Mass, Energy, Force

The parameters of position, speed, acceleration and time are interrelated. There are precise methods for measuring and indicating position, but in every day terms, we use direction (north, south, east, west) and distance (e.g., 185 miles) to approximate something or someone’s position. Velocity (speed) is the measure of motion from one position to another within a given period of time. Acceleration is the change of velocity within given period of time. Time is an ordering of events from beginning to end, cause to effect, at a constant rate.

Mass, in physics terms, is the resistance of an object to acceleration. We know it in layman’s terms as the amount of matter something has and how heavy it is. See weight, below.

Energy is defined in physics as “the ability to do work.” We know energy in layman’s terms as the capacity for motion.  Kinetic energy is the energy of motion. Potential energy is the energy of position. To give an example: hold a baseball above the ground. Then let it go. When it strikes the ground, it has kinetic energy KE. This is the same amount of energy it had at the moment you held it above the ground, in the form of potential energy PE. The conservation of energy states that the combination of kinetic energy and potential energy does not change in magnitude unless some other energy is introduced to the body, like another body colliding with it.

A force is action on a body that causes it to change from one energy level to another. It can cause a body to move from a complete stop to some given velocity, from a lower velocity to a higher velocity, or from a higher velocity to a lower velocity. The force on a body is equal to its mass times its acceleration.

Weight is the force on an object due to gravity. It is equal to the mass of the object times acceleration due to gravity.


Heat is the kinetic energy of the particles (atoms and molecules) within a body.

Temperature is the measure of how energetic the particles within a body are. Two or more bodies are said to be in thermal equilibrium if they are at the same temperature.

First law of thermodynamics: When energy passes, as heat, into or out from a system (that is, a single body or a group of bodies), the system’s internal energy changes by the amount brought in or taken out.

Second law of thermodynamics: Heat passes naturally from warmer bodies to cooler bodies. This principle is connected to entropy, discussed below.

Third law of thermodynamics: A body approaching a temperature of absolute zero approaches its absolute minimum energy, or ground state.

Zeroth law of thermodynamics:  If two bodies, A and B, are in thermal equilibrium with a third body C, then A is also in thermal equilibrium with B.

Electricity and Magnetism

The most basic element of electricity is charge. In nature, there are two charges: positive and negative. Opposites attract: positively-charged bodies and negatively-charged bodies attract each other, while like-charged bodies repel each other.

Electrical current is the flow of charges through a conductor. The charges come in the form of electrons, which are negatively charged.

There are two types of electrical current: direct current (DC) and alternating current (AC). Direct current maintains a single direction of flow through a conductor. Alternating current changes direction at a particular frequency, f.

Ohm’s Law

The resistance R of a conductor is the level of “opposition” the conductor has to electrical current. More resistance means less current running through the conductor.

The current I through a conductor is the measure of charges moving through the conductor within a given time period.

The voltage V across a conductor is the measure of difference of energy between each end of the conductor. (Remember that energy moves naturally from a higher-energy environment to a lower-energy environment!)

There is a relationship among R, I and V, as expressed in Ohm’s Law, which can be stated as

V = I x R

Note: this version of Ohm’s Law is an approximation that simplifies in the condition of temperature ranges in which life exists. In conditions of extreme cold or extreme heat, Ohm’s Law also becomes a function of temperature. In temperature ranges we live in, variables that are temperature-dependent cancel out.

An electric field is generated by the presence of electrical charges. An electric field is centered on a charge and extends radially away from the charge.  In the case of two charges, one positive and one negative, the field radiates from the positive to the negative. This is called an electric dipole.

A magnetic field is generated in the presence of electrical current. A static magnetic field, one does not change in time, is generated by a direct current, while a dynamic (changing in time) magnetic field is generated by alternating current.

A dynamic magnetic field generates an electric field, while a dynamic electric field generates a magnetic field. (Remember that electric fields are centered on charges, and electric current is charges in motion: they are changing in position.) An electric field and a magnetic field coming from a single source are perpendicular to each other. Together they are known as an electromagnetic field.


Matter is made up of atoms. Atoms are comprised of a nucleus at the center and one or more electrons in orbit around it. Atomic nuclei are made up of two other particles: protons and neutrons. Electrons are negatively charged, protons are positively charged, and neutrons have no electrical charge.

A substance comprised of only a single atom is known as an element. An element’s atomic number is the number of protons in its nucleus, while its atomic mass is the related to the number of both protons and neutrons in its nucleus. The number of protons in an atom’s nucleus is the dominant factor in how many electrons will be in orbit around the nucleus.

Electrons, while have charges equal in magnitude to those of protons, are much smaller and lighter than protons.

Electrons are responsible for the chemical behavior of elements. They are what form atomic bonds to form compounds.

Protons, neutrons and electrons are particles in a larger group known as fermions. Fermions also include quarks and leptons. Quarks are a type of elementary particle, that is, they cannot be broken down into smaller particles. They join together larger particles called hadrons. Protons and neutrons are classified as hadrons.