FORCES are any push or pull. Forces accelerate objects.
Gravity is the fundamental force of attraction that ALL objects with mass have for each other. Like the electromagnetic force, gravity has effectively infinite range and obeys the inverse-square law. At the atomic level, where masses are very small, the force of gravity is negligible, but for objects that have very large masses such as planets, stars, and galaxies, gravity is a predominant force, and it plays an important role in theories of the structure of the universe. GRAVITY AMERICAN HERITAGE DICTIONARY
APPLIED forces are forces applied to one object by another object.
ACTION AT A DISTANCE VS. CONTACT FORCES Action-at-a- distance forces are those types of forces that result even when the two interacting objects are not in physical contact with each other, yet are able to exert a push or pull despite their physical separation. Examples of action-at-a-distance forces include gravitational forces. For example, the sun and planets exert a gravitational pull on each other despite their large spatial separation. Even when your feet leave the earth and you are no longer in physical contact with the earth, there is a gravitational pull between you and the Earth. Electric forces are action-at-a- distance forces. For example, the protons in the nucleus of an atom and the electrons outside the nucleus experience an electrical pull towards each other despite their small spatial separation. And magnetic forces are action-at-a-distance forces. For example, two magnets can exert a magnetic pull on each other even when separated by a distance of a few centimeters. Contact Forces – friction, tension, normal, air resistance, applied, spring Action-at-a-Distance Forces – gravity, electrical, magnetic Force is a quantity that is measured using the standard metric unit known as the Newton. A Newton is abbreviated by an "N." To say "10.0 N" means 10.0 Newton of force. One Newton is the amount of force required to give a 1-kg mass an acceleration of 1 m/s/s. Physicsclassroom.com
4 FUNDAMENTAL FORCES As you sit in front of your computer reading this article, you may be unaware of the many forces acting upon you. A force is defined as a push or pull that changes an object's state of motion or causes the object to deform. Newton defined a force as anything that caused an object to accelerate -- F = ma, where F is force, m is mass and a is acceleration. The familiar force of gravity pulls you down into your seat, toward the Earth's center. You feel it as your weight. Why don't you fall through your seat? Well, another force, electromagnetism, holds the atoms of your seat together, preventing your atoms from intruding on those of your seat. Electromagnetic interactions in your computer monitor are also responsible for generating light that allows you to read the screen. Gravity and electromagnetism are just two of the four fundamental forces of nature, specifically two that you can observe every day. What are the other two, and how do they affect you if you can't see them? The remaining two forces work at the atomic level, which we never feel, despite being made of atoms. The strong force holds the nucleus together. Lastly, the weak force is responsible for radioactive decay, specifically, beta decay where a neutron within the nucleus changes into a proton and an electron, which is ejected from the nucleus. Without these fundamental forces, you and all the other matter in the universe would fall apart and float away. Craig Freudenrich, Ph.D.
FORCE FIELDS occur for action at a distance forces – gravity and electromagnetic forces
INTERNAL VS. EXTERNAL FORCES physicsclassroom.com Forces can be categorized as internal forces or external forces. There are many sophisticated and worthy ways of explaining and distinguishing between internal and external forces. Many of these ways are commonly discussed at great length in physics textbooks - particularly college-level physics textbooks. For our purposes, we will simply say that external forces include applied force, normal force, tension force, friction force, and air resistance force. And for our purposes, the internal forces include the gravity forces, magnetic force, electrical force, and spring force. While this is a simplistic approach, it is an approach that will serve us well in our introduction to physics. The importance of categorizing a force as being either internal or external is related to the ability of that type of force to change an object's total mechanical energy when it does work upon an object. When net work is done upon an object by an external force, the total mechanical energy (KE + PE) of that object is changed. If the work is positive work, then the object will gain energy. If the work is negative work, then the object will lose energy. The gain or loss in energy can be in the form of potential energy, kinetic energy, or both. Under such circumstances, the work that is done will be equal to the change in mechanical energy of the object. This principle will be discussed in great detail later in this lesson. Because external forces are capable of changing the total mechanical energy of an object, they are sometimes referred to as nonconservative forces. When the only type of force doing net work upon an object is an internal force (for example, gravitational and spring forces), the total mechanical energy (KE + PE) of that object remains constant. In such cases, the object's energy changes form. For example, as an object is "forced" from a high elevation to a lower elevation by gravity, some of the potential energy of that object is transformed into kinetic energy. Yet, the sum of the kinetic and potential energies remains constant. This is referred to as energy conservation and will be discussed in detail later in this lesson. When the only forces doing work are internal forces, energy changes forms - from kinetic to potential (or vice versa); yet the total amount of mechanical is conserved. Because internal forces are capable of changing the form of energy without changing the total amount of mechanical energy, they are sometimes referred to as conservative forces.
NEWTON = THE METRIC UNIT OF FORCE (N) A force is a push or a pull, or more generally anything that can change an object’s speed or direction of motion. A force is required to start a car moving, to slow down a baseball player sliding in to home base, or to makean airplane turn. (Forces may fail to change an object’s motion if they are canceled by other forces, e.g. the force of gravity pulling you down right now is being canceled by the force of the chair pushing up on you.) The metric unit of force is the Newton, defined as the force which, if applied for one second, will cause a 1-kilogram object starting from rest to reach a speed of 1 m/s. ALL FORCES ARE MEASURED IN NEWTONS www.faqs.org/docs/Newtonian
ELECTROMAGNETIC FORCES An electromagnetic force is a physics concept that refers to a particular force, or influence, that affects charged particles. These particles may be positively or negatively charged. The force, which is carried via photons, is responsible for holding electrons and protons together in an atom, and holding atoms together in a molecule. We encounter electromagnetic forces daily; they are the reason behind attraction and repulsion of magnets and electrical charges, and they factor in chemical reactions as well.
Work is a Result of Force by Ron Kurtus (revised 12 October 2008) Work is defined as the result of applying a force to an object in order to move it a certain distance. In other words, work equals force times distance. Work is always against some resistance.