Crane’s Balance

2- Analysis of operation and specifications
Authors : Hélène Merle(plus d'infos)
Muriel Guedj(plus d'infos)
Summary :
The pupils analyze the role of different fixed or mobile cranes and become aware of the technical constraints in the construction of the scale model.
Publication : 1 February 2004
Objectives :
Notional goals: Appropriate specifications for the construction of a scale model of a crane. Observation of an object. Making assumptions about the operating principle. Objectives of know-how (Practical skills): describe with precision; make sketches, diagrams. Vocabulary: charge, mass, translational motion, rotation (if needed).
Material :

For each group of pupils
- photos of a crane or videotape
- toy crane
- reports of a possible visit of a construction site

Download the board of 9 photos (.pdf)

Specialized sites:

A French manufacturer : Potain

A Belgian manufacturer : Sarens

Toy cranes : Meccano

Pedagogical approach



1. Reminders (5 min)

Announcement of the sequence’s goal: making a model of a crane.

Prior to this meeting, the material has been provided by the teacher and/or pupils in the classroom. A visit was organized to a construction site. Otherwise, the attached file with different types of cranes or the pages of websites can be used.

2. Collective analysis of the provided materials (20 min)

Cranes are presented to pupils.

“We will build a model of a crane together, for this we will have to determine what is common to all these cranes. Describe the movements made by the crane when it is moving objects.”

The various movements are analyzed. The vocabulary is specified as and when required (jib, counter-jib, mast, stand, cables, hooks, counterweight).

The collective results of this analysis are written on the board for the completion of the record.
Prepare either small pictures of individual cranes or enlarged pictures to display.
The images provided can also be viewed on computers in the classroom if the hardware allows it. Responses expected:
- rotation of the jib (horizontal movement, circular)
- lifting (vertical translation and weight constraint)
- translation of the carriage (linear horizontal displacement)

3. Written record

Children change their initial individual or group drawings and verify the inclusion of different movements.
The written record is adapted according to the discussion that has preceded it. Possible example
“The crane is a construction machine that can lift and move loads along a linear and/ or circular path.”

Word from La main à la pâte

The photos show a metal structure with geometric shapes (mostly triangles). The materials available to the children do not permit copying this metal structure.

To permit the children make abstraction, trace pictures of cranes, and then color the main rooms.

On the contrary, to deepen this aspect, some teachers propose the construction of bridges using A4 paper sheets either rolled or folded and assembled  using adhesive tape.

Bridge made by M, Guizol’s pupils of 3rd Cycle, École de Maisse (91) June 2001


Lors de l'étude des mouvements de la grue, j'avais abordé avec mes élèves l'idée de la zone au sol dans laquelle la charge peut-être déposée. (J'avais utilisé pour cela une vidéo d'une grue en action). Il s'agissait là d'approcher l'idée de surface, en combinaison avec le travail sur la fonction de cet outil. Cette surface, que les élèves peuvent aisément dessiner, est une couronne, résultante de la combinaison des mouvements circulaire et rectiligne. Les difficultés qu'ils ont alors rencontrées et surmontées m'ont convaincu qu'il s'agissait pour eux d'un vrai problème dont la solution, entrant dans le champ des mathématiques, se construit dans l'interdisciplinarité.