PURE PHYSICS DEFINITIONS

PURE PHYSICS DEFINITIONS Physical quantity A physical quantity is a quantity that can be measured. It consists of a numerical magnitude and a unit . Period The period of a simple pendulum is the time taken for one complete oscillation . Scalar quantities Scalar quantities are physical quantities that have only magnitude . Vector quantities Vector quantities are physical quantities that have both magnitude and direction . Distance The total length covered by a moving object regardless of the direction of motion. Displacement The distance measured in a straight line in a specified direction. Speed Distance travelled per unit time Velocity Rate of change of displacement Acceleration Rate of change of velocity Uniform acceleration Constant rate of change of velocity Gradient of d-t graph Gives the velocity of the object Gradient of v-t graph Gives the acceleration of the object Area under v-t graph Gives the displacement of the object

Mass Measure of the amount of matter in a body . Weight Gravitational force acting on an object that has mass. Gravitational field A region in which a mass experiences a force due to gravitational attraction. Gravitational field strength, g Gravitational force per unit mass placed at that point. N1L Newton’s First Law of Motion states that every object will continue in its state or uniform motion in a straight line unless a resultant force acts on it. Inertia Reluctance of the object to change its state of rest or motion, due to its mass . N2L Newton’s Second Law of Motion states that when a resultant force acts on an object of a constant mass, the object will accelerate in the direction of the resultant force. N3L Newton’s Third Law of Motion states that if body A exerts a force on body B, then body B will exert an equal and 𝐹 𝐴𝐵 opposite force on body A. 𝐹 𝐵𝐴 Friction Contact force that opposes or tends to oppose motion between surfaces in contact . Moment of a force, torque The moment of a force about a pivot is the product of the force F and the perpendicular distance d from the pivot to the line of action of the force . Principle of moments When a body is in equilibrium , the sum of clockwise moments about a pivot is equal to the sum of anticlockwise moments about the same pivot .

Centre of gravity Imaginary point where the entire weight of the object seems to act . Stability of an object Measure of its ability to return to its original position. Pressure Force acting per unit area Pascal’s law If a pressure is applied to an enclosed liquid, the pressure is transmitted to all other parts of the liquid undiminished. Density Mass per unit volume Principle of conservation of energy Energy cannot be created or destroyed . Energy can be transferred from one store to another . The total energy of an isolated system is constant . Work done Product of the force and the distance moved by the object in the direction of the force. Power Work done or energy transferred per unit time. Kinetic particle model of matter Made up of tiny particles that are in continuous motion. Temperature Temperature rises with the average kinetic energy of the particles in a body and vice versa. Thermal equilibrium State in which two or more objects have the same temperature and that there is no net transfer of energy between them .

Conduction Process of energy transfer where energy is transferred through the passing on of vibrational motion from one particle to another . Convection Process of energy transfer where energy is transferred by means of convection currents of a fluid (liquid or gas), due to a difference in density Radiation Process of energy transfer where energy is transferred by electromagnetic waves. It does not require a medium. Internal energy Internal energy is an energy store that is made up of the total kinetic energy associated with the random motion of the particles and the total potential energy between the particles in the system. Heat capacity Heat capacity of an object is the change of its internal energy per unit change in its temperature. Specific heat capacity Specific heat capacity of a material is the change of its internal energy per unit mass for each unit change in its temperature. Latent heat Energy released or absorbed to change the state of a substance, at constant temperature. Latent heat of fusion Amount of energy transferred to change a substance between the solid and liquid states, at constant temperature. Specific latent heat of fusion Amount of energy transferred per unit mass of a substance to change between the solid and liquid states, at constant temperature.

Latent heat of vaporisation Amount of energy transferred to change a substance between the liquid and gaseous states, at constant temperature. Specific latent heat of vaporisation Amount of energy transferred per unit mass of a substance to change between the liquid and gaseous states, at constant temperature. Wave Disturbance that propagates through space, transferring energy with it but not matter. Transverse wave Direction of vibration that is perpendicular to the direction of wave travel. Longitudinal wave Direction of vibration that is parallel to the direction of wave travel. Wavefront Imaginary line joining all adjacent points that are in phase . Infrasound Frequencies below 20 Hz Ultrasound Frequencies above the upper limit of the human range of audibility. Frequencies above 20 000 Hz / 20 kHz. Refraction Bending of light as it passes from one optical medium to another. Refractive index Ratio of the speed of light in a vacuum to the speed of light in that medium. Principle of reversibility of light rays Regardless of how many times a light ray has been reflected or refracted, it will follow the same path when its direction is reversed.

Critical angle Angle of incidence in an optically denser medium for which the angle of refraction in the less dense medium is 90°. Total internal reflection Complete reflection of a light ray in an optically denser medium at the boundary with an optically less dense medium. Electric field A region in which an electric charge experiences an electric force. Electric current Rate of flow of electric charge. Electromotive force Work done by the source in driving a unit charge around a complete circuit. Potential difference Potential difference across a component in a circuit is the work done per unit charge in driving charges through the component. Resistance Ratio of the potential difference across it to the current flowing through it. Potential divider Voltage divider, which makes use of the voltage drop across resistors in series to divide voltage. Induction Takes place when a magnetic material is placed close to a strong magnet or within a current-carrying solenoid. Magnetic