PHYSiCS BALLS

Work (W)

When a force is applied through a displacement; SI unit = Joule (J) = 1 N·m

Joule (J)

The SI unit of work, equal to 1 N·m

Watt

A unit of power equal to 1 J/s

Work-energy theorem

The work done on a system results in a change in kinetic energy (W = ΔKE = ½mv²)

Power

P = W/t

Translational kinetic energy

Energy due to changing position (KE = ½mv²)

Rotational kinetic energy

Energy due to rotational motion (KE_rot = ½Iω²)

Potential energy

Energy stored due to interactions between objects in a system

Gravitational potential energy (GPE)

Stored energy due to gravity (GPE = mgh)

Reference level

The position where GPE is defined to be zero (ground)

Elastic potential energy

Stored energy due to an object's deformation

Internal energy

The sum of kinetic and potential energy of the particles in a system; associated with temperature

Law of conservation of energy

In a closed, isolated system, total energy can neither be created nor destroyed

Mechanical energy (ME)

The sum of KE and PE of the objects in a system (ME = KE + PE)

Elastic collision

A collision in which kinetic energy does not change

Inelastic collision

A collision in which kinetic energy is lost

Simple machine

A device that does tasks by changing the magnitude or direction of the applied force

Efficiency

The ratio of output work to input work (W_out / W_in × 100%), or AMA/IMA × 100%

Resistance force

The force a machine needs to overcome

Mechanical advantage (MA)

The ratio of resistance force to effort force; how much a machine multiplies force

Actual mechanical advantage (AMA)

AMA = F_resistance / F_effort

Ideal mechanical advantage (IMA)

IMA = d_effort / d_resistance

Compound machine

Two or more simple machines combined so the resistance force of one acts as the effort force of the next

Periodic motion

When an object's position repeats at regular time intervals

Amplitude

The maximum distance an object moves from equilibrium

Period

The time for one full oscillation

Equilibrium position

The position where the net force on the object is zero

Spring constant

The magnitude of force per unit displacement (F = kx)

Simple pendulum

A mass on a string that oscillates at a natural frequency

Resonance

When forces are applied to a vibrating object at its natural frequency, causing the amplitude to increase

Wave

A disturbance that carries energy through space without transferring matter

Wave pulse

A single bump or disturbance that moves through a medium

Transverse wave

A wave in which particles are displaced perpendicular to the direction of travel

Periodic wave

A continuous wave where the disturbance repeats at a constant rate

Longitudinal wave

A wave in which the displacement of the medium is parallel to the direction of travel

Surface wave

A wave where medium particles follow a circular path — at times parallel, at other times perpendicular to the direction of travel

Trough

The lowest point on a transverse wave

Crest

The highest point on a transverse wave

Thermal conduction

The transfer of thermal energy that occurs when particles collide

Thermal equilibrium

When thermal energy transfer between two objects ceases because they are at the same temperature

Heat (Q)

The transfer of thermal energy from a hotter object to a cooler one

Conduction

Heat transfer mainly caused by the motion of fluid or a temperature difference

Radiation

The transfer of energy by electromagnetic waves

Specific heat

The energy needed to raise 1 kg of a substance by 1 K (unit: J/(kg·K))

Heat of fusion

The energy needed to melt 1 kg of a substance

Heat of vaporization

The thermal energy needed to vaporize 1 kg of a liquid

First law of thermodynamics

The change in internal energy (ΔU) equals heat added (Q) minus work done by the object: ΔU = Q − W

Heat pump

A device that continuously converts mechanical energy into thermal energy transfer

Entropy

The result of the dispersal of energy; systems tend toward uniform energy distribution and more probable states

Sound wave

A pressure oscillation that is transmitted through matter

Pitch

The highness or lowness of a sound

Loudness

The intensity of a sound as sensed by the human ear and brain

Sound level

A logarithmic scale that shows how humans hear loudness

Decibel

The common unit for sound level

Closed-pipe resonator

A resonating tube with one end closed

Open-pipe resonator

A resonating tube with both ends open that will resonate to a sound source

Fundamental

The lowest frequency of sound that resonates in a tube

Harmonics

Higher frequencies; multiples of the fundamental frequency

Dissonance

A set of pitches that our ears perceive as unpleasant/clashing

Doppler effect

The change in frequency of sound caused by movement of the source, the observer, or both, relative to each other

Ray model of light

The idea that light travels in straight-line paths and can be reflected/refracted when encountering a boundary

Luminous object

An object that produces its own light

Opaque object

An object that reflects and absorbs light but doesn't transmit it

Translucent

A material that transmits and reflects light but does not allow objects to be seen clearly through it

Transparent

A material (e.g. glass, air) that most light passes through

Illuminance

The luminous flux falling on a given surface (unit: lux)

Diffraction

The bending of waves around an obstacle or through an opening

Primary colors (light)

Red, blue, and green — the three colors from which all others can be made

Secondary color (light)

A mix of two primary colors

Complementary colors

Two colors that combine to produce white light

Primary pigment

A pigment that absorbs only one of the primary colors

Secondary pigment

A pigment that absorbs two of the primary colors and reflects one

Polarization

The production of light with a specific pattern of oscillation

Emission spectrum

A graph of the intensity of the radiation emitted from an object at different frequencies

Quantized

When energy only exists in specific discrete amounts

Photoelectric effect

The release of electrons when electromagnetic photons strike a surface

Photovoltaic effect

When photons hit a solar cell, causing it to emit a current

Photon

A discrete quantum bundle of light energy

Work function

The energy needed to free the outermost bound electron from the atom

de Broglie wavelength

Equal to Planck's constant divided by the particle's momentum (λ = h/mv)

Heisenberg Uncertainty Principle

There is a limit to how precisely a particle's position and momentum can simultaneously be known

Alpha particles

Positively charged particles emitted at high speed from a nucleus

Nucleus

Where all of an atom's positive charge resides in the tiny core

Absorption spectrum

The set of frequencies absorbed by a gas

Energy levels

The discrete amounts of energy an electron can have

Ground state

The lowest attainable energy state

Excited state

A higher energy state

Bohr model / probability cloud

The region in which there is a high probability of finding the electron

Wave-particle duality

The property of matter/light behaving as both a wave and a particle

Nucleon

Protons and neutrons

Atomic number (Z)

The number of protons in an atom

Mass number (A)

The number of nucleons in an atom

Atomic mass unit (amu)

A unit of mass equal to 1.66×10⁻²⁷ kg; approximately the mass of one nucleon

Strong nuclear force

An attractive force between nucleons that are close together

Mass defect

The difference between the sum of the masses of individual nucleons and the actual nucleus mass

Binding energy

The energy equivalent of the mass defect; energy required to break apart a nucleus

Alpha decay

Emission of an alpha particle (helium nucleus) from the nucleus

Beta decay

When a neutron changes to a proton, emitting an electron or positron

Gamma ray

When there is a redistribution of energy within the nucleus, a gamma ray is emitted

Half-life

The time required for half the atoms in a given amount of a radioactive isotope to decay