# Physics (activity)

 This activity is now hosted at the Sugar Activity Library. The information here is likely to be out-of-date. Consult the new pages for "Physics (activity)" first:
Physics
 .xo Bundle – Physics-0.2.xo

# Physics

Physics is a physical world simulator and playground -- you can add squares, circles, triangles, or draw your own shapes, and see them come to life with forces (think gravity, Newton!), friction (scrrrrape), and inertia (ahh, slow down!).

We also plan to add forces such as: magnetism, springs, and motors

## Get Physics!

Click this link in browse: Physics-0.2.xo OR (for the development version...) Open up the Terminal activity and follow these steps:

```sudo yum install git
cd ~/Activities/
git clone git://dev.laptop.org/activities/physics
mv physics Physics.activity
# Then press ctrl + alt + erase to restart sugar.
# The newest version of physics is installed! (but may not be stable!)
```

# Usage

## Drawing objects

• Boxes - Rectangles of any dimension
• Use: click (top-left corner) drag + release (bottom left corner) -- like dragging a selection box in a photo editor
• Circles - Circles of any radius
• click (center) drag + release (outer edge)
• Triangles - Triangles (equilateral) of any size and initial rotation
• Use: click (center of base) drag + release (tip)
• Polygons - As many sides as you would like. Draw your own N-gon.
• Use: Click for each point, to end: right click, or left click in the circle around the original point
• Magic Pen
• Use: Click and hold to draw any shape you'd like!

## Using tools

• Grab - Drag existing objects around with the mouse
• Connect
• Click on any object, drag to another object + release to create a distance joint
• Click on any object to add a revolute joint (like a push pin!)
• Destroy - Click on an object to destroy it, or draw a line of destruction--destroying everything in its path!

## Class Challenges

### Egyptian Pyramid

How did the Egyptians build the pyramids using just human effort? They didn't have cranes, trucks or even cars. Make a block with a high mass and use a weak grab tool. How can you get it across the screen?

### Vertical Tennis

Can you use motors to make a device that hits a ball up and down?

### Lotus

Reproduce the Lotus effect in the classroom.

# Plan to Add / Requests

These are the features we would like to add, and if you think you can help us out please do! (currently being placed into Trac)

1. There are some tools that need to be added
• Need to implement gears, prismatic and revolute joints in elements (already implemented in Box2D)
2. Need a way to change the properties of an object (density, rotation, strength (for breaking), bounciness, friction, color - ticket #7592
3. More physics!
• Magnetism
• Springs -- via prismatic joints?
• Breakable bodies
• Note: We are using a rigid body simulator (box2D). All of the above need to be implemented using forces on rigid bodies. Breakable bodies can be achieved a few different ways:
1. When a body 'breaks' it is removed from the physics engine and some kind of graphical animation indicates that it has been broken and dissipated
2. When a body 'breaks' it is removed from the physics engine and is replaced by some new (smaller, fragment-like) rigid bodies (kind of like an explosion)
3. When a body 'breaks' it is removed from the physics engine, it's shape is calculated and then split into smaller polygons which are then added as rigid bodies
4. Save / Exporting scene - ticket #7585
• Standard format interoperating with a browser-based playground
5. Objectives and constraints
• Incredible machine style objectives (get the ball into the basket, knock the triangle off the screen, etc)
• You only have 4 boxes, 1 meter of magic pen, and one triangle, etc.
6. Sonification - ticket #7593
7. Joystick button and Physics for game-making

# Ideas to try

• Sorting different sized balls in to two buckets, large and small (with no jams).
• A cyclic mechanism for lifting balls from the bottom of the screen to the top, again and again.
• Try dropping 2 different mass objects at the same time.
• Experiment with pendulums of different lengths and masses.
• Try building a mechanical binary clock.
• Convert rotation into parallel motion using pistons.
• Experiment with touching one motorised circle against one pinned circle of various sizes.
• Try building a rag-doll puppet and make it dance in a convincing way.
• Use just links and circles to make a structurally sound Eiffel Tower.
• Try building a ratchet
• Try building an analogue clock face where the min hand goes around 60 times for each hour.

Activity Summary

 Icon: Image:Activity-physics.svg Genre: Math and Science Activity group: Short description: A physics playground for the XO. Description: A physical world simulator and playground -- you can add squares, circles, triangles, or draw your own shapes, and see them come to life with forces (think gravity, Newton!), friction (scrrrrape), and inertia (ahh, slow down!). Maintainers: User:Alexlevenson, User:Bjordan Repository URL: http://dev.laptop.org/git?p=activities/physics Available languages: English Available languages (codes): en Pootle URL: Related projects: x2o Contributors: User:ewjordan URL from which to download the latest .xo bundle http://dev.laptop.org/~bjordan/Physics-0.2.xo Last tested version number: 0.2 The releases with which this version of the activity has been tested. 7.1.2 (656), 8.1.0 (703), 8.1.1 (708) Development status: 3. Alpha Ready for testing (development has progressed to the point where testers should try it out): smoke tested : test plan available : test plan executed : developer response to testing :