# Aprendizaje Activo: Puentes con palillos

A good way to learn is “doing”. The group of educational innovation VGG (Visual Graphics Group) the UPM develops educational experiences in which the student is the central element of learning.

Este año, teachers Rua José Jaime María Jesús Casati Armesto and Calzada has continued a practice that encourages sympathetic learning geometry of polyhedra, linking other subjects such as structural design: Building a toothpick bridge to verify its breaking load.
This educational model is documented in “Methodologies active as spatial vision improvement

The enthusiastic participation of our students has even led them to photograph the experience, and have seen some videos on youtube you can see the end of this article.

Here some photos, and the statement that they have been provided to students. The videos are worth.

 Bridge with chopsticks
Practice Statement

### Target:

Students, as part of the ongoing evaluation of teamwork, design and build a bridge for a light resistant equal to the length UNE A4 format ( L = 297 mm), using only materials as round toothpicks and white glue fast drying. Chopsticks are provided by the teacher, the latter being of 68,3 mm long, than they sell in Lidl in beakers 400 units. The resistance of the bridge is determined by dividing the load which is capable of supporting the weight of the bridge.

### Bases:

PARTICIPANTS: Students of the subject, part of teams of four. Each student in a team and each team a bridge.
DATES: Registration until Friday 16 January at 12:00. For the convenience of the equipment balance, the three last teams to register could be composed with three people, passing the fourth member to reinforce the team incomplete. Delivery and testing carried out in class, Friday 23 January at 9:00.
GEOMETRY:
• The upper bridge must allow continuous horizontal surface.
• The upper must have an area of ​​load bearing at least 18 cm x 6 cm, so that it can be placed on the weight to be supported.
• The maximum width of the bridge and its maximum depth is 2L / 3
• The bridges must meet a maximum height above the plane of the supports of 2L / 5.
MATERIALS:
• The means of attachment of the chopsticks should be white carpenter glue fast drying. It is the material that allows working with health and safety, so it is as binding as specified chopsticks.
• Chopsticks can not receive any treatment or reinforcement, tail can only be on their toes and allowed no duplicate, cut them or them thin.
• In the event of a suspected breach, Each team may request a test to verify that at least you can draw a stick intact in only one of its competitors. As a result of previous requests and perceptions, teachers may require proof to each of the contestants. The verification is to introduce the water-extreme nodes (or cotton swab) so that one could remove said stick.
BANS:
NO can be reinforced with glue structure elsewhere than the tips.
NO bridges can be painted, or be varnished, sprayed or submerged in any substance that changes its resistance.
None of superglue, loctite, silicone, etc..
NOT can stick toothpicks in the sides (the use chopsticks Doubles, triples, etc.).

### Test development:

#### to) Preliminary assessment and documentary, four:

Before turning to the endurance test shall be verified geometrical conditions shown in the accompanying drawing. (Fig. 1)
All teams must submit documentation by the model that describes:
Projections bounded dihedral or sketch
Photography
Anticipating the action of loads and the first break in two bars of the bridge.
It shows the example of the attachment, corresponding to the model is provided as a reference for note five out of ten top at the resistance.

#### b) Resistance Test, six points:

• The bridges are placed on supports between two tables, are separated by 297 mm (L). The heavy material ortoédricos packages consist of 1 liter of juice (attributed to the extent of 1 Kg), starting from 1 package, which will increase the 1 in 1.
• A team representative concerned affixed in the weighing load 1 kg, minimum weight to bear. We will add one by one weights 1 kg successively until the bridge lose its integrity. The bridge must support each of the weights increased a minimum of 5 seconds. Be considered for calculating the weight supported immediately before breaking. The total time available per team is five minutes.
SCORE:
• The bridge that gets the most weight ratio of dead weight supported and would get a 10 in this part of the test.
• The model given by the teachers, subjected to identical criteria to load, criterion provides note five.
• Linear relationships that keep the remaining resistors with values ​​that ten and five used to determine the grade they deserve, in the same linear relationship to the number ten and five.
DOCUMENTATION MODEL

Description: Semioctaedros association and tetrahedrons in two sheets, with additional node in the key and extra intake of cola at the nodes close to the bottom knot.
Failure: Loading as closely as possible to one side, put the right, would follow one of two sticks of going to the knot right bottom of the structure.
Bars = 164
Knots = 46

Hiperestaticidad = B + 6 – 3N = 32

Do you think this exercise is formative?