Early Simple Machines Set

Crossing Crocodile River

Applying knowledge and skills related to structures, stability, measuring, and fair testing.

30-45 min.
Grades 1-2

The Problem

(5-10 Minutes)

Sam and Sara are on a jungle hike when they come to a fast-flowing river. They can see several crocodiles swimming in the river. Sam and Sara need to cross the river.

Can you help Sam and Sara get across the river safely?


Design Brief

(3-5 Minutes)

Design and make a safe and strong bridge that:

  • is at least 4 in long without touching the water
  • is at least 8 in above the water
  • supports the weight of at least Sam and Sara

Fair Testing and Fun

(10-15 Minutes)

  • Is the bridge 8 in long or even longer?
    Measure with a ruler or with the LEGO® DUPLO® box lid, which is 10.5 in wide. The longer, the better.

  • Is it at least 4 in above the water?
    Measure it and see.

  • Is it safe?
    Take the Sam and Sara models for a walk across the bridge.
    Can Sam and Sara walk on the bridge at any place without falling through holes or gaps?

  • How much weight can it carry?
    Where might the weakest place be? In the middle! Start with Sam in the middle, add Sara.
    Still OK? Then keep adding more weight (e.g. bricks) until it breaks! The more weight it can carry, the stronger the bridge.


Extra Challenge

(10-15 Minutes)

Design a boat that can go under your bridge and sail down the river.

Teacher Support

Students will be able to apply knowledge and skills around:
The framework of structures and how to make them stable and able to support loads
Solving problems from a specific design brief

Disciplinary Core Ideas: Physical Science

1 MS-PS2 Motion and Stability: Forces and Interactions

Crosscutting Concepts
Structure and function
Stability and change

Science and Engineering Practices
Asking questions and defining problems
Developing and using models
Planning and carrying out investigations
Analyzing and interpreting data
Using mathematics, Informational and Computer Technology, and computational thinking
Constructing explanations and designing solution
Engaging in argument from evidence
Obtaining, evaluating, and communicating information

Common Core State Standards for Mathematics
Mathematical Practice

MP1 Make sense of problems and persevere in solving them
MP2 Reason abstractly and quantitatively
MP4 Model with mathematics
MP5 Use appropriate tools strategically
MP6 Attend to precision
MP7 Look for and make use of structure

Measurement & Data
K.MD.A / 1.MD.A / 1.MD.C / 2.MD.A / 2.MD.D

Writing Standards
W.K.2 / W.1.2 / W.2.2

Speaking and Listening
SL.K.3 / SL.K.6 / SL.1.3 / SL.2.3 / SL.2.4