LuduminaFM-18 · FM-U6 · Planned
Liquid depth, upthrust, floating and sinking
Learning objectives
Calculate liquid pressure changes; explain upthrust and buoyancy using pressure differences.
8463 §§4.5.5.1.2 / No Trilogy counterpart
DfE single-science pp.35–37 / Combined pp.30–32. Evidence checked 30 September–1 October 2026. Skills: WS1.2,3.6; MS3b,3c,4a.
Explanation
Greater liquid depth means a taller liquid column above a point. A submerged body therefore has greater pressure beneath than above, producing upthrust. Floating equilibrium requires upthrust to balance weight; it does not remove gravity.
Concepts, equations and units: p=hρg for pressure due to liquid column; Pa, m, kg/m³, N/kg; upthrust N; total pressure may include atmosphere.
Prediction, demonstration and game exercise
Predict, observe, explain
Place pressure sensors at several depths and on upper/lower faces of a block.
Planned learner game exercise
Choose a vessel and cargo density to float; reconcile upward/downward forces and depth data.
Independent practice
Two pressure-difference calculations and annotated floating/sinking explanations.
Original practice example · Separate Physics Higher
Find water-column pressure 2.0 m deep using ρ = 1000 kg/m³ and g = 10 N/kg, excluding atmosphere.
Show working and model answer
Working / reasoning
p = hρg = 2.0 × 1000 × 10.
Answer
20,000 Pa due to the water column.
Exit check and success criteria
Both values correct and upward resultant linked to greater pressure below; floating force balance correct.
During practice, compare the prediction with evidence and give an error-specific prompt. The exit item uses a fresh context or fresh values, answered independently.
Misconceptions, practical links and mastery
Check these misconceptions
Use total pressure as liquid-only contribution; floating requires no weight; larger density always means larger upthrust independent of displaced volume.
Practical preparation
Optional flotation/pressure-column demonstration.
Virtual preparation and revision only. Required hands-on activities and school records remain separate.
Proposed mastery
0: not yet evidenced. 1: supported. 2: independent exit criteria met. 3: successful changed-context transfer. Advance at 2; revisit with fresh retrieval. These are not GCSE grades.