WACE ATAR Physics cheat sheet

Independent variable is deliberately changed by the experimenter; dependent variable is measured; all others are controlled.

Repeat trials reduce random error; a systematic error shifts all readings the same way and is not reduced by averaging.

Precision describes agreement between repeated measurements; accuracy describes closeness to the accepted value.

Percentage error = |measured − accepted| / accepted × 100%; percentage uncertainty for a scale is half the smallest division divided by the reading.

Uncertainties add in quadrature for independent quantities: if z = x/y then Δz/z = √((Δx/x)² + (Δy/y)²).

A valid conclusion follows only if variables were controlled and the sample or trial count is adequate; correlation in observational data does not establish causation.

Gradient of a linearised graph gives the physical constant; units of gradient equal units of y divided by units of x.

Reliability improves with more trials and consistent method; validity requires the procedure to actually test the stated hypothesis.

Peer review requires independent expert scrutiny before publication; it filters weak methods but does not guarantee correctness.

A scientific model is accepted when it predicts new observations, not merely when it explains existing ones; Newtonian mechanics fails at speeds near c and at atomic scales.

Technology and science are reciprocal: the telescope enabled Galileo's observations, and quantum theory enabled semiconductors.

Collaboration across nations is standard in physics, e.g. the LHC involves over 100 countries; data and authorship conventions are negotiated socially.

Funding and policy shape which research proceeds; public controversies (e.g. nuclear power, wi-fi) often concern risk perception rather than disputed physics.

A hypothesis is falsifiable if some conceivable observation would contradict it; unfalsifiable claims lie outside empirical science.

Consensus emerges from converging independent lines of evidence, not from a single decisive experiment.

Measurement standards (the SI second, metre, kilogram) are social conventions maintained by international agreement, now defined via fixed constants.

Newton's second law: net force equals mass times acceleration (F = ma); weight W = mg with g ≈ 9.8 m/s² near Earth's surface.

Momentum p = mv is conserved in collisions when net external impulse is zero; kinetic energy is conserved only in elastic collisions.

Work W = Fd cos θ; work–energy theorem: net work equals change in kinetic energy.

Uniform circular motion requires centripetal force F = mv²/r directed toward the centre; speed constant, velocity changing.

Hooke's law F = kx holds within the elastic limit; elastic potential energy stored = ½kx².

Conservation of energy: energy transfers between kinetic, gravitational potential (mgh), elastic, thermal and other forms; total in a closed system is constant.

Wave equation v = fλ; for a wave crossing a boundary frequency is unchanged while speed and wavelength change.

Electric field strength E = F/q; potential difference V = W/q; for uniform fields between parallel plates E = V/d.

Equations of uniform acceleration: v = u + at; s = ut + ½at²; v² = u² + 2as.

Projectile motion: horizontal velocity constant (no air resistance); vertical acceleration g downward; time of flight set by vertical motion.

Refraction obeys Snell's law n₁ sin θ₁ = n₂ sin θ₂; total internal reflection occurs above the critical angle sin θc = n₂/n₁.

Standing waves on a string fixed at both ends: λ = 2L/n; fundamental f₁ = v/(2L).

Coulomb's law F = kq₁q₂/r²; gravitational force F = GMm/r²; both are inverse-square and act along the line joining centres.

Ohm's law V = IR for ohmic conductors at constant temperature; resistors in series add, in parallel 1/R = Σ1/Rᵢ.

Magnetic force on a current-carrying wire F = BIL sin θ; on a moving charge F = qvB sin θ, direction given by the right-hand rule.

Photoelectric effect: maximum kinetic energy of emitted electrons = hf − φ, where φ is the work function; below threshold frequency no emission occurs.

Significant figures: the result of multiplication or division carries the same count as the least precise input.

Random error is estimated by the spread of repeats (e.g. half the range); report results as value ± uncertainty with matching decimal places.

A control group isolates the effect of the independent variable by receiving no treatment or a placebo.

Linearising a relationship (e.g. plotting T² against L for a pendulum) allows a straight-line gradient to yield the constant of interest.

Graph axes must be labelled with quantity and unit; a line of best fit balances points above and below rather than joining them.

An anomalous point is excluded only with a stated physical reason, not simply because it is inconvenient.

Risk assessment identifies hazard, likelihood and severity, then specifies a control; in physics practicals this includes electrical and laser safety.

A hypothesis must be testable and specific, stating the expected relationship between the independent and dependent variables.

Einstein's 1905 papers on special relativity and the photoelectric effect initially met resistance; acceptance came from prediction and experiment, not authority.

The shift from Newtonian to relativistic mechanics shows that theories are provisional and replaced when new evidence demands it.

Large-scale physics relies on peer-reviewed collaboration papers with thousands of authors; credit conventions differ from small-team science.

The development of the atomic bomb illustrates that scientific knowledge can be applied for purposes beyond the researchers' control, raising ethical questions.

International adoption of SI units and the caesium atomic clock standard shows metrology as an agreed human framework underpinning trade and navigation.

Public debate over renewable energy frequently involves evaluating evidence quality and risk, not only the underlying physics.

Models such as the standard model of particle physics are judged by predictive power and are revised when anomalies persist.

Historical bias can delay recognition; e.g. contributions of many researchers to the discovery of nuclear fission spanned several countries and were shaped by wartime secrecy.

Impulse J = FΔt equals change in momentum; a longer contact time reduces the average force for a given momentum change.

Newton's third law: forces occur in equal and opposite pairs acting on different bodies, so they never cancel on a single object.

Torque τ = Fd sin θ about a pivot; a body in rotational equilibrium has zero net torque and zero net force.

Pressure in a fluid increases with depth: P = P₀ + ρgh; Archimedes' principle gives buoyant force equal to weight of displaced fluid.

Thermal energy transfer Q = mcΔT; latent heat Q = mL applies at constant temperature during a phase change.

Work done by a gas at constant pressure W = PΔV; the first law of thermodynamics is ΔU = Q − W (work done by the gas).

Acceleration due to gravity is independent of mass in the absence of air resistance; terminal velocity occurs when drag equals weight.

Average velocity equals displacement divided by time; average speed equals distance divided by time; the two differ when direction changes.

Doppler effect for sound: observed frequency f' = f(v ± v_observer)/(v ∓ v_source), with signs chosen so approach raises frequency.

Diffraction is greatest when wavelength is comparable to slit width; double-slit maxima occur at d sin θ = mλ.

Intensity of a wave from a point source obeys the inverse-square law I ∝ 1/r² in three dimensions.

Electric potential energy between point charges U = kq₁q₂/r; potential V = kq/r with zero at infinity.

Capacitors in series: 1/C = Σ1/Cᵢ; energy stored U = ½CV² = ½QV.

Magnetic flux Φ = BA cos θ; induced emf equals the negative rate of change of flux (Faraday's law), with Lenz's law giving the direction.

An ideal transformer satisfies V_s/V_p = N_s/N_p and, for full power transfer, I_p V_p = I_s V_s.

Photon energy E = hf = hc/λ; the electron volt is the energy gained by one electron accelerated through 1 V (1 eV ≈ 1.6 × 10⁻¹⁹ J).