Forces Notes Inertia Inertia is a property of matter where an object at rest will stay at rest and an object in motion will remain in motion unless acted upon by an outside force. But, what is force? Force A force is an agent that causes or opposes changes in motion. There are four fundamental forces in nature: 1) Gravitational 2) Electromagnetic 3) Strong Nuclear 4) Weak Nuclear These four forces are part of the atomic building blocks of matter. They are the forces from which all other forces are derived. Gravitational Force Gravitational force was the first to be recognized. It is a long-range force proportional to the mass of the objects. It is the dominant force that governs the motions of planets and all celestial processes. All objects exert gravitational forces on all other objects. Electromagnetic Force For centuries electric and magnetic forces were thought to be distinct. James Maxwell recognized they were two components of the same force. It is a long range force that can also act at very short distances. EM forces are responsible for chemical bonding and interactions between atoms and molecules. Therefore, they play an important role in the physical and chemical properties of matter. Nuclear Forces The strong nuclear and weak nuclear forces were discovered early in the 20th century during the development of quantum theories of the atom. They act over very short distances, comparable to the size of protons and neutrons. They help hold the nucleus of an atom together and play and important role in several types of nuclear decay. Classification of Forces Non-contact forces act at a distance and do not require physical contact to transmit the force. The two non-contact forces are gravity and electromagnetism. Gravity displays only attractive force, while EM displays both attractive and repulsive force. Contact forces (mechanical forces) are transmitted only by physical contact between objects. They are derived from the electromagnetic forces among particles of matter. Usually these forces are pushes, pulls, twists, and/or friction Measuring Force Instruments used to measure force include spring scales, force plate, pressure gauges, etc. The SI unit used for force is the Newton (N) which is a kgm/s2 Gravity (Fg) the force between any two objects with mass. (Usually the force between the Earth and an object.) Fg=mg g=10 N/kg for objects near the Earth's Surface.