Slovak Physics Olympiad Cat A key terms

The vector pointing from an object's initial position to its current position, with magnitude and direction. It differs from distance travelled, which is a scalar counting total path length regardless of direction.

The rate of change of displacement with time, a vector quantity. Average velocity divides total displacement by elapsed time, while instantaneous velocity is the limit of that ratio as the time interval shrinks to zero.

The rate of change of velocity with time, a vector quantity. An object accelerates when its speed changes, its direction changes, or both; for constant acceleration, motion follows simple kinematic equations.

The net force on a body equals the rate of change of its momentum; for constant mass this reduces to force equals mass times acceleration. It links causes of motion (forces) to the resulting acceleration vector.

The product of a body's mass and its velocity, a vector quantity. In an isolated system the total momentum stays constant, which makes it a powerful tool for analysing collisions and explosions.

In an isolated system the total energy remains constant, though it may change form between kinetic, potential, thermal and other types. It constrains motion and is often used together with momentum conservation to solve mechanics problems.

The energy transferred to a body by a force acting along its displacement, computed as the scalar product of force and displacement. Only the component of force along the motion does work.

Energy stored because of a body's position within a conservative force field, such as gravity or a spring. It is defined relative to a chosen reference point and converts to kinetic energy as the body moves.

The point representing the mass-weighted average position of a body or system, moving as if all external forces acted there. For uniform symmetric bodies it coincides with the geometric centre.

The turning effect of a force about an axis, equal to the product of the force and its perpendicular distance from the axis. It changes a body's angular momentum and, in statics, torques must balance for equilibrium.

A measure of a body's resistance to angular acceleration about a given axis, equal to the sum of each mass element times its squared distance from the axis. It plays the role in rotation that mass plays in translation.

Three empirical rules describing planetary motion: orbits are ellipses with the Sun at one focus; equal areas are swept in equal times; and the square of the orbital period is proportional to the cube of the semi-major axis.

The universal constant G appearing in Newton's law of gravitation, with value about 6.67 times ten to the minus eleven newton metre squared per kilogram squared. It sets the strength of gravitational attraction between masses.

The minimum speed needed at a given distance from a massive body for an object to escape its gravitational pull without further propulsion. For Earth's surface it is about 11.2 kilometres per second.

A relation for steady ideal fluid flow stating that pressure plus kinetic energy density plus gravitational potential energy density is constant along a streamline. It explains how faster flow corresponds to lower pressure.

For an incompressible fluid in steady flow, the product of cross-sectional area and flow speed is constant along a pipe. It expresses conservation of mass for fluids.

The upward force exerted by a fluid on an immersed or floating body, equal to the weight of the displaced fluid (Archimedes' principle). Floating occurs when this force balances the body's weight.

The equation of state relating pressure, volume, temperature and amount of gas as pressure times volume equals amount times the universal gas constant times absolute temperature. It applies to gases at low density.

Temperature measured on the Kelvin scale, starting at absolute zero where molecular thermal motion is minimal. It must be used in gas laws and thermodynamic formulas because those relations are proportional to it.

A model explaining gas properties from the random motion of many small particles colliding elastically. It derives pressure and temperature from average molecular speed and connects temperature to mean kinetic energy.

The change in internal energy of a system equals heat added to it minus work done by it. It is the energy-conservation statement for thermal processes involving heat and work.

The total kinetic and potential energy of the particles making up a thermodynamic system, depending on its state. For an ideal gas it depends only on temperature.

The heat needed to raise the temperature of one kilogram of a substance by one kelvin. It determines how much energy a body absorbs for a given temperature change.

The energy absorbed or released per unit mass during a phase change at constant temperature, such as melting or boiling. It breaks or forms bonds between molecules without changing their average kinetic energy.

A thermodynamic change in which no heat is exchanged with the surroundings, so work done comes entirely from internal energy. Rapid compression or expansion of a gas is approximately adiabatic.

Oscillation in which the restoring force is proportional to displacement and directed toward equilibrium, producing sinusoidal motion. Its period is independent of amplitude and set by mass and stiffness.

A large amplitude response that occurs when an oscillating system is driven at a frequency matching one of its natural frequencies. Energy transfer from the driver is then maximal.

The speed at which a disturbance pattern travels through a medium, equal to frequency times wavelength. It is set by the medium's properties, not by the source's amplitude or frequency.

The distance between two consecutive points in phase on a wave, such as crest to crest. It relates to frequency and wave speed through the wave equation.

The superposition of two or more waves, producing regions of reinforced amplitude (constructive) or reduced amplitude (destructive). It requires coherent sources for a stable pattern.

A wave pattern formed by two identical waves travelling in opposite directions, with fixed nodes and antinodes. It stores energy without net transport and underlies vibration modes of strings and pipes.

The spreading of waves around obstacles and through openings, becoming pronounced when the obstacle or slit size is comparable to the wavelength. It limits the resolution of optical instruments.

A vector field describing the force per unit positive charge at each point in space, created by charges and changing with time when charges accelerate. Field lines point away from positive and toward negative charge.

The electric potential energy per unit positive charge at a point, a scalar measured in volts relative to a reference. The field points from higher to lower potential.

The electrostatic force between two point charges is proportional to the product of the charges and inversely proportional to the square of their separation, acting along the line joining them. It is the electrostatic analogue of gravitation.

The charge stored on a conductor per unit potential difference applied, measured in farads. It depends on geometry and the dielectric between the plates.

The generation of an electromotive force in a conductor when the magnetic flux through it changes, described by Faraday's law. The induced current opposes the change according to Lenz's law.

The measure of magnetic field passing through a surface, computed as the field's component perpendicular to the surface times its area, in webers. A changing flux drives induction.

Two rules for circuits: the sum of currents into a junction is zero (charge conservation), and the sum of potential differences around any closed loop is zero (energy conservation). They solve complex DC and AC networks.

For a conductor at constant temperature, current is proportional to potential difference across it, with resistance as the constant of proportionality. It defines resistance and fails for non-ohmic devices.

The change in direction of a wave when it crosses a boundary between media of different wave speeds, governed by Snell's law. It also involves partial reflection and possible total internal reflection.

The complete reflection of light at a boundary when it travels from a denser to a less dense medium at an angle beyond the critical angle. It is used in optical fibres and prisms.

The relation linking object distance, image distance and focal length for a thin lens, with inverse distances. It predicts image position and, with magnification, image size and orientation.

The restriction of a transverse wave's oscillation to a particular plane or pattern. Light can be polarized by reflection, scattering, or passing through certain filters.

The relativistic effect in which a clock moving relative to an observer ticks more slowly than one at rest with that observer, described by the Lorentz factor. It becomes significant as speeds approach the speed of light.

The factor depending on relative speed that scales time intervals, lengths and relativistic momentum, equal to one over the square root of one minus speed squared over light speed squared. It equals one at rest and grows without bound near light speed.

The principle that mass is a form of energy, related by energy equals mass times the speed of light squared. It explains energy release in nuclear reactions and particle creation.

The emission of electrons from a metal surface when light of sufficiently high frequency strikes it. It reveals that light delivers energy in discrete quanta called photons.

A quantum of electromagnetic radiation carrying energy proportional to its frequency and momentum proportional to its wavenumber. It is the particle-like aspect of light.

The minimum energy needed to remove an electron from the surface of a material. In the photoelectric effect it sets the threshold frequency of incident light.

The spontaneous transformation of unstable nuclei into other nuclei, emitting alpha, beta or gamma radiation. The number of undecayed nuclei falls exponentially with a characteristic half-life.

The time after which half of the radioactive nuclei in a sample have decayed. It is constant for a given isotope and independent of the sample's initial size.

A consistent deviation of measurements from the true value in one direction, caused by faulty instruments, calibration or method. Repeating measurements does not reduce it, unlike random error.

Scatter in repeated measurements above and below the true value, arising from unpredictable fluctuations. It can be reduced by averaging many readings.

A quantitative estimate of the range within which the true value of a measurement probably lies. It is propagated through calculations to give the uncertainty of a derived result.

The digits in a reported number that carry meaningful information about its precision. Results should be quoted with no more precision than the least precise input justifies.

The technique of transforming measured variables so that data plot as a straight line, allowing slope and intercept to yield physical constants. It makes relationships easy to verify and quantify.