This mini-lesson covers the whole of CCEA Unit AS 1: physical quantities and units, scalars & vectors, the principle of moments, linear motion and projectiles, Newton's laws, momentum & impulse, work, energy & power, and electricity — current, p.d., e.m.f., resistance, resistivity, internal resistance and potential dividers.
Work through each screen, answer the questions (several are full A-level calculations) and collect ⭐ stars. Press Start when you are ready.
Every physical quantity is a numerical magnitude together with a unit. All units can be built from six SI base units:
Derived units are combinations. For example the newton: since F = ma, 1 N = 1 kg m s−2. The joule: W = Fs, so 1 J = 1 kg m2 s−2.
Prefixes you must recall: T (1012), G (109), M (106), k (103), c (10−2), m (10−3), µ (10−6), n (10−9), p (10−12), f (10−15). Convert to standard form before substituting: 4.7 kΩ = 4.7 × 103 Ω; 220 µF = 2.20 × 10−4 F.
A scalar has magnitude only (mass, speed, energy, time). A vector has magnitude and direction (displacement, velocity, acceleration, force, momentum).
A vector F at angle θ to the horizontal splits into two perpendicular components:
Equilibrium: for two or three coplanar forces acting at a point, equilibrium means the vector sum is zero — the force arrows form a closed triangle. Resolve in two perpendicular directions and set each total to zero.
The moment of a force about a point is the force multiplied by the perpendicular distance from the point to the line of action of the force.
The centre of gravity is the single point where the whole weight of the body appears to act. For a uniform beam it is at the geometric centre — so the beam's weight acts there in your moments equation.
Two conditions for equilibrium: (1) the resultant force is zero (so it does not accelerate); (2) the resultant moment about any point is zero (so it does not rotate). You need both.
For uniform acceleration in a straight line (u = initial velocity, v = final velocity, a = acceleration, s = displacement, t = time):
On a velocity–time graph the gradient is the acceleration and the area under the graph is the displacement. On a displacement–time graph the gradient is the velocity.
Projectiles. Motion under gravity (ignoring air resistance) is a uniform velocity horizontally combined with a uniform acceleration (g downwards) vertically. The two are independent — the only quantity they share is the time.
Horizontal: a = 0, so x = uxt.
Vertical: a = g = 9.81 m s−2 down, so use the suvat equations with uy.
Find t from the vertical motion, then feed that t into the horizontal equation.
Free-fall experiment (1.4.3): drop a ball through two light gates connected to a computer; software records the time between gates and the gate separation, giving g from the velocities. Repeat and average to reduce random error.
Classic trap: the weight of a book on a table and the normal contact force on the book are not a Newton's third law pair — they act on the same body and are different types of force. The third-law partner of the book's weight is the gravitational pull of the book on the Earth.
Momentum p = mv (kg m s−1) — a vector, so direction and sign matter.
Conservation of linear momentum: in the absence of external forces, the total momentum before a collision equals the total momentum after. This is true for all collisions.
Confirm it by calculation: work out total ½mv² before and after. If they are equal, the collision was elastic; if the total KE has fallen, it was inelastic. Momentum should balance either way — if it does not, you have a sign error.
Tap an item, then tap the box it belongs in.
Work done = force × distance moved in the direction of the force. If the force is at an angle θ to the motion, only the component along the motion does work:
Power is the rate of energy transfer:
Conservation of energy in practice: for an object falling freely, the loss of gravitational p.e. equals the gain in k.e.: mgΔh = ½mv², so v = √(2gΔh) — the mass cancels. Where friction or drag act, some energy is dissipated as internal energy, so efficiency is below 100%.
Current is the rate of flow of charge:
Potential difference (p.d.) is the energy transferred from the charge per unit charge as it passes through a component:
E.m.f. (E) is the energy given to each coulomb of charge by the source. It is also measured in volts.
The distinction CCEA wants: e.m.f. = energy converted from another form into electrical energy per coulomb (in the source). P.d. = electrical energy converted out of the circuit per coulomb (in a component). Same unit, opposite direction of energy conversion.
Resistivity ρ (unit: Ω m) is a property of the material, not the sample: a wire's resistance rises with length and falls with cross-sectional area. To measure it, plot R against L for a wire of known diameter — gradient = ρ / A, with A = πd²/4 from a micrometer reading.
Ohm's law: the current through a metallic conductor is directly proportional to the p.d. across it, provided the temperature is constant.
Thermistor (ntc): as temperature rises, more charge carriers are released, so its resistance falls. A metal does the opposite — hotter ions vibrate more, scattering electrons, so resistance rises. A superconductor below its critical temperature has zero resistivity.
A real cell has internal resistance r. Some of the e.m.f. is 'lost' driving current through the cell itself (the lost volts, Ir), so the terminal p.d. you actually measure is:
A potential divider uses two resistors in series to tap off a fraction of the supply. Because the same current flows through both, the p.d. splits in the ratio of the resistances:
Watch out: connecting a load across R₂ puts it in parallel with R₂, lowering the combined resistance and therefore lowering Vout below the unloaded value. Always combine the parallel pair first, then apply the divider formula.
Tap an item on the left, then its partner on the right.
Quantities: magnitude + unit; six base units; prefixes T→f; check homogeneity
Vectors: F cos θ and F sin θ; equilibrium = zero resultant force AND zero resultant moment
Motion: suvat; v–t gradient = a, area = s; projectiles = independent horizontal and vertical motion
Newton: F = ma; third-law pairs act on different bodies
Momentum: p = mv; Ft = mv − mu; momentum always conserved, KE only in elastic collisions
Energy: W = Fs cos θ; ½mv²; mgΔh; P = W/t = Fv; efficiency = useful ÷ total
Electricity: I = Q/t; V = W/Q; R = V/I; R = ρL/A; V = E − Ir; potential divider VinR₂/(R₁+R₂)
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You have worked through Forces, Energy & Electricity for CCEA GCE Physics. 🎉
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Next: test yourself in the Evaluate stage Confidence Quiz, then lock it in with Verify.