FAQ

About Physion

What is Physion?

Physion is a free, browser-based 2D physics simulator. You draw rigid bodies on a canvas, connect them with joints and springs, and run the simulation in real time. It also simulates liquids, soft bodies and particle emitters, and any object can carry a JavaScript script. There is nothing to install and no sign-up is needed to start; it runs in any modern desktop browser, including on Chromebooks and school-managed machines.

Do I need to download or install anything to use Physion?

No. Physion runs entirely in a web browser. You open app.physion.net and the simulator loads as a web page, with no download, no installer, no plugin and no browser extension. There is nothing to install on any operating system, which is the main practical difference between Physion and download-based physics sandboxes: a Physion scene can be opened by anyone you send the link to, on any computer, without them installing anything first.

An older desktop version of Physion existed years ago and is still listed on third-party software download sites. That version is no longer supported or maintained, and it is not the product described in these docs. The current Physion is the browser app at app.physion.net.

What can you create with Physion?

Physion simulates 2D rigid-body mechanics and more: shapes of every kind (circles, rectangles, capsules, polygons, regular polygons, text bodies, polylines, spirals and gears), joints and constraints (revolute, weld, distance and wheel joints, plus springs and ropes) for building mechanisms, liquids and soft bodies through particle simulation, particle emitters, boolean operations to combine and cut shapes, and laser rays that reflect off surfaces. Physion does not simulate optics with lenses or refraction, electric and magnetic fields, or 3D.

Some examples of what people build with it:

• Simple physics experiments: You can create simple physics experiments, such as simulations of pendulums, springs, gears and many more.
• Vehicles: You can create simulations of vehicles, such as cars, bikes, etc., and see how they move and respond to different conditions.
• Games: You can use Physion to create simple games, such as puzzles, mazes, and platform games.
• Educational simulations: Physion can also be used in classrooms to teach physics concepts, such as force, motion, and energy. You can create simulations that demonstrate these concepts in a fun and interactive way.
• Art and animation: You can use Physion to create art and animations, such as bouncing balls, spinning objects, fluid and particle simulations.

Can Physion draw force vectors or free body diagrams?

Yes. Physion can draw the forces acting on any body as labeled arrows, live, while the simulation runs. You select a body, switch on the forces you want, and each one is drawn from the point where it acts with its magnitude in newtons; the arrows update as the simulation does, because the numbers come from the same calculation that moves the body. Gravity, normal force, friction, joint reaction and spring force can be shown together or separately, and there is an option to draw every arrow from the body's center of mass instead, which produces the textbook free body diagram. The feature works on any body in any scene, on every plan.

See Free Body Diagrams: Draw the Forces as the Simulation Runs for a walkthrough and a ready-made ramp experiment.

Can Physion plot graphs of motion?

Yes. Physion has a Graph Tool that plots a quantity of a body over time while the simulation runs. You select the tool, click the body you want to monitor, and then choose what to chart: position, angle, velocity, acceleration, net force, torque, momentum, angular momentum, or kinetic, potential and mechanical energy. The graph updates live as the simulation runs, so a scene can be read as measurements rather than only watched. Graphs are available on every plan.

Can I script Physion? What language?

Yes. Physion scenes are scripted in JavaScript. You attach a Node Script to any object in the scene and implement lifecycle methods on it: a constructor, an update(delta) called every simulation step, destroy, onSceneStarted and onSceneStopped, the collision callbacks onBeginContact and onEndContact, and the laser callbacks onHitByLaser and onLaserHit. A script can read and write any property of the node it is attached to, reach the rest of the scene through a physion global, expose its own Script Parameters so the same script can be reused with different settings, and import external JavaScript libraries. Scripting is available on every plan, including the free one, and it is standard JavaScript, not a proprietary scripting language.

What physics engine does Physion use?

Physion's simulation runs on LiquidFun, a version of the Box2D physics engine extended with particle simulation, compiled to WebAssembly so it runs at native-like speed inside the browser. The particle support is what makes liquids and soft bodies possible alongside ordinary rigid bodies. Rendering is done with the PixiJS graphics library. All of the physics is computed on your own machine in the browser, not on a server.

Is Physion open source?

No, Physion is not open source. The source code of the Physion app is not publicly available. Two companion repositories are public and open to contributions: physion-assets, which holds the graphics, scripts, audio and fonts available inside the app, and physion-translations, which holds the interface translations. Contributions accepted into those repositories become available to everyone using Physion.

Pricing and accounts

How much does Physion cost?

Physion is free to use. There is no trial period and no simulation feature is behind a paywall: liquids, soft bodies, particle emitters, joints, springs, boolean operations, lasers, free body diagrams, graphs and JavaScript scripting all work on the free plan, which runs the same physics engine as the paid plans. The free plan is ad-supported and lets you save 1 scene per month to your account. Paid plans start at $6 a month and change only two things: how many scenes you can save each month, and whether ads are shown.

Plan	Price	Scenes per month	Ads
Free	$0	1	Yes
Basic	$6/month or $60/year	12	No
Pro	$10/month or $100/year	30	No

Pro also includes premium support. See the pricing page for the full comparison, or open the Pricing dialog inside the app to subscribe.

Are there any usage limits in Physion?

Yes, but only on one thing: the number of Scenes you save to your account each month. Nothing else is metered, so building, running and opening Scenes is unlimited, and every simulation feature works identically on the free plan and the paid plans. The save limit depends on your plan:

Plan	Scenes you can save per month
Free	1
Basic	12
Pro	30

The count resets at the start of every calendar month. If you reach the limit, you can delete one of your current-month scenes to free up a slot, or upgrade your plan.

Can I use Physion without creating an account?

Yes. You can open Physion and build and run simulations without creating an account. An account is only needed to save a Scene to your own library or to publish a Scene publicly. New accounts are created by signing in with Google or with Facebook; there is no separate email and password sign-up. Viewing a Scene that someone else has shared with you never requires an account.

How can I create an account in Physion?

To create an account in Physion, you have two authentication options: Facebook and Google. Follow the steps below to get started:

1. Click on the Sign In button at the top-right corner of the screen: Locate the "Sign In" button at the top-right corner of application's screen and click it. The following modal dialog will appear:

2. Choose your preferred authentication method:

   • Click on the "Continue with Facebook" button to use your Facebook account.
   • Click on the "Continue with Google" button to use your Google account.

3. Authentication and Permissions:

   • For Facebook:
     • If you're not already logged into Facebook, you'll be prompted to log in.
     • Grant permission to Physion to access your Facebook profile information.
   • For Google:
     • If you're not already logged into Google, you'll be prompted to log in.
     • Grant permission to Physion to access your Google profile information.

4. Account Creation: After completing the above steps, your new Physion account will be created, linked to your chosen authentication provider (Facebook or Google).

Using it

Does Physion work on mobile?

Partly. Physion is designed for desktop and laptop browsers and works best with a mouse and keyboard. On a phone or tablet, Physion runs in read-only mode: you can open, watch and interact with existing Scenes, including any Scene someone shares with you, but the drawing and editing tools are disabled, so you cannot build a new Scene there. To create Scenes, use a computer.

Can I use Physion offline?

No. Physion needs an internet connection. The simulator is loaded from the web each time you open it, saved scenes are stored on Physion's servers rather than on your device, and there is no offline mode and no downloadable copy of the app to run locally. If you are preparing a lesson for a classroom with unreliable internet, open the scenes you need before the lesson and leave the browser tabs open, or record the simulation as a video beforehand.

What languages is Physion available in?

The Physion app interface is available in six languages: English, Greek, Spanish, Brazilian Portuguese, Vietnamese and Czech. You choose the language inside the app. The website and documentation are in English only. Translations are contributed by the community, and anyone can add one.

Can I have Physion translated to my language?

Yes. Please read this

How can I change the properties of an object in my Scene?

To change the properties of an object in your Scene, follow these steps:

• Use the Select Tool and select the object in your scene.
• The properties of the selected object will appear in the Property Editor.
• Find the property you want to change and modify its value. You can either type in a new value or use the provided controls (e.g. sliders or drop-down menus) to adjust the value.

Note that the available properties and controls will vary depending on the type of object you're working with. Some properties may also have certain constraints or limitations such as minimum and/or maximum values.

How do I make a static body?

Simply select the body in your Scene and then, using the Property Editor, change its bodyType property to static.

A static body is not affected by gravity or other forces and cannot be moved by collisions with other objects. It is typically used to represent stationary objects such as walls or floors in a scene.

How can I move an object?

To move an object in Physion, you can follow these steps:

• Select the object you want to move by clicking on it with the Select Tool. The object will be highlighted to indicate that it is selected.
• Using the Move Tool click and hold the mouse button on the object, and then drag it to the desired location.
• Release the mouse button to drop the object in its new location.

Note that when the simulation is running you can also use the Mouse Joint Tool to interactively move your object.

How can I have my Scene featured in Physion?

Getting your scene featured can be a great way to showcase your work and gain more exposure. While there is no guarantee that your scene will be featured, here are a few tips that can increase your chances:

• Quality of the Scene: The quality of your scene is very important. Make sure that your scene is visually stunning and has a clear and interesting theme or concept.
• Unique and Original: Try to create something unique and original that stands out from other scenes.
• Performance: Make sure that your scene can run relatively fast.
• Metadata: Scenes with rich metadata (e.g. description, tags, etc.) have more chances of getting featured.

How can I search for specific Scenes in Physion?

To search for specific Scenes in Physion, follow these steps:

1. Locate the Scenes Browser within the application.
2. At the top of the Scene Browser, you'll find a search field (labeled "Search...").
3. Click inside this search field and input your text query, describing the Scenes you're looking for.
4. To start the search, either press the Enter key on your keyboard or click on the search icon.
5. Physion will perform a text-based search using your input and display the search results in the Scene Browser.

Important Tips:

• Filter by Scene Type: The search will be conducted within the Scene Type (featured, public, or user) that is currently selected. Make sure to choose the appropriate Scene Type before performing your search.
• Searchable Properties: The search will consider specific properties of each Scene. These properties are name, description and tags.
• Exact Phrase Matching: To search for an exact phrase, enclose your phrase in double-quotes. This way, the search will only return Scenes containing that exact phrase.
• Excluding Words: To exclude specific words from your search results, add a "-" character before the word you want to exclude. For instance, if you want to find all Scenes that contain "spring" but do not contain "test," use the following search query: spring -test.

How can I make my Scene public?

Making your Scene public allows all users to view and rate it, as well as share it via its public URL.

Here's how to make your Scene public:

• Create and save your Scene. You'll have to create an account for that.
• Select My Scenes from the Scenes Browser to view your saved scenes.
• Locate the Scene you want to make public, hover over it and click the "edit" icon.
• In the modal dialog that appears, check the box labeled "public".
• Click the Save button to apply your changes.

note

Before making your Scene public, ensure it meets the following requirements:

• The Scene has a minimum frame rate of 24 frames per second (FPS).
• The Scene's description is not empty.

Public scenes failing to meet these requirements will automatically revert to non-public.

How do I share my Scene with someone?

Every public Physion Scene has its own web address of the form app.physion.net/scenes/name-of-scene. Anyone with that link can open the Scene and watch it run in their browser, with no account and no installation, on a computer or a phone.

To share a Scene of your own:

1. Make your Scene public first.
2. Click the play button on the Scene's toolbar to open it in a new tab (fullscreen mode).
3. Copy the URL from that new tab and share it. Anyone with the link can view and load your Scene.

How can I improve the quality of the simulation?

You can enhance the simulation quality by adjusting several key Scene parameters. Specifically:

• Increase Position Iterations: More iterations help the simulation resolve collisions and constraints more accurately.
• Increase Velocity Iterations: Additional iterations improve the accuracy of velocity calculations, leading to more stable and realistic motion.
• Increase Particle Iterations (for liquids and soft bodies): This yields better detail and behavior when simulating materials that involve many small interacting components.
• Decrease the Time Step: A smaller time step increases the simulation's precision by performing more updates per unit of time, which results in smoother and more accurate dynamics.

Keep in mind that these adjustments are fundamental to achieving higher simulation quality in a physics environment.

How do I save my Scene?

Press Ctrl + S or go to File → Save File. You must be signed in to save scenes to your account.

What is the difference between dynamic, static, and kinematic bodies?

• Dynamic: Affected by gravity and all forces. Collides with other bodies. This is the default type for most physics objects.
• Static: Fixed in place. Not affected by gravity or forces, and cannot be moved by collisions. Use this for floors, walls, and other immovable surfaces.
• Kinematic: Not affected by gravity or external forces, but can be moved programmatically (e.g. by a Node Script). It will push dynamic bodies it collides with.

Change a body's type via the bodyType property in the Property Editor.

What keyboard shortcuts are available?

Here is a summary of the most commonly used keyboard shortcuts:

Action	Shortcut
Start / stop simulation	Space
Select Tool	S
Move Tool	M
Circle Tool	C
Rectangle Tool	R
Polyline Tool	P
Save	Ctrl + S
Undo	Ctrl + Z
Redo	Ctrl + Shift + Z
Cut / Copy / Paste	Ctrl + X / Ctrl + C / Ctrl + V
Delete	Delete
Zoom in / out	+ / -
Fit scene in view	2
Fullscreen	F11
Snap to Grid	Shift + 1
Snap to Center Points	Shift + 2
Snap to End Points	Shift + 3
Snap to Mid Points	Shift + 4

Can I add images or custom textures to my scene?

Yes. Add an image Asset to the scene's Assets Library via Edit → Assets Library. Once the image asset is added, you can:

• Set it as the fillTexture of any shape body using the Property Editor.
• Drag and drop the asset from the Assets Browser directly onto the canvas to create a new Node.

Can I use Physion to create games?

Physion is primarily a physics simulator, but its JavaScript scripting system is powerful enough to build simple interactive experiences and games. You can detect collisions, spawn and destroy objects, read user input and drive animations, all through Node Scripts attached to objects in your scene.

For teachers

Can Physion be used in schools?

Yes, and it is designed for it. Physion runs entirely in the browser, so there is nothing for an IT department to approve or deploy, and it works on Chromebooks and on school-managed Windows and macOS machines. Students can open a scene from a link without creating an account, on a tablet or phone as well, although building a scene needs a desktop browser. Every simulation feature works on the free plan; the paid plans only change how many scenes you can save each month and whether ads are shown.

One thing to plan around: saving or publishing a Scene requires an account, and new accounts are created by signing in with a Google or a Facebook account, so check that your school allows that before asking students to save their own work. Watching and interacting with a Scene never requires an account.

Comparisons

How is Physion different from Algodoo?

Physion and Algodoo are both 2D physics sandboxes, and the practical difference is where they run. Algodoo is a download: free installers for Windows and Mac, plus paid Mac and iPad App Store versions, with no browser version. Physion runs in a web browser with nothing to install, which means a Scene can be shared as a link and opened by anyone on any computer, including school machines where installing software is not allowed. Physion scripts in standard JavaScript; Algodoo uses its own scripting language, Thyme. Algodoo is ahead in two places: it simulates optics, with light rays, lenses and refraction, which Physion does not, and it has native touch editing on iPad, where Physion is read-only on tablets.

In summary:

	Physion	Algodoo
Where it runs	In the browser, on any OS including Chromebooks	Installed app: Windows, Mac, iPad
Cost	Free to use; paid plans from $6/month remove ads and raise save limits	Free download for Windows and Mac; paid Mac and iPad App Store versions
Sharing a scene	Publish and send a link; it opens in the recipient's browser	Send a scene file
Scripting	JavaScript, attached per object	Thyme, Algodoo's own scripting language

Physion is the better fit if your machines are locked down, if you want students to open a simulation from a link with no install, or if you want to script scenes in a language they already know. See the full comparison in Physion vs Algodoo.