Join Thanassis Pozantzis for an in-depth discussion in this video Bounce, part of Dynamics in CINEMA 4D.
One of the values that defines the interaction between two dynamic objects is the bounce value. Let me show you what I mean. For this example I will create a cube, not a floor, and I will bring it down by approximately 100 so that at the top of the cube, which is 200 in height, is where our floor used to be. Just for clarity, nothing else. Let me move the cube on this side. I'm going to create another cube, and move it on the other side. I'll call one cube, cube soft, and the other cube, cube hard.
The same way, I'm going to create two spheres. Make my sphere a bit smaller. Bring it on this side, place it over the cube. Make a copy. Drag it over here. Select both spheres, lift them up. And adjust my camera view. I'll change my displacing text as well, for clarity's sake. So now we have two spheres falling on the tops of two cubes. I'll select all the objects, right click, and add simulation tags. And don't forget, select the two cube simulation tags and tell the object to become static so that they won't fall down.
I'll rewind, press play, and pretty much you see the spheres falling identically. Now, in real life, objects bounce differently depending on the hardness of the surface they hit. At the same time, they bounce differently depending on how hard they are. Now hardness and weight, or mass, has no correlation. So we can take a very hard ball made of glass, and get a very heavy ball made of lead.
Lead is softer than glass, but is heavier than glass. The glass will jump higher when it bounces on the floor. Provided it doesn't break, but you understand what I mean. So, this parameter is inside the tag. If you check any of the rigid body tags, you will see that in the collision tab, down here, it says bounce. By default, bounce is set to 50%. This is not a literal value.
It's close. It doesn't mean it's 50% of the perfect hard object. In theory, if all our objects in the scene had bounce values of 100, then we wouldn't lose any kinetic energy when the object was bouncing. So you'd have two spheres jumping up and down forever. But even if I do set all the bounce values to 100, that won't happen because we have different errors.
Now you can see the balls are going higher, and if I add a few more frames, you will see them going higher and higher. But don't let that phase you. All you need to remember is that, in theory, when bounce values are close to 100, then every bounce does not lose any energy as happens in real life. And this is what happens with very hard objects. The harder an object is, the less of its kinetic energy it loses when it bounces.
Whereas if these were zero, then would have a plastic bounce. But even this, as you can see, there is a small bounce where there shouldn't. And again, this is the mathematical error. You just saw me change the values for all the objects. Why do that? Let's assume that our two spheres had a bounce value of, let's say 85. Because they're quite hard. Now, the soft cube has a value of five.
And the hard cube has a value of a 90. If I wind and play. You will see that the soft cube will, let's say, absorb more of the bounce, so it will bounce less times. Whereas the hard one won't, and it will allow the marble to bounce more times. When you have different numbers between the colliding objects, which is exactly what you will have, then the bounce value is approximately, and this is just a rule of thumb, the average of these two.
So if you add 85 and 5 equals 90, divided by 2. Equals 45, it'll be close to if both these objects had a bounce value of 45. Because this happens in real life. If you had a hard floor and threw on it, let's say, a table tennis ball, even though it's light, it doesn't mean it's not hard. Or a golf ball.
You will see that the golf ball will bounce many times. If you have a floor with a carpet, which makes it very soft, no matter how hard the object you're throwing at the floor is, it will not bounce. So, at the same time, if you have the hardest possible floor, and you drop a ball made of play doh, play doh does not have any elasticity, then it won't bounce. So you understand that a bounce parameter is a parameter that affects both the interacting objects.
This course was created by Thanassis Pozantzis. We're honored to host this training in our library.
- Making objects fall with gravity
- Creating dynamic hierarchies
- Controlling the collision shape
- Adjusting properties like Bounce and Density
- Adding keyframed elements to a simulation
- Adjusting the dynamic simulation