is an example of his experiment:



Gravity:
G = 6.7 x 10^-11 Nm^2/kg^2

Electricity:
K(e) = 9 x 10^9 Nm^2/e^2 (coulombs)

Magnetism:
K(m) = 1 x 10^-7 Ns^2/e^2 (amperes or coulombs per second)

Due to the relationship of electromagnestism, James Clark Maxwell discovered that magnestism and electricty were not independent:

K(e)/K(m) = 9 x 10^9 Nm^2/e^2
                     1 x 10^-7 Ns^2/e^2

                   = 9 x 10^16 m^2/s^2
This is a squared speed due to squared distance over a squared time, therefore the square root must be taken in order to obtain the speed:

                     =3 x 10^8 m/s  or the speed of light

Samuel Morse, the creator of the telegraph, commented on the complexity of the construction of a telegraph wire across the Atlantic Ocean. Such complex tasks compare to the equally complex task of discovering the relationships between all motion, matter, and force, the study of physics.