Launch it.
Fire a projectile with and without drag, split light through two slits, and watch a nucleus decay — three AQA A-Level Physics models you drive yourself.
Projectile motion, with the air switched on
FIG. 01 · MECHANICS · 3.4.1.3Resolve it once: ux = u cos θ stays constant, uy = u sin θ is the only bit gravity touches.
Complementary angles (30° and 60°) give identical range in a vacuum. Try it.
Modelled as a drag force proportional to v², opposing motion (k = 0.006 m⁻¹, a light ball). g = 9.81 m s⁻².
In the exam: the standard question gives you u and θ and expects the suvat treatment — vertical and horizontal motion handled separately, with time as the shared quantity. Range peaks at exactly 45° only when air resistance is ignored; switch drag on and the optimum angle drops, the path becomes asymmetric (steeper on the way down), and both range and time of flight fall. Saying "the trajectory is a parabola" is only worth a mark if you have already said "assuming air resistance is negligible".
Two slits, one screen, countable fringes
FIG. 02 · INTERFERENCE · 3.3.2.1Monochromatic and coherent — a laser, or one slit illuminating both.
Closer slits push the fringes further apart — w and s are inversely proportional.
Measure across ten fringes and divide — that is the required-practical trick for cutting uncertainty.
Path difference at the probe is (s × y) / D.
In the exam: w = λD/s is on the data sheet, and you will be asked to rearrange it to find λ from measured fringes. The marks live in the reasoning: bright fringes where the path difference is a whole number of wavelengths (nλ, constructive, waves in phase); dark where it is an odd number of half-wavelengths ((n + ½)λ, destructive). The pattern only exists because the sources are coherent — constant phase difference and the same frequency.
Decay is exponential, and it never quite finishes
FIG. 03 · RADIOACTIVITY · 3.8.1.3Faint verticals mark successive half-lives: each one halves whatever is left, wherever you start.
Sample starts with N₀ = 1.00 × 10¹² undecayed nuclei.
On the log axis the curve straightens: gradient = −λ. That is how a half-life is measured in practice.
In the exam: the two equations that do all the work are N = N₀e−λt and λT½ = ln 2, with activity A = λN. Watch the units — λ from a half-life in days must be converted to s⁻¹ before an activity in becquerel means anything. Decay is random and spontaneous: you cannot say which nucleus goes next, only that each has the same constant probability per unit time, which is exactly why the curve is exponential and never reaches zero.