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NSW Syllabuses

STEM Stage 2 – Activity 2

Sailing away

model boat

Description of activity

Students design and make a vessel, with a sail, that will transport an object across a body of water.

This activity takes two lessons:

  • investigate floating and sinking and designing a vessel
  • make, test, evaluate and modify the design.


Students have prior knowledge about objects that sink and float. They can measure mass with digital scales, length in cm and mm and can determine area in cm2.

Students will apply their engineering skills and their understanding of floating and sinking. A sailing vessel may be built out of any materials that you (or your students) choose. The size of the object/container that will become the vessel should be standard, eg no larger than a carton of milk or a small plastic container. The criteria are that the vessel must support sails and an object of a given weight (eg 100g) and that the vessel is able to float across the body of water. In the final demonstration of the design solution, students will place the vessel into the water and blow it across to the other side with a fan.



ST2-4WS investigates their questions and predictions by analysing collected data, suggesting explanations for their findings, and communicating and reflecting on the processes undertaken
ST2-5WT applies a design process and uses a range of tools, equipment, materials and techniques to produce solutions that address specific design criteria
MA1-1WM describes mathematical situations and methods using everyday and some mathematical language, actions, materials, diagrams and symbols
MA1-2WM uses objects, diagrams and technology to explore mathematical problems
MA1-3WM supports conclusions by explaining or demonstrating how answers were obtained

Knowledge and understanding

ST2-7PW describes everyday interactions between objects that result from contact and non-contact forces
ST2-16P describes how products are designed and produced, and the ways people use them
ST2-13MW identifies the physical properties of natural and processed materials, and how these properties influence their use
MA2-10MG measures, records, compares and estimates areas using square centimetres and square metres
MA2-11MG measures, records, compares and estimates volumes and capacities using litres, millilitres and cubic centimetres
MA2-12MG measures, records, compares and estimates the masses of objects using kilograms and grams



  • Materials that could be used for boat construction, eg polystyrene, paper, aluminium foil, plasticine, balsa wood, other wood, cloth, skewers, etc (teacher choice)
  • Scissors, sticky tape, string, plastic bottles
  • Object to be transported in the vessel, eg marbles, nuts and bolts
  • Storage crate, bucket, trays, wading pool or pond containing water

Work, health and safety

Check relevant Work, health and safety guidelines.

Evidence of work for assessment purposes

  • A design plan showing a labelled diagram of the design with notes justifying modifications made to develop the final design solution
  • A visual record of the vessel – photo (top view and side view) or video of the test procedure

STEM teaching and learning activities

  • Students identify materials that float or sink. Share and discuss student ideas on floating and sinking.
  • Students compare the areas of regular and irregular shapes by informal means.
  • Students measure the area of irregular shapes using a square centimetre grid overlay.
  • Students compare the surface areas of different objects using familiar metric units of area, eg cm2 or m2.
  • Students compare the volumes of two or more objects by marking the change in water level when each is submerged in a container.
  • Students use scales/pan balances to measure masses and record masses in kg or g.
  • Students design a vessel that fits the criteria set and record the characteristics of this vessel, including materials, shape and dimensions. See carrying out a design plan.
  • Students make and test their designed vessel. If any modifications are needed, students record these and the reasons for the changes on their design plan. This process will continue until the vessel fits the criteria set.

Vocabulary list

Scales – apparatus to measure weight/mass (not fish scales or the scale on maps)
Mass – the amount of matter in an object
Gram, kilogram – measures of mass
Centimetre, millimetre, metre, kilometre – measures of length
Square centimetre, square metre – measures of area
Millilitre, litre – measures of liquid volume
Cubic centimetres, cubic metres – measures of volume
Force – a push, pull or twist
Gravity – non-contact force
Buoyancy – the upward force that enables objects to float in water
Resistance – a contact force acting in the opposite direction of a force, often provided by water or air
Displace, displacement – the weight or volume of fluid that is moved by an object floating or sinking in the fluid
Float – to stay on the surface of or suspended within a liquid
Sink – to go below the surface of a liquid
Evaluation – how well your solution fits the criteria
Justification – support your ideas

Key inquiry questions

Is it only the material that an object is made from that determines whether it will float or sink?
There are many factors that determine whether an object floats or sinks, eg shape, surface in touch with the liquid, the liquid in which an object is placed.

How does gravity relate to floating and sinking?
The force of gravity pulls objects towards the earth. Water resists this downward force by providing a force in the opposite direction (buoyancy). The mass of an object determines the downward force on the object. The area of the water that is in contact with the bottom of the object and the mass of water displaced provides an opposing force to the downward force. If something floats on water, the downward force (gravity) is equal to the upward force (buoyancy).

The following factors affect buoyancy:

  • material the object is made from
  • shape of the object
  • mass of the object.

What is the relationship between mass and volume?
The mass of an object is the amount of matter it contains. The volume of an object is the amount of space it occupies. Thus, objects of the same mass may have different volumes, eg an amount of plasticine will occupy different volumes if scrunched into a ball or smoothed out. The plasticine ball may sink whereas the flat piece of plasticine can be moulded to displace enough water to float.

How will you record the details of your structure so that you or someone else can build it?
Encourage students to record their design ideas with sketches and annotations. They may wish to take photos and label their photos. This may be done using computer software.

What information would be important to make this an accurate record?
Diagrams showing shapes and measurements. Some students may be able to create scale drawings.

What modifications have you made to your design plan? Why did you feel they were necessary?
Testing, making modifications and retesting provide important learning opportunities. Perceived 'failure' should be taken as opportunities to analyse why the structure did not work. Then productive modifications can be made. If students are able to complete the task without refinement, the task is not challenging enough or the product does not do everything it should be doing.

What do you think is preventing your vessel from doing what it needs to do? How can you change it?
Trial and error is encouraged and failures are celebrated. It is through the failures and resulting modifications that students learn to work technologically. Students should use the design criteria and results from testing to explain the changes and how they arrived at the solution.

Additional information

The following statements outline some common preconceived ideas that many students hold, which are scientifically inaccurate and may impede student understanding.

Heavy things sink and light things float, or big things sink and small things float.
The mass of an object is important but it is not the only consideration when considering buoyancy. The volume of the object and the surface area in contact with the water affect the mass of water displaced and therefore affect buoyancy. So, for example, a small pebble may sink but a large ocean liner will float.

Things that might sink in a small amount of water would float in a larger amount of water
For example, an object might sink in a tray of water, but it will float in a bathtub of water.

This challenges the concept of buoyancy – the upward thrust of water, ie the more water there is, the greater the upthrust. This misconception can be easily tested and shown to be unsupported by evidence.

Support materials

Adjustments for the diversity of learners

The materials that you provide will scaffold this task. Providing buoyant materials will make the task easier. Limiting the choice or quantity of materials will make the task more difficult.

Rewards may be given for most elegant design, fastest vessel and/or the vessel that can carry the heaviest weight.

Some students will be moving towards an understanding of density and/or the effects of surface area and displacement of water on flotation.

Do all materials of the same size and shape float? What are the differences between these materials?


In this STEM activity, your students will have explored the concepts of density (to be introduced officially in the Science Stage 4 and Biology, Chemistry and Physics Stage 6 courses), and surface area (which later helps explain how materials are transported across membranes in Biology Stage 6). They have also been challenged to develop the attributes of perseverance and resilience.

The following concepts are not considered to be a part of Stage 2 understanding. However, there will be a number of students who will already have an experiential understanding or are developing an understanding of three significant ideas around floating and sinking. These ideas are those of density, surface area and surface tension.

Density is a property of matter. It is the relationship between the mass of a substance and the volume it occupies. Density can be calculated mathematically by finding the mass of an object (by weighing it) and finding the volume of that object (either by measurement or by displacement).

Density = Mass/Volume

It is density that determines floating and sinking, not just mass or volume. Water, at room temperature, has a density of 1 gram/cm3. The density of ice is 0.9167 gram/cm3 at 0°C. Because the density of ice is lower than the density of water, ice cubes float on water. Because the density of ice is only slightly lower than that of water, ice does not float completely on the surface of the water, but lower down. This also explains why approximately 90% of the mass of icebergs float below sea level.

Surface area can be described as the area covered by every surface of an object. Surface area of regular and irregular objects can be measured by using grid paper.

Area of regular objectarea of irregular object

If two objects of the same density are placed on the surface of water, the object with a larger surface area is more likely to float. This idea can be investigated by providing students with equal masses of plasticine and asking the students to test different shapes and their floating behaviour in water, eg test plasticine in the following three-dimensional shapes: sphere, cube, cylinder, cone, flat quadrilaterals.

Surface tension is often regarded as a ‘film’ that forms on the surface of liquids. It is due to the forces of attraction between (in this case) water particles. This attraction is the result of the fact that water is a polar molecule (has a positive and negative side) and surface tension enables some things to float on water if they are placed carefully on the surface. For example,

a paper clip or water strider or dew drop.

paper clip Water striderDew drop