average — value obtained from a set of measurements by adding up all their measurement values and dividing by the total number of measurements

average velocity — distance or displacement an object travels divided by the time taken, regardless of any variations in velocity during the time interval.

Avogadro’s number — 6.022×1023 particles, the number of particles in one mole.

axis — (1) imaginary straight line about which an object rotates;
(2) one of the reference lines used to depict a coordinate system.


bar graph — a graph in which the height or length of columns or bars represent the values of data

battery — device that transforms or converts chemical energy into electrical energy or electric current. A battery’s voltage, or potential difference, is measured in volts (V).

beats — pulsations of sound resulting from the superposition of two waves of different frequencies. The beat frequency is the difference in frequency between the two waves.

Bernoulli’s equation — expression of energy conservation along a streamline for a frictionless fluid. Often expressed as ρgh + ½mv2 + P = constant.

beta decay — radioactive decay in which a neutron in the nucleus of an atom spontaneously converts into a proton and an electron. The proton remains in the nucleus, increasing the atom’s atomic number by one, while the energetic electron is emitted as a beta particle.

binding energy — net energy that must be supplied to overcome the strong nuclear force in order to split an atomic nucleus into its constituent particles.

biomechanics — study of the motion of various parts of the human body (or other living organisms).

black hole — gravitational singularity predicted by general relativity.

blackbody — absorbs 100% of the electromagnetic radiation (i.e., thermal radiation) incident upon its surface.

block and tackle — system of pulleys that changes the magnitude of the input force, not just its direction. Often used in sailing.

Bohr model — model of the hydrogen atom, proposed by Danish physicist Niels Bohr, where the electron moves in circular orbits only at discrete or quantized radii from the nucleus.

Boltzmann’s constant — constant describing the conversion between microscopic thermal energy per particle and macroscopic temperature. The value of Boltzmann’s constant is kB = 1.38×10−23 J/K.

Boyle’s law — for a gas at constant temperature, the change in pressure is inversely proportional to the change in volume. Often written P1V1 = P2V2.

brittle — material property describing the tendency to break before deforming. Brittle is the opposite of elastic.

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