• ## Physics in play

Classical mechanics (free fall)

## The story in two words

The students embody a group of engineers in support of operations carried out in the field. They discover that they must assist a secret agent who has recovered North Korean leader Kim Jong Un’s smartphone.

## Preparations

You need a place where students can work in groups, and craft together. Ideally, a place that is unknown to them, so as to get them out of their habits. A TD room may be suitable, if it is not too full of tables (and if the tables are installed in an island). You also need a place for the ultimate test, with a height difference of about 5m: window, footbridge. Obvious safety conditions must be taken when throwing objects out the window. For hardware, see below.

## INTRODUCTION

Show Video KJU I6: A spy in North Korea explains the situation to them – he got Kim Jung Un’s smartphone, he’s going to send them from a wall. There is a security camera. It indicates that the GH12 protocol must be followed (the spy mistakenly talks about the GH13 protocol instead, so French).

optional: The supervisor gives them a way to communicate with the spy (ex: via minnit.chat or a whatsapp channel or a discord that the supervisor will use in secret to play the spy). Then let the participants possibly ask questions to clarify the mission.

The test consists of making a protection to be able to drop a fragile object from above by following the GH12 protocol. Frugal materials are provided, and students work in groups.

Choose from 2 versions of the GH12 protocol to give to students:
– a simple version, the only instruction is that the egg resists the fall.
– a more advanced version, which requires students to do a video analysis of the fall to assess the frictional forces of the air.

– the camera must be able to film the fall, which forces the students to slow down the fall (set a minimum duration)
– once the device is on the ground, you have to be sure that the camera has a precise orientation (to film in the right direction).

This activity can be more or less advanced depending on the constraints you impose:
– tracking of the fall by video analysis (use the Fizziq application for example)
– impose a minimum time and orientation constraint during the fall in order to film it.

Typical process :

Device manufacturing time: 1h30 – The students design a device in groups, test it, improve it.

Final test: 20 to 30 mn : all the groups, one after the other (or all at the same time if time is short), test their device in real size (drop it from a height of about 5 m) and check whether the conditions emitted by the protocol are verified. For this test, the smartphone is replaced by an egg: the egg must be intact at the end of the fall. All the students must then agree on the device to be sent to the astronauts (take a photo of the plan and the device that is sent to the spacecraft).

Optional: if we want to avoid having to choose between the different devices (to avoid competitive tensions), we send the plans of all the devices to the astronauts as well as their test results, and we say that they will be the ones who will choose according to their constraints local (equipment, space suits, etc.)

If you have many students: groups of 3/4 students work well. If the groups are larger, we can provide tutorial writer functions: some students take charge of writing instructions for making the device. We can insist on the important nature of this document and its duty of clarity. Otherwise, photos are enough to communicate with the astronauts. If the groups are larger, plan a trajectory analysis activity that is supported by a few students

Equipment: The C2309 kit

These are what the spy has. It can be modified according to your stocks. This is small DIY material, the list offered (in pdf and pptx format) has been tested and works but can be changed easily. Ideally, each group should have a C2309 kit at their disposal, but in practice the easiest way is to make the equipment available in the room. The quantities available are then greater than what is indicated in the kit (you can have 100 straws, even if the kit indicates that the spy only has 10): the groups must be careful not to exceed the quantities in their device (but several groups can use 10 straws).

DIY equipment: in addition to the kit, provide cutters, scissors, glue guns, pliers, protective and cleaning equipment: cutting mat, plastic sheeting, garbage bags, brooms… Eggs must also be provided for the final test.

## EPILOGUE

They receive a message indicating that a video from the spy services will arrive after a certain time (good time for a short break or tidying up):

final video KJU E6: an agent in South Korea tells them that the services have recovered the smartphone – it allowed them to access the codes of the last missiles then end credits (you can add the names of the participants, students and teachers to the credits).