Pressure in Fluids

Overview

In this lesson (Lesson 4 of 15) students explore how pressure in fluids depends on depth and how it acts on surfaces. Through guided demonstrations and data collection, students connect observations to the idea that fluids exert pressure in all directions.

Learning intentions

• Students will describe how pressure changes with depth in a fluid.
• Students will explain how pressure in a fluid acts on surfaces.
• Students will use simple evidence (observations and measurements) to support scientific claims about fluid pressure.
• Students will participate in safe, structured investigations and communicate results clearly.

Success criteria

• I can describe that deeper points in a fluid experience greater pressure than shallower points.
• I can explain that pressure acts on surfaces and can be measured/observed using simple tools.
• I can use my observations or collected data to support a claim about fluid pressure.
• I can communicate results using clear scientific language (e.g., depth, surface, pressure, all directions).

Curriculum links

• Understanding fluids and forces: pressure effects and factors that influence them.
• Inquiry and investigation skills: planning, conducting investigations, and processing evidence.
• Scientific communication: using data, observations, and explanations to support ideas.
• Nature of science: using evidence to build explanations.

Lesson structure (45 minutes)

1. 3 min — Launch & review

• Teacher prompts: “Last lesson we looked at how fluids flow. Today we ask: why do some objects sink or feel harder to move in liquids?”
• Students quickly share one prior idea about forces in fluids (no right/wrong answers yet).

2. 7 min — Model the driving idea

• Teacher demonstrates a sealed syringe/nozzle setup or a simple “pressure on a surface” demo (e.g., water poured onto different-sized surfaces using the same depth start).
• Class builds an anchor statement: “In a fluid, pressure increases with depth and acts on surfaces in all directions.”

3. 12 min — Investigation A: depth and pressure

• In groups of 3–4, students use a transparent container with several depth marks and a simple indicator method (e.g., holes at different heights with water jets, or a diaphragm-like cup with a consistent method to compare how far/strongly water moves).
• Students record what happens at different depths using a table: depth level → qualitative pressure indicator (e.g., stronger/weaker jet or indicator response).
• Teacher circulates for language support: “What changed? What stayed the same? What does your evidence show?”

4. 10 min — Investigation B: surface area and pressure (controlled comparison)

• Teacher sets up a comparison where students test how changing surface area affects the force experienced while keeping depth/pressure condition controlled as much as possible (e.g., same depth, different piston areas, or two coverings at the same depth responding differently).
• Students complete a short comparison: “When surface area changes, how does the evidence change? Does pressure behave differently if the depth is the same?”
• Emphasis: pressure relates to depth; total force depends on surface area.

5. 8 min — Whole-class sense-making

• Groups share one key observation from each investigation.
• Teacher prompts students to connect to claims: “Claim: pressure depends on depth. Evidence: … Reasoning: because …”
• Address misconceptions: “Bigger surface gets more total force, but pressure is determined by conditions in the fluid.”

6. 5 min — Exit ticket (assessment for learning)

• Students answer: “Explain how pressure changes at two different depths. Then state what happens when pressure acts on a surface (include direction or where forces occur).”
• Collect to check vocabulary accuracy and conceptual understanding.

Resources

• Transparent container(s) with depth marks (e.g., 1–2 large tanks or containers)
• Water source and measuring tools (ruler, measuring jug)
• Holes/ports for depth comparison demo (or prepared equipment for jet/response comparison)
• Simple seals, tubing, or safe indicators for comparing pressure effects
• Data recording sheet with tables for depth and surface comparison
• Safety glasses for students
• Group roles cards (materials manager, recorder, safety officer, reporter)
• Sentence frames for ESL learners (e.g., “At greater depth, I observe… Therefore, pressure…”, “Pressure acts on… in all directions”)

Assessment

• Observation checklist during investigations: correct recording, safe behaviour, using scientific language.
• Formative questioning: “What is your evidence? What changed? What stayed the same?”
• Exit ticket responses checked for: depth-pressure relationship, pressure acting on surfaces, and clear reasoning.

Differentiation

• Support for ESL learners:
• Provide sentence starters for claims/evidence/reasoning.
• Pre-teach essential words with visuals (depth, surface, pressure, direction, greater/less).
• Allow drawing-based evidence (e.g., labelled diagrams) in addition to written statements.
• Support for students needing scaffolding (SEN):
• Provide partially completed tables and a model example of a “claim-evidence-reasoning” paragraph.
• Assign a role aligned to strengths (e.g., measurements, drawing, or timing) while rotating responsibilities.
• Extension for advanced students:
• Challenge: predict outcomes if depth increases by a larger amount and justify using proportional reasoning (qualitative or with simple scaling).
• Ask for a refinement: identify one limitation of the demonstration and suggest an improvement.
• Accessibility and classroom routines:
• Ensure clear step-by-step instructions posted visually.
• Reduce cognitive load by having students focus on one variable at a time during each investigation.