Physics Terms To Know

Displacement (s)

Distance traveled in a particular direction (change in position).

Velocity (u, v)

Rate of change of displacement.

Speed (u, v)

Rate of change of distance.

Acceleration (a)

Rate of change of velocity.

Newton’s 1st Law of Motion

An object at rest remains at rest and an object in motion remains in motion at a constant speed in a straight line unless acted on by an unbalanced force.

Newton’s 2nd Law of Motion

An unbalanced force will cause an object to accelerate in the direction of the net force. The acceleration of the object is proportional to the net force and inversely proportional to its mass.

Newton’s 3rd Law of Motion

When two bodies A and B interact (push or pull), the force that A exerts on B is equal and opposite to the force that B exerts on A. For every force, there is an equal and opposite reaction.

Translational Equilibrium

Net force acting on a body is 0.

Linear Momentum (p)

Product of mass and velocity.

Impulse (J)

Change in momentum.

Law of Conservation of Linear Momentum

The total momentum of an isolated system (no external forces) remains constant.

Work (W)

The product of a force on an object and the displacement of the object in the direction of the force.

Kinetic Energy (E_K)

Product of ½ times the mass of man object times the square of an object’s speed.

Change in Gravitational Potential Energy

Product of an object’s mass times the gravitational field strength times the change in height.

Principle of Conservation of Energy

The total energy of an isolated system (no external forces) remains constant. (OR - Energy cannot be created nor destroyed buy only transformed from one form to another or transferred from one object to another.)

Elastic Collision

A collision in which kinetic energy is conserved.

Inelastic Collision

A collision in which kinetic energy is not conserved.

Power (P)

The rate at which work is done or the rate at which energy is transferred.

Newton’s Universal Law of Gravitation

The force of gravity between 2 objects is directly proportional to the product of the two masses and inversely proportional to the square of the distance between them and acts along a line joining their centers.

Gravitational Field Strength (g)

Gravitational force per unit mass on a point mass.

Gravitational Potential Energy (E_P)

The work done in moving a mass from infinity to a point in space (NOTE: The work done is path independent).

Gravitational Potential (V)

The work done per unit mass in moving a mass from infinity to a point in space.

Temperature (T)

1. The property that defines the direction of thermal energy transfer between 2 objects.

2. A measure of the average random kinetic energy of the particles of a substance.

Thermal Equilibrium

2 objects are in thermal equilibrium when they are at the same temperature so that there is no transfer of thermal energy between them.

Internal Energy of a Substance (U)

The total potential energy and random kinetic energy of the molecules of a substance.

Thermal Energy (Heat) (Q)

Energy transferred between 2 substances in thermal conduct due to a temperature difference.

Specific Heat Capacity (c)

Energy required per unit mass to raise the temperature of a substance by 1 K.

Boiling

A phase change of a liquid into a gas that occurs at a fixed temperature.

Evaporation

When faster moving molecules have enough energy to escape from the surface of a liquid that is at a temperature less than its boiling point, leaving slower moving molecules behind which results in a cooling of the liquid.

Specific Latent Heat (L)

Energy per unit mass absorbed or released during a phase change.

Pressure (P)

Force per unit area acting on a surface.

Ideal Gas

A gas that follows the ideal gas equation of state (PV=nRT) for all values of P, V, and T (An ideal gas cannot be liquified).

Real Gas

A gas that does not follow the ideal gas equation of state for all values of P, V, and T (A real gas can approximate an ideal gas in some circumstances).

Absolute Zero of Temperature

Temperature at which a gas would exert no pressure.

Kelvin Scale of Temperature

An absolute scale of temperature in which 0 K is the absolute zero of temperature.

First Law of Thermodynamics (Q=U+W)

The thermal energy transferred to a system from its surroundings is equal to the work done by the system plus the change in internal energy of the system.

Isochoric (Isovolumetric)

A process that occurs at a constant volume (V=0).

Isobaric

A process that occurs at constant pressure (P=0).

Isothermal

A process that occurs at constant temperature (T=0).

Adiabatic

A process that occurs without the exchange of thermal energy (Q=0).

Entropy

A system property that expresses the degree of disorder in the system.

Second Law of Thermodynamics

The overall entropy of the universe is increasing. (OR - All natural processes increase the entropy of the universe.)

Resonance

A transfer of energy in which a system is subject to an oscillating force that matches the maternal frequency of the system resulting in a large amplitude of vibration.

Wave Pulse

Single oscillation or disturbance in a medium.

Transverse Wave

A wave in which the direction of motion of the energy transfer is perpendicular to the direction of motion of the particles of the medium. (NOTE: Light waves are transverse, and transverse waves cannot be propagated in gases.)

Longitudinal Wave

A wave in which the direction of motion of the energy transfer is parallel to the direction of motion of the particles of the medium. (NOTE: Sound waves are longitudinal.)

Wavefront

Collection of neighboring points on a wave that are in phase.

Ray

Line drawn perpendicular to a wavefront indicating the direction of motion of the energy transfer.

Crest

Top of a transverse wave.

Trough

Bottom of a transverse wave.

Compression

Area of high pressure in a longitudinal wave.

Rarefaction

Area of low pressure (expansion) in a longitudinal wave.

Wavelength

Shortest distance along the wave between 2 points in phase with one another.

Wave Speed (v)

Speed of transfer of the energy of the wave.

Intensity (I)

Power received per unit area.

Diffraction

The bending of a wave around an obstacle or the spreading of a wave through an opening. (NOTE: Diffraction is only noticeable when the size of the opening is smaller than or on the same order of the size of the wavelength.)

Principle of Superposition

When 2 waves meet, the resultant displacement is the vector sum of the displacements of the component waves.

Constructive Interference

Superposition of 2 waves which are in phase with each other.

Destructive Interference

Superposition of 2 waves which are out of phase with each other.

Path Difference

Difference in the distances 2 waves must travel from their sources to a given point.

Doppler Effect

The change of frequency of a wave due to the movement of the source or the observer relative to the medium of wave transmission.

Resolution

Ability to distinguish between 2 sources of light.Ray

Rayleigh Criterion

When the central maximum of 1 diffraction pattern overlaps the 1^st minimum of a 2^nd diffraction pattern, the 2 sources are “just resolved.”

Law of Conservation of Charge

The total electric charge of an isolated system remains constant.

Conductor

Material through with electric charge flows freely.

Insulator

Material through which electric charge does not flow freely.

Coulomb’s Law

The electric force between 2 point charges is directly proportional to the product of the 2 charges and inversely proportional to the square of the distance between them, and directed along the line joining the 2 charges.

Electric Field Strength (E)

Electric force per positive unit test charge. (E=F/q)

Radial Field

Field that extends radially. (like the electric field around a point charge or the gravitational field around a planet)

Electric Potential (V)

Work done per unit charge moving a small positive test charge in from infinity to a point in an electric field. (V=W/q) (V=kq/r) (NOTE: The work done is path independent.)

Electric Potential Energy (E_E)

Energy that a charge has due to its position in an electric field.

Ohm’s Law

The current flowing through a device is proportional to the potential difference applied across it, providing the temperature is constant. (NOTE: R=V/I is not a statement of Ohm’s Law.)

Ohmic Device

One whose resistance remains constant over a wide range of potential differences.

Non-Ohmic Devices

One whose resistance does not remain constant over a wide range of potential differences.

Electromotive Force (emf)

Total energy difference per unit charge around a circuit (total energy per unit charge made available by the chemical reaction in the battery).

Internal Resistance (r)

Resistance inside a battery that causes the battery’s terminal potential difference to be less than its emf. (NOTE: Internal resistance in a meter causes it not to act as an ideal meter.)

Magnetic Flux Linkage

Product of the magnetic flux through a single coil and the total number of coils.

Faraday’s Law

The emf induced by a time changing magnetic field is proportional to the rate of change of the flux linkage.

Lenz’s Law

The direction of an induced emf is such that it produces a magnetic field whose direction opposes the change in magnetic field that produced it. (NOTE: This is the negative sign added to Faraday’s Law.)

Nuclide

A particular type of nucleus with a certain number of protons or neutrons.

Isotope

Nuclei with the same number of protons but different number of neutrons.

Nucleon Number (Mass Number) (A)

Number of nucleons (protons + neutrons) in the nucleus.

Proton Number (Atomic Number) (Zero)

Number of photons in the nucleus.

Neutron Number (N)

Number of neutrons in the nucleus. (N=A-Z)

Mass Defect

Difference between the mass of the nucleus and the sum of the masses of its individual nucleons.

Binding Energy

Energy released when a nuclide is assembled from its individual components. (OR: Energy required when the nucleus is separated into its individual components.)

Binding Energy per Nucleon

Energy released per nucleon when a nuclide is assembled from its individual components. (OR: Energy required per nucleon when nucleus is separated into its individual components.)

Nuclear Fission

A heavy nucleus splits into 2 smaller nuclei of roughly equal mass.

Nuclear Fusion

2 light nuclei join to form a heavier nucleus. (NOTE: This is the main source of the Sun’s energy.)

Photoelectric Effect

The emission of electrons from a metal when electromagnetic radiation of high enough frequency falls on the surface.

Threshold Frequency (f₀)

Minimum frequency of light needed to eject electrons from a metal surface.

Work Function

Minimum energy needed to eject electrons from the surface of a metal.

Albedo

Fraction of the total incoming solar radiation received by a planet that is reflected back out into space. (OR: Ratio of total solar radiation power scattered by a planet to total solar radiation received by a planet.) (NOTE: Global annual mean albedo is 0.3 for earth.)

Greenhouse Effect

Short wavelength radiation received from the Sun causes the Earth’s surface to heat up. Earth will then emit longer wavelength radiation (infrared) which is absorbed by some gases (methane, water vapor, carbon dioxide, nitrous oxide) in the atmosphere and re-radiated in all directions.

Global Warming

Increase of mean temperature of the Earth in recent years.