3D Physics - Water Simulator (Difficulty: 2)

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Introduction

 

In this tutorial, you will learn to use the 3D physics engine to control many water drops (spheres) for a fun animation. The 3D physics engine will manage the movement of 3D objects for us, which allows us to easily create complex 3D simulations with only a few blocks of code.

 
 

Step 1 - Initialize 3D Scene with Physics Engine

 

Please create a new project, remove the dog sprite, and add these blocks to initialize the 3D scene, 3D axis and the 3D physics engine.

 
Note that the gravity is set to -600, which makes objects move down (negative Z direction).

 
 

Step 2 - Add a static ground

 

We will start with a large, flat box to serve as the ground. To make sure it will not move or fall, we just need to set its mass to 0.

 
 

Step 3 - Add a bucket using as a rectangular cube

 

Next, let’s add a bucket to hold the balls. The “rectangular tube” shape is very convenient for this purpose. It is essentially a box, but you can change the cap type to “bottom”, so it is open on top.

 
Notes:

• We need to move it up by 200 to be above the ground.
• You can apply any texture to it.
• We set its mass to be a large number like 10000, so it won’t be affected by the balls falling into it.
• Its restitution is 100%, so the balls will rebound when they hit the bottom or sides of this bucket.

 
 

Step 4 - Make the bucket spin

 

Since the bucket is controlled by the 3D physics engine, we can’t spin it using the “set speed” block. Instead, we need to use a special block in the “3D Physics” category to set the rotation speed around the Z axis:

 
 

Step 5 - Add a new sphere when SPACE key is pressed

 

To make the animation look cool, we will give each sphere a random color, which means their color/saturation/brightness are all random numbers. To keep the colors bright, we will set the range for brightness between 50 and 100.

 
 

Step 6 - Move the sphere to a random position

 

Next, we will move the new sphere to a random position, which means its x/y/z positions are all random.

 
 

Step 7 - Add a physics body

 

Lastly, we will hand over control of the ball to the 3D physics engine by attaching a “sphere” shape body to it. We will give it a very small mass so it won’t affect the movement of the bucket. Also, we will set it to 100% restitution, so it will bounce against other balls and the bucket.

 
 

Challenges

 

This project is very basic. You can challenge yourself with some of the following tasks:

• Add objects of different shapes and sizes
• Create a more complex container other than the bucket. For example, you can try to create a compound shape that is made of many boxes.
• Change the container to platforms: you can use many boxes to serve as platforms that are placed from top to bottom, so the balls will bounce from one platform to another like marbles.