IB Physics Definitions

Topic 1 to 6, Option B: Engineering

Accurate

average value moves towards the true value

Precise

data are closer together / sharper peak

Random error

readings have positive and negative values around the average value / values are scattered / wide range

Systematic error

• error that is identical for each reading or error caused by zero error in instrument

• For graphs: when every data point deviates from the “correct” value by the same fixed amount as seen by intercept on the graph

• the average is not the true value / the readings are not centred around the true value

Zero error

• a non-zero reading when a zero reading is expected

• a calibration error

Acceleration

• change in velocity / rate of change of velocity

• per unit time / with respect time

Average speed

**Alt 1:** speed over a period of time/distance

**Alt 2:** The ratio of distance travelled over the change in time

Conservation of energy

energy can not be created or destroyed, it only changes form

Conservation of momentum

**Alt 1:** if the net external force acting on a system is zero, the momentum of the system remains constant/unchanged/the same

**Alt 2:** for a closed system, the momentum remains constant/unchanged/the same

Coefficient of friction

ratio between (maximum) friction and normal reaction

{Don’t accept equation without definitions of symbols}

Elastic collision

a collision in which __kinetic__ energy is not lost / __kinetic__ energy is conserved

Force

net force is rate of change of momentum

Impulse

**Alt 1:** change in momentum

**Alt 2:** force × time (time for which the force acts)

Instantaneous speed

**Alt 1:** the speed at a particular instant in time/point in space

**Alt 2:** the magnitude of instantaneous velocity in time/point in space

Linear Momentum

product of mass and __velocity__

Newton’s first law

a body continues at rest or constant velocity unless acted on by a resultant (external) force

Newton’s second law

the rate of change of momentum of a body is equal to/directly proportional to the force acting on the body

Newton’s third law of motion

**Alt 1:** when two bodies A and B interact the force that A exerts on B is equal and opposite to the force that B exerts on A

**Alt 2:** if object A exerts a force on object B, then object B (simultaneously) exerts an equal and opposite force on object A

**Alt 3:** every action has an equal and opposite reaction

Power

**Alt 1:** the rate at which work is being performed

**Alt 2:** work done divided by time taken

Work

**Alt 1:**

• work done = force × distance moved

• (distance moved) in direction of force

**Alt 2:**

• energy transferred

• from one location to another

**Alt 3:**

• work done = Fs cos (θ)

• with each symbol defined

Centre of gravity

• point where weight/gravitational force of object

• may be considered / appears to act

Moment of a force

product of the force and the perpendicular distance (to the pivot)

Moment of inertia

**Alt 1:** an object’s ability to resist a change in rotational motion

**Alt 2:** equivalent of mass in rotational equations

Rotational equilibrium

sum of the (net) torques/moments of the forces is zero

Stress

equal to force per unit area

Strain

• extension from original length

• proportional to ratio of length of strain over original length

Torque

• ability of a force to produce rotation

• equal to the product of magnitude of a force and distance from axis of rotation

• with reference to the angle between the force and distance from axis of rotation

Couple

pair of equal parallel forces that are opposite in direction

Equilibrium

• sum of forces acting on the object is zero

• sum of torques on the object is zero

Boyle’s law

for an __ideal gas__ at constant temperature, pressure is inversely proportional to volume

Heating of copper

• the non-mechanical transfer of energy

• from the surroundings/source to the copper

Ideal Gas

**Alt 1:** a gas that obeys the universal gas law / ideal gas law at __all pressures, volumes and temperatures__

**Alt 2:** a gas in which there are no intermolecular forces;

**Alt 3:** molecules have zero PE / only KE

Ideal gas assumptions

• large number of identical particles

• particles move in random motion at high speeds

• no intermolecular forces

• all collisions are elastic

• duration of collisions much less than time between collisions

• volume of molecules is negligible to volume of container

Internal energy

sum of random kinetic energy and intermolecular potential energy in particles

Mole

**Alt 1:** the molecular weight of the element in grams

**Alt 2:** 6.02 x 10^23 element atoms

**Alt 3:** equal to the number of particles in 12 g of Carbon-12

Specific heat capacity

the thermal energy required to change the temperature of a substance by a unit degree (1°C or 1 K) per unit mass

Specific latent heat of fusion

**Alt 1:** thermal energy absorbed when a unit mass of liquid freezes __at a constant temperature__

**Alt 2:** thermal energy released when a unit mass of solid melts __at a constant temperature__

Specific latent heat of vaporization

quantity of thermal energy required to convert a unit mass of liquid to gas __at a constant temperature__

Temperature

**Alt 1:** proportional to a measure of the average kinetic energy of the particles of a substance

**Alt 2:** macroscopic measure of average kinetic energy of particles of a substance

Heat/Thermal capacity

• thermal energy required to increase the temperature of a substance by a unit degree (1°C or 1 K)

• equal to mass × specific heat capacity

Thermal energy

the non-mechanical transfer of energy between two different bodies as a result of a temperature difference between them

Thermal equilibrium

rate of __energy__ absorption is equal to the rate of __energy__ emission

Open system

a system in which mass cannot enter and leave

Closed system

a system in which mass cannot enter and leave

Isolated system

a system in which energy cannot enter or leave

Monatomic gas

a gas that consists of particles that have single atoms

Adiabatic process

• a change in the pressure, volume and temperature of the system • in which no thermal energy transferred between the system and the surroundings

Isobaric process

a process that takes place at constant pressure

Isochoric (isovolumetric) process

a process that takes place at constant volume

Isothermal process

a process in which temperature remains constant

Isothermal-Isobaric process

a process that takes place at constant temperature and pressure

First law of thermodynamics

• the energy transferred between a system and its surroundings

• is equal to the work done on the system plus the change in internal energy of the system

Second law of thermodynamics

**Alt 1:** the total entropy of an isolated system never decreases

**Alt 2:** the total entropy of the universe is always increasing

**Alt 3 (Clausius):** work is required to be supplied in order for thermal energy to flow from a cold to a hot object

**Alt 4 (Kelvin):** In a __cyclic process__, it is impossible to completely convert heat into mechanical energy

Cyclic process

a process in which the initial and final state are the same

Entropy

the measure of disorder in a system

Heat engine

a device that converts thermal energy into mechanical work

Carnot engine

• consists of two isothermal and two adiabatic thermodynamic processes

• no engine can be more efficient than a Carnot engine operating between the same temperatures

Oscillation

the cyclical (repeating) motion of an object

Simple harmonic motion

• Force/acceleration is proportional to the displacement/distance from the equilibrium point/mean position;

• directed towards the equilibrium point / in opposite direction to displacement/distance;

Amplitude

the maximum displacement of the system from equilibrium/centre of motion

Displacement (waves)

distance in a particular direction of a particle from its mean position

Coherent

__constant/zero phase difference__ between light waves

Coherence sources

sources whose phase difference is constant

Electromagnetic wave \[2\]

• oscillating/vibrating electric and magnetic fields;

• at right angles to each other;

• at right angles to the direction of propagation/energy transfer of the wave/ velocity/transverse;

• which can travel through a vacuum;

Frequency (waves)

number of vibrations/oscillations __per unit time__

Wavelength

distance moved by wave during one oscillation of the source

Wave speed (speed of wave)

• distance travelled per unit time

• by the energy in a wave / by a wavefront

Wave speed (energy)

rate at which energy is propagated along the wave

Intensity (waves)

equal to power per unit area

Constructive interference

• when two waves meet

• resultant displacement is found by summing the individual displacements

• to give maximum displacement

Principle of Superposition (Inte)

when two waves overlap/interfere/meet, the resultant __displacement__ of the particles is the sum of their individual __displacements__

Monochromatic

light with the same wavelength/frequency

Antinode

the position of maximum amplitude in a standing wave

Node

point in a standing wave with zero amplitude

Polarized light

**Alt 1:** light in which the __electric__ field vibrates only in one plane

**Alt 2:** __electric field__ vector oscillates in a fixed plane

Unpolarized light

all possible polarization directions are equally represented

Ray

• direction which energy of wave travels

• at right angles/perpendicular to the wavefront

Wavefront

• line that joins points in a wave with the same phase

• at right angles/perpendicular to wave rays

Resonance

• maximum amplitude of oscillation

• when a periodic force is applied to it

• frequency of the force is equal to the natural frequency of vibration of the system

Longitudinal wave

a wave where the displacement of __oscillations__ of particles is parallel to the direction of __energy__ propagation/transfer

Transverse wave

a wave where the direction of __energy__ propagation/transfer is at right angles to the __vibration__ of the particles in the medium

Continuous travelling wave

• energy transfer

• with no interruption in transfer / without mass motion of the medium

Travelling (progressive) wave

a wave that transfers energy between points in a medium

Standing wave

a wave that forms when two travelling waves of equal amplitude and frequency are traveling in opposite directions

Refractive index

the ratio of the speed of light in a vacuum to the speed of light in a substance

Critical angle

**Alt 1:**

• when the (transmitted) ray/light in medium 2 is along the boundary/refracted at 90° ;

• the angle of incidence in medium 1 is the critical angle;

**Alt 2:**

• when a ray/light is incident on the boundary at an angle greater than the critical angle;

• the ray is not transmitted / no light is transmitted but is totally reflected at the boundary / is totally internally reflected;

Total internal reflection

for a ray attempting to move from a high to a low refractive index medium, the phenomena in which the angle of incidence is greater than the critical angle, which is the angle of incidence for which the angle of refraction is 90°, leading to a reflected but not to a refracted ray;

Diffraction

spreading out/bending of a wave when it meets an aperture/gap/slit/obstacle;

Charge

the scalar quantity of matter that can cause it to experience a force in the electromagnetic field

Coulomb’s law

• the magnitude of electrostatic force between two point charges

• is directly proportional to the product of their magnitudes of charges and inversely proportional to the square of their separation

Electrical permittivity

the measure of the resistance offered by a substance in creating an electric field

Electric current

**Alt 1:** The amount of charge that flows through a cross-sectional area of a conductor per unit time.

**Alt 2:** Rate of flow of chart through a conductor;

Electric field

area of space where a charge experiences a force

(a vector field that associates each point in space the Coulomb force that would be experienced per unit charge by a point charge at that location)

Electric field strength

magnitude of electric force per unit charge acting on a positive test charge at a point in an electrical field

Electric potential difference

work done/energy per unit charge to move positive test charge between points in an electric field

Electric resistance

potential difference across the wire divided by the current through the wire

Electromotive force

**Alt 1:** the work done per unit charge in moving a quantity of charge __completely__ around a circuit

**Alt 2:** the power delivered __by the supply__ per unit current

Internal resistance of a cell

• resistance of the components/chemicals/materials within the cell itself

• leading to energy/power loss/dissipated in driving current through the cell;

Ideal voltmeter

a voltmeter with an infinite resistance

Ideal ammeter

an ammeter whose resistance is zero