Early Stage 1 – STEM Activity 12

Floating bridge

A bridge which floats on the water, crossing from one bank of a river to another. The bridge consists of a path that people can walk on, a hand rail and safety mesh on both sides of the pathway running along the length of the pathway.

Description of activity

Students design a bridge that floats so the Three Billy Goats Gruff can cross the river and be free of the troll.

This activity will take approximately 90 minutes for:

research
experiments on floating and sinking, design
construction and testing.

Context

Students will have identified the basic needs of living things, including food. They understand that materials have observable properties, eg can float or sink, and that bridges are designed to suit the purpose of spanning one place to another to enable a safe crossing.

Students can use the language of mass when comparing objects by using hefting. They understand that bridges need to support varying masses.

Students will produce solutions to enable the Three Billy Goats Gruff to safely cross the river over a floating bridge in order to get to their food. (A floating bridge has no room for a troll to reside beneath it!)

Outcomes

Skills

STe-4WS explores their immediate surroundings by questioning, observing using their senses and communicating to share their observations and ideas
STe-5WT uses a simple design process to produce solutions with identified purposes
MAe-1WM describes mathematical situations using everyday language, actions, materials and informal recordings

Knowledge and understanding

STe-8NE identifies the basic needs of living things
STe-9ME identifies that objects are made of materials that have observable properties
STe-10ME recognises how familiar products, places and spaces are made to suit their purpose
MAe-12MG describes and compares the masses of objects using everyday language
ENe-1A communicates with peers and known adults in informal and guided activities demonstrating emerging skills of group interaction

Resources

Materials to build a demonstration bridge, eg building blocks and plank
Troll-like soft toy or puppet
Variety of materials that float and sink
Variety of construction materials, natural and/or made, eg bark, sticks, leaves, plastic plates, cardboard, sticky tape, straws, small PET bottles with lids, corks, polystyrene foam pieces, paddle-pop sticks
Small plastic toy goats or handmade clay goats to represent the Three Billy Goats Gruff
Small plastic bags of sand or pebbles to tape to the goats to provide additional mass
Large tub of water, eg water play tray or smaller tubs of water, eg tote tray

Work, health and safety

Check relevant Work, health and safety guidelines.
Be aware of water spills and slippery areas.

Evidence of work for assessment purposes

A photograph of a model of a floating bridge that floats and can hold the weight of at least the heaviest toy billy goat.
A record of student’s explanations for their design choices.

STEM teaching and learning activities

Read, tell or watch an animation of the story of the Three Billy Goats Gruff. Discuss the story, focusing on the goats’ need for food and their need to cross the river to access it.
Observe a variety of bridges in and around the school grounds, eg railway, foot bridges, on play equipment. Discuss similarities and differences in the design. Discuss what it spans, what travels across each bridge, and whether or not a troll could live under it. Highlight features of bridges that suit the purpose of the bridge, such as:
- height off the ground/water
- supports
- width and strength of path.
Introduce a troll-like soft toy. Discuss design modifications of the bridge, so the troll cannot fit under the bridge, eg a floating bridge that has no space under it so a troll could not make its home there.
Introduce the concept of floating. Observe floating and pontoon bridges. Identify design features, eg floating drums, railings and pathway.
Students predict, test and observe the floatation of a variety of objects. They sort the objects into two categories: those that sink and those that float. Record these in a table.
Describe the three billy goats that crossed the bridge. Use the comparative language of mass to describe them: lightest, lighter, heavier, heaviest. Which one did the troll want to eat? Why?
Students use hefting to compare the masses of the toy billy goats (with taped on pebbles) and make statements such as, ‘this goat feels heavier than this one’.
Students, in groups, design a model of a floating bridge that can support the mass of at least the heaviest billy goat. Determine the span of water that the bridge must cross.
Students choose the materials they wish to use to build the bridge using both natural and made materials.
Students construct the bridge. This could be undertaken outdoors or indoors.
Students test their models on water and explain their design decisions. Take a photograph of each bridge with heaviest toy goat on it and record each verbal explanation for assessment purposes.

Vocabulary list

Bridge – a structure that spans an area, eg a river, gorge, roadway
Buoyancy – the upward force that enables objects to float in water
Flat – having a level surface
Float – to rest on the surface of a liquid
Heavy, heavier, heaviest – comparisons of great weights
Hefting – testing the weight of an object by lifting and balancing it, eg in each hand
Light, lighter, lightest – comparisons of lesser weights
Mass – the amount of matter in an object; a quantity
Sink – to go below the surface of something, especially a liquid
Weight – the effect of the force of gravity on a mass

Key inquiry questions

What is the main purpose of a bridge?
Discuss the concept that things may have a variety of purposes, but there is usually one main purpose which determines the basic characteristics of the object or structure. Other features may be considered important or aesthetically pleasing, but do not necessarily enhance the purpose/usefulness of the structure.

How do bridges suit their purpose?
Students examine and describe the features of bridges. Students may group the features according to those that are essential to the main purpose vs those that are non-essential (but often desirable).

Which objects float?
Students predict, test and observe the buoyancy of a variety of objects.

Which Billy Goat Gruff has the greatest mass?
Students use hefting to compare the weights of toy goats and use the language of mass to compare the goats. Discuss indications of a greater mass, eg ‘heavier footsteps on the bridge’.

How can a floating bridge help the billy goats get to their food and keep them safe from the troll?
Encourage students to make suggestions and justify their choices.

Additional information

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

Belief that: larger things are heavier; smaller things are lighter; the same size and shape has the same mass
Students need to have experiences with hefting large light objects, eg an inflatable beach ball and small heavy objects, eg a cricket ball and objects of the same size and shape but different weights, eg golf ball and ping-pong ball. When being introduced to hefting, students should compare two objects that have significantly different masses.

Heavy objects sink and light objects float
Students need lots of experiences exploring, manipulating, and testing objects. Students can explore floatation of various shapes using modelling clay, eg as a ball, as a flat shape, etc.

Floating means that the object must be completely on top of the water
Reinforce the correct definition that objects are floating even if parts are submerged, eg the hulls of ships.

An object floats higher in deeper water
Demonstrate that depth of water has no impact on floating. Students can also test this for themselves.

Support materials

YouTube video: The Three Billy Goats Gruff
Float and Sink: game by BBC
Build the Bridge: game
YouTube video: What’s heavier than a lunch box?
YouTube video: Pontoon Bridge Construction watch the army build a pontoon bridge

Diversity of learners

For additional support

Assist students in the selection of materials and guide them through the design process.
Assist students to make connections between properties of materials, mass and design features.
Students view their peers’ models and reflect on their own design. They make adjustments if desired.

For extension

When describing the three billy goats, extend the description to challenge students to determine the number of billy goats, ears, horns, eyes, legs, hoofs, tails etc.
Encourage students to draw and label their planned design before constructing it. They explain their design to their peers and make amendments following discussion.
Students compose a recount of one of the goats describing the bridge and living safely away from the troll.

Review

In this STEM activity your students have recognised that materials have observable properties. This concept is enhanced in later Stages and leads to the Particle Theory of Matter that will be more fully investigated in Science Stages 4 and 5.

Students have applied their understandings through the design and construction of a floating bridge as a purpose-built structure. Students will further examine how the purpose of a product influences its design. This concept is essential understanding for Technology (Mandatory) Stage 4 and the concept of ‘Structure and Function’, which underlies many biological studies.

Working collaboratively, students have manipulated natural and made materials. They have used creative thinking and problem-solving skills and have provided verbal explanations to justify their design decisions.