Forces in Water

Year Level

Year 7 – Stage 4 (Physical World & Chemical World, Australian Curriculum)

Curriculum Links

Science Understanding

• ACSSU117: Change to an object’s motion is caused by unbalanced forces acting on the object.
• ACSSU151: The properties of the different states of matter can be explained in terms of the motion and arrangement of particles.

NSW Syllabus Outcomes

• SC4-PW1: Describes the action of unbalanced forces in everyday situations.
• SC4-PW2: The action of forces that act at a distance may be observed and related to everyday situations.
• SC4-CW1: Compares physical states of matter and explains their properties in terms of the motion and arrangement of particles.

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Lesson Duration

60 minutes

Class Size

25 students

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WALT (We Are Learning To):

• Understand that any object placed into water loses weight due to an upward force called buoyancy.
• Represent buoyancy and weight forces using appropriate force arrows.
• Predict how unbalanced forces affect motion in everyday contexts, especially when in fluids (water).

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Success Criteria:

• ✅ I can describe how weight changes in water.
• ✅ I can draw accurate force arrows showing buoyancy and weight.
• ✅ I can explain how these two forces interact when an object floats or sinks.

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Resources Required:

• Clear plastic tubs filled with water
• Spring scales (Newton meters)
• Range of objects (wooden blocks, metal bolts, plastic containers, rubber balls)
• Worksheets with diagrams for annotation
• Whiteboard and markers
• Printed force-arrow guides (dyslexia-friendly fonts)
• Stopwatch
• Towels or cloths for drying hands/objects
• Laptops or tablets (optional, for extension)

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Lesson Sequence

1. Kickstart: Predict & Wonder (10 mins)

Hook Question (on board):

"What happens to the weight of something when you put it in water?"

• Begin with a short class discussion.
• Show a metal bolt suspended on a spring scale in the air. Record the weight.
• Lower it slowly into a tub of water without touching the sides/bottom and show the reduced reading.
• Ask: “Has it lost mass? Why is it now ‘lighter’?”

Think-Pair-Share:

Students predict why the weight changes when submerged.

WALT Connection:
Explain today we’re learning about the force that makes things seem lighter in water — buoyancy.

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2. Core Activity: Measuring Buoyancy (25 mins)

Station Rotation – 3 Stations (8 mins each)
Split the class into 3 groups of 8–9 students. Each station has differentiated instructions and scaffolds.

Station 1 – Spring Scale Science

• Measure object weight in air and water
• Record difference
• Predict and explain using scaffolded worksheet

Station 2 – Diagram Labelling Task

• Use diagrams showing floating/sinking objects
• Students add force arrows for weight (down) and buoyancy (up)
• Arrows differentiated into small/medium/large thickness for Level 1–3 complexity

Station 3 – Everyday Object Analysis

• Given objects (e.g., life jacket, boat model, pebble), students sort into 3 categories:
  • Floats easily
  • Floats with effort
  • Sinks
  • Then discuss why each behaves the way it does in water

Extra Support (Differentiation):

• Use visuals and scaffolding page with sentence starters
• Colour-coded instructions
• Dyslexia-friendly fonts and printed diagrams
• Peer buddy systems set up for performing each task

Extension (Advanced Learners):

• Calculate approximate buoyant force (Weight in air – Weight in water = Buoyant force)
• Explore concept of water displacement using Archimedes’ Principle (simplified prompt provided on worksheet)
• Design a mini experiment: How does shape affect buoyancy? Option to compare spherical vs cuboid submerged items

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3. Consolidation: Whole Class Reflection (10 mins)

Force Diagram (Teacher-led):
Draw a boat floating in water on the board. Invite students to help draw force arrows for:

1. Downward weight
2. Upward buoyant force
   Discuss: “When are these forces balanced? When are they unbalanced?”

Mini Whiteboards (Formative Assessment):
Write or draw:

• One thing you learned
• One thing you’re wondering about
  (Individual reflection, shared in pairs)

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4. Exit Ticket (5 mins)

Distribute small slips of paper with the sentence starter:

“I now understand that buoyancy is…”
“I still have a question about…”

Collect on exit – used for informal assessment and next lesson planning.

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Differentiation Strategies

Learner Type	Strategy
EAL/D Learners	Visual aids, labelled diagrams, bilingual word banks where appropriate.
Students with Dyslexia	Use OpenDyslexic font worksheets, paired reading tasks, colour-coded notes.
Kinesthetic Learners	Hands-on practical stations, manipulating real-world items.
Advanced Learners	Extension tasks related to Archimedes’ Principle and complex predictions.
Visual Learners	Illustrated process cards, digital simulations (optional).

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Assessment Opportunities

• Observation during activities and discussions
• Accuracy of force arrows and explanation on worksheets
• Exit ticket reflections
• Formative feedback through mini whiteboard responses

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Follow-Up Ideas

Next lesson:

• Design Challenge: Create a foil boat that can hold the most marbles before sinking – apply knowledge of buoyancy, shape, displacement.
• Introduce connection to density and particle arrangement in solids, liquids, and gases (CW1 link).

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Keywords for Vocabulary Wall

• Force
• Buoyancy
• Weight
• Upthrust
• Balanced / Unbalanced Forces
• Float / Sink
• Arrow notation

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Teacher Reflection Prompt

After lesson, consider:

• Which activities allowed students to show deep understanding?
• Did all students engage meaningfully with the hands-on stations?
• What misconceptions about forces in water arose that need to be addressed next lesson?

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This lesson is fully aligned with Australian Science Curriculum (ACSSU117 / ACSSU151) and Stage 4 Physical and Chemical World outcomes, accentuating inquiry, hands-on learning, visual scaffolds, and deep conceptual understanding—all in a format ready to wow your students and colleagues alike.