Women in Physics Pixel Sticker Sheet

9 pixel-art physics stickers on one A5 (5.83″ × 8.27″) white kiss-cut sheet: Women in Physics. Every character below has its own sticker page with the full physics panel.

Lise Meitner

When a uranium nucleus splits, the pieces weigh less than the original, and the missing mass appears as energy. Meitner and Frisch estimated it from the electric repulsion between the two fragments at the moment they part: about 200 MeV per fission.

Q = (M_initial − M_final)c²

Q: energy released (quoted in MeV) (J); M: total rest mass before/after (kg); c: speed of light (m/s); E_C: Coulomb repulsion energy of two touching fragments (J); Z₁, Z₂: fragment proton numbers; e: elementary charge (C)

Marie Curie

Each radioactive nucleus has a fixed chance per second of decaying, so the number left falls exponentially. The half-life is ln 2 divided by that decay constant, and the activity is the decay constant times the number of nuclei.

N(t) = N₀ e^(−λt)

N: number of undecayed nuclei; λ: decay constant (s⁻¹); t_(1/2): half-life (s); A: activity (1 Bq = 1 decay per second) (Bq)

Chien-Shiung Wu

In Wu's experiment, cobalt-60 nuclei were lined up by a magnetic field, and the electrons from their beta decay came out preferentially opposite to the nuclear spin. A mirror image of that experiment would show the reverse, so the weak force distinguishes left from right.

⁶⁰Co → ⁶⁰Ni* + e⁻ + ν̄_e

J: nuclear spin (axial vector) (J·s); pₑ: electron momentum (polar vector) (kg·m/s); ̂P: parity (mirror) operation

Jocelyn Bell Burnell

A pulsar's very regular pulses mean it must be extremely dense to spin that fast without flying apart, which points to a neutron star. Radio pulses at lower frequencies arrive later after passing through interstellar electrons, and that delay measures how many electrons lie along the way.

ρ̄ ≳ 3π/(GP²)

ρ̄: minimum mean density for a body spinning with period P not to fly apart (kg/m³); G: gravitational constant (m³·kg⁻¹·s⁻²); P: rotation period (s); Δ t: arrival-time delay between frequencies f₁ < f₂ (s); DM: dispersion measure, ∫ nₑ dl (free electrons per area along the line of sight) (m⁻²); f₁, f₂: observing frequencies (Hz)

Vera Rubin

If most of a galaxy's mass were in its bright centre, stars far out would orbit more slowly. Vera Rubin found the speeds stay roughly constant far out, which means the enclosed mass keeps growing with radius: unseen matter.

v(r)² = GM(r)/r

v(r): circular orbital speed (m/s); M(r): enclosed mass (kg); r: radius (m); G: gravitational constant (m³·kg⁻¹·s⁻²)

Emmy Noether

Noether's theorem says that every continuous symmetry of a system's laws comes with a conserved quantity. Symmetry under shifts in time gives conservation of energy, shifts in space give momentum, and rotations give angular momentum.

Q = Σ_i (∂L/∂q̇_i) δq_i

Q: conserved Noether charge (momentum for a shift, angular momentum for a rotation) (kg·m/s, J·s); L: Lagrangian (J); qᵢ: generalised coordinates (lengths or angles) (m, rad); ̇qᵢ: generalised velocities (m/s, rad/s); ε: small symmetry parameter (a length for a shift, an angle for a rotation, a time for a clock shift) (m, rad, s); δ qᵢ: direction of the symmetry shift (its size is carried by ε)

Cecilia Payne-Gaposchkin

Saha's equation gives how much of each element is ionized in a hot gas at a given temperature and density. Cecilia Payne used it to correct for ionization in stellar spectra, and showed that stars are made mostly of hydrogen and helium.

n_i+1n_e/n_i = (2/Λ³)(g_i+1/g_i) exp(−χ_i/(k_BT))

nᵢ, nᵢ₊₁: number densities of ionisation stages i and i+1 (m⁻³); nₑ: electron number density (m⁻³); gᵢ: statistical weight of stage i; χᵢ: ionisation energy from stage i (J); k_B: Boltzmann constant (J/K); T: temperature (K)

Émilie du Châtelet

Kinetic energy grows with the square of speed, so twice the speed carries four times the energy. Du Châtelet used experiments with balls dropped into clay, where the dent depth grew with the square of the speed, to argue for this 'vis viva' measure.

E_k = ½mv²

E_k: kinetic energy (J); m: mass (kg); v: impact speed (m/s); g: gravitational acceleration (m/s²); h: drop height (m); F: average resisting force of the clay (assumed constant) (N)

Maria Goeppert Mayer

Protons and neutrons fill energy shells in the nucleus, much like electrons in an atom. Adding strong spin-orbit coupling moves the shell gaps to the observed magic numbers 2, 8, 20, 28, 50, 82 and 126, where nuclei are unusually stable.

E_N = ħω(N + 3/2)

E_N: energy of oscillator shell N (J); N: oscillator shell number; ħω: oscillator level spacing (J); g_N: states in shell N per nucleon species (spin included); V_(ℓ s): spin–orbit potential (J); C(r): radial strength of the spin–orbit term (with orbital and spin angular momentum measured in units of ħ) (J)