G2 Science Physics Formula List
Equations for G2 Science Physics, with units, graph rules, conditions and examples at the K223 / K224 course depth.
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Reference for the Physics component of G2 Science (K223 / K224, 2027). The equations below support this component; Chemistry and Biology have their own subject content. Use consistent units and read the conditions before calculating.
Before substituting
Use m, kg, s, A, V and J unless an equation explicitly uses another compatible unit. 1 cm² = 10⁻⁴ m² and 1 cm³ = 10⁻⁶ m³. Symbols are local: V means volume in density calculations and voltage in circuits; W can mean weight or work.
Measurement and unit conversion
| Relationship | Symbols and units | When to use it |
|---|---|---|
| ρ = m/V | Density ρ in kg m⁻³; volume V in m³ | Use the object’s mass and the volume it occupies. |
| correct reading = observed reading-zero error | All readings in the same unit | Zero error is signed; subtracting a negative error increases the reading. |
| gradient = Δ y/Δ x | Units of the vertical axis divided by units of the horizontal axis | Select two well-separated points on a best-fit line, not necessarily two raw readings. |
Useful conversions: 1 cm = 10⁻² m, 1 cm² = 10⁻⁴ m², 1 cm³ = 10⁻⁶ m³, 1 g = 10⁻³ kg and 1 km/h = 1/3.6 m/s. Prefixes multiply the unit: nano 10⁻⁹, micro 10⁻⁶, milli 10⁻³, centi 10⁻², kilo 10³, mega 10⁶ and giga 10⁹.
Motion
| Relationship | Symbols and units | When to use it |
|---|---|---|
| average speed = total distance/total time | Distance in m; speed in m s⁻¹ | Include all travel time, including any stops. |
| a = (v-u)/t | Initial speed u, final speed v in m s⁻¹; a in m s⁻² | Average acceleration for motion in one direction; positive means an increase in speed. |
Graphs: gradient of a distance–time graph = speed; gradient of a speed–time graph = acceleration for motion in one direction; area under a speed–time graph = distance travelled. Read the axis labels before deciding what gradient or area represents.
Forces and pressure
| Relationship | Symbols and units | When to use it |
|---|---|---|
| W = mg; g = W/m | Weight W in N; g in N kg⁻¹ | Use the field strength at the object’s location. Near Earth, use the question’s value (often 10 N kg⁻¹ at secondary level). |
| Fᵣₑₛᵤₗₜₐₙₜ = ma | Resultant force in N | Fixed mass; use the vector sum of all forces on the chosen body. |
| p = F_⊥/A | Pressure p in Pa; area A in m² | Force is normal to the surface; 1 Pa = 1 N m⁻². |
Energy and power
| Relationship | Symbols and units | When to use it |
|---|---|---|
| W = Fd | Work W in J; displacement d in m | Constant force; d is displacement in the force’s direction. |
| Eₖ = 1/2 mv² | Kinetic energy in J; speed v in m s⁻¹ | Use speed squared; doubling speed quadruples kinetic energy. |
| Δ Eₚ = mgΔ h | Change in gravitational potential energy in J | Near Earth in a uniform gravitational field; state the height reference. |
| P = E/t | Power in W; energy in J; time in s | Average rate of transfer; 1 W = 1 J s⁻¹. |
| η = E_useful/Eᵢₙₚᵤₜ | Efficiency η has no unit | Use energy or power consistently; multiply the ratio by 100% for percentage efficiency. |
Waves
| Relationship | Symbols and units | When to use it |
|---|---|---|
| v = fλ | Speed v in m s⁻¹; f in Hz; λ in m | The speed and wavelength must be in the same medium. |
| f = 1/T | Period T in s | One complete oscillation. |
| d = vt/2 | Echo distance d in m | Time is for the outward and return journey. |
Electricity and circuits
| Relationship | Symbols and units | When to use it |
|---|---|---|
| Q = It | Charge Q in C | Constant current; 1 C = 1 A s. |
| V = E/Q; ε = E_supplied/Q | p.d. V and e.m.f. ε in V | Distinguish energy transferred by a component from energy supplied by a source per unit charge. |
| R = V/I | Resistance R in Ω | Use p.d. across and current through the same component; this definition does not imply constant R. |
| R ∝ l/A | Wire length l in m; area A in m² | Compare wires of the same material at the same temperature. |
| Rₛ = R₁ + R₂ + … | Equivalent resistance in Ω | Resistors in series: same current, p.d.s add. |
| 1/Rₚ = 1/R₁ + 1/R₂ + … | Equivalent resistance in Ω | Resistors in parallel: same p.d., branch currents add. |
| P = VI = I²R = V²/R | Power in W | V and I describe the same component; substitute V = IR to obtain the last two forms. |
| E = Pt = VIt | Energy in J | Constant power/current and p.d.; use seconds for J, kW and hours for kW h. |
| cost = E_(kW h) × price per kW h | 1 kW h = 3.6 × 10⁶ J | A kilowatt-hour is energy, not power. |
Radioactivity
| Relationship | Symbols and units | When to use it |
|---|---|---|
| N/N₀ = (1/2)^(t/t_(1/2)) | Remaining undecayed nuclei N; half-life t_(1/2) | For a single radioactive isotope; use the same time units. Activity follows the same fraction. |
| net count rate = measured count rate-background count rate | All rates in the same unit | Subtract background before comparing half-lives; keep source–detector geometry unchanged. |
Quick application: energy cost
A 1.5 kW appliance runs for 2.0 h. It uses E = Pt = 3.0 kW h. At 30 cents per kW h, the cost is 3.0 × 30 = 90 cents. Using hours is appropriate here because power is in kW and the tariff is per kW h; use seconds when calculating joules.
Scope and next step
This course does not require the Pure Physics specific-heat-capacity, specific-latent-heat or transformer-turns calculations. G2 also does not require a quantitative moment equation or refraction calculations. Half-life questions can be solved by repeated halving or by reading a decay graph.
Open the course hub and use the relevant topic check to practise without this sheet.