| Glossary | ||||||||||||||
| momentum
— vector equal to the product of velocity and mass. Momentum has units of kg m/s (kilogram meter per second) or N s (newton second). net force — combination of all the forces that act on a body. neutron — neutral subatomic particle with zero electric charge that has a mass of 1.675×10−27 kg. newton (N) — SI unit of force that is equivalent to 1 kg m/s2. A one newton net force applied to a one kilogram mass will accelerate the mass by 1 m/s2. Newton’s first law of motion — an object at rest remains at rest, and an object in motion continues with constant velocity, unless acted on by a net force. Newton’s law of cooling — rate of heat flow is approximately proportional to the temperature difference. Newton’s second law of motion — acceleration of an object is proportional to the net force acting on it and inversely proportional to its mass. Newton’s third law of motion — whenever one object exerts a force on another object, the second object exerts an equal and opposite force on the first object. node — stationary point on a standing wave. A point of minimum or zero amplitude. normal — line that is perpendicular to another line or surface. normal force — force perpendicular to a surface. Typically created where objects touch other objects or surfaces, such as floors or walls. nuclear energy — type of energy created by reactions in the atomic nucleus. nuclear reaction — process in which the nucleus of an element is changed into a different isotope of that element or a different element altogether. nuclear waste — unwanted byproducts of nuclear reactions that are radioactive, have long half-lives, and must be disposed in safe, long-term storage. | nucleus
— tiny dense core of an atom that contains all the protons and neutrons, measuring approximately 1/10,000 of the diameter of the atom. object distance — distance between the object and the optical element (such as a mirror or lens). objectivity — description only of what has actually occurred without opinion, interpretation, or exaggeration. ohm (Ω) — unit of electrical resistance. A resistance of one ohm (1 Ω) means a current of one amp will flow if a voltage of one volt is applied. Named in honor of Georg Simon Ohm. Ohm’s law — current in an electric circuit is proportional to the voltage applied and inversely proportional to the resistance, or I = V/R. Named in honor of Georg Simon Ohm. opaque — material that allows no light to pass through it. open circuit — electric circuit with a break that prevents electricity from flowing through it. The opposite of a closed circuit. open system — system on which outside influences can act, such that matter or energy can be added or removed from the system. optical axis — (1) for a mirror, a line perpendicular to the surface of a mirror that joins its focal point and center of curvature. (2) for a lens, a line connecting the centers of curvature of the surfaces of the lens. optical fibers — thin, transparent, and flexible tube, usually made of glass or plastic, that transmits light. Often used for communications technology. orbit — regular, curved path one object travels around another object that is maintained by an attractive force such as gravity. Usually refers to the gravitationally determined path of a planet or satellite around another, larger body. orbital period — time it takes a satellite to complete one orbit with respect to the fixed stars or celestial sphere. Earth’s orbital period is 365.24 days. | |||||||||||||
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