Crane’s Balance

5- Testing the models
Authors : Hélène Merle(plus d'infos)
Muriel Guedj(plus d'infos)
Summary :
The teacher encourages pupils to conduct a technological analysis of the production: the fixed and mobile parts, type of guidance involved, issues related to friction, importance of the function, etc. The problems brought up can lead to organizing additional meetings for technical solutions. To do this, each crane is tested with three different masses.
Publication : 1 February 2004
Objectives :
Notional objectives: understanding that a crane’s load is limited. Conditions for balance (setting the counterweight when lifting and moving a mass)
Material :

Per child
an experiment notebook
Per group
series of three masses to lift, while remaining within the possible limits for each completion (crane).
 

Pedagogical approach
 

1. Collective talk
 

The teacher presents the challenge of the session. It is to verify:
- That the crane meets the specifications (are the two movements possible?)
- That it is capable of lifting.

 

2. Group work

Each group performs various tests. Eventually, the pupils are encouraged to further ballast their counterweight or move it to the end of the jib.

3. Collective presentation

Each group performs a test in front of the classroom.
Critical analysis of the  models: we will focus on the two movements (rotation of the jib and translation of the cable) and the balance of the crane. 

4. Conclusion

The teacher provides pupils with a load of heavy weights, in order to unbalance the cranes. Pupils will be led to reflect on ways to improve the balance.
A comparison of the models may reflect the importance of several factors in balance: size of the base, mass and position of the counterweight, position of the load on the mast.
These comments will be recorded by the teacher as appropriate hypotheses to test in later sessions, if these problems have not been addressed.


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