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| power
— rate at which work is done or energy is transferred. The units of power are watts (W). One watt is one joule per second. precession — wobbling of a spinning object, such that the object’s axis of rotation traces out an imaginary cone. precision — degree of mutual agreement among a series of measurements of the same quantity. pressure — force per unit area. SI units are pascals (Pa) and 1 Pa = 1 N/m2. English units are pounds per square inch (lb/in2) or psi. prism — optical device, usually a triangular block of transparent material such as glass, that separates white light into its constituent colors through dispersion. projectile — moving body traveling only under the influence of gravity. proton — positively charged subatomic particle with a mass of 1.673×10−27 kg and charge of +1.602×10−19 C. pulley — wheel that acts as a lever to change the direction of an input force. One of six types of simple machines. PV diagram — graph of pressure P as the vertical axis and volume V as the horizontal axis on which thermodynamic processes can be analyzed. The area enclosed by a process on a PV diagram is the work done by the system. quadratic — equation containing a dependence of one variable on another variable raised to the second power. For example, an equation is quadratic in x when it includes terms involving x2. qualitative — description or explanation that does not involve or predict numerical values. quantitative — description or explanation that involves or predicts numerical values. quantized — concept applying to the atomic scale where physical quantities, such as energy, are permitted only to take discrete values. Examples: the energy of a photon of light is quantized as E = hf; and the orbits of an electron in Bohr’s model of the hydrogen atom are quantized as n = 1, 2, 3,... | quantum number
— dimensionless value that specifies a state in the quantum theory. The quantum number is an integer for the orbits of the electron, but can take half-integer values for other quantum states such as the spin of the electron. quantum physics — field of science that explains physical phenomena at atomic scales. The quantum theory is notable in describing many quantities as having only discrete, not continuous, values called quanta. In quantum physics, light and elementary particles exhibit both particle and wave phenomena. radian (rad) — angle that has an arc length that is equal to its radius. One radian is equivalent to approximately 57.3°. One full circle is 360 degrees or 2π radians. It is not necessary to include “rad” when expressing an angle in radians because all angles are assumed to be in radians unless otherwise noted (e.g., when given in degrees). radiant energy — energy transferred by electromagnetic waves. Also called electromagnetic energy. radiation — (1) the process of emitting electromagnetic, or radiation, energy; (2) the particles and energies emitted from radioactive substances. radio waves — longest wavelength region of the electromagnetic spectrum. radioactive decay — spontaneous, partial disintegration of a nucleus that is accompanied by the release of an energetic particle or radiation. ramp — inclined surface or plane used for elevating objects. One of six types of simple machines. ramp coordinates — coordinate system where one axis is parallel to the slope of a ramp or inclined plane. Since motion down an inclined plane is parallel to the plane, ramp coordinates are the natural axes to use for the equations of motion. range — horizontal distance a projectile travels between its launching point and the point where it hits the ground. ray diagram — diagram showing how the direction of light rays changes as they are reflected and/or refracted by optical devices. | |||||||||||||
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