# Bounciness in Rigid Body

I tried to make up a rigid body simulation (a torus falling onto a plane) and I have tried to modify the bounciness from 0 up to 400, but I didn't observe any difference. What this parameter is supposed to do and how do I recognize the effect of the parameter ?

## 1 Answer

The setting controls how much energy the surface removes from a collision. The parameter can vary between 0.0 and 1.0 (you shouldn't set it outside that range) and a setting of 0.0 indicates no bounciness (all energy is removed). Increasing it up to 1.0 allows energy to remain after the collision.

Note that the collision energy is affected by both objects taking part in the collision so if either of the objects is set to 0.0 then no energy remains and there will be no 'bounce'. The Bounciness from both objects can be multiplied together to give a value of bounciness resulting in those objects colliding.

For example, for two objects each with a bounciness of 1.0, the result of a collision will have 1.0 x 1.0 = 1.0 (ie, all) of the energy before the collision. If either is zero then the result will be zero energy of their initial motion after the collision. For in-between values, the same holds - eg, if both have Bounciness of 0.8 then 0.8 x 0.8 = 0.64 of the energy will remain after the collision - ie, a ball would bounce 64% of the way back up from its starting height if it fell onto the surface.

In your case you likely have the other surface set to its default value of 0.0, resulting in no bounce (since anything multiplied by 0.0 is 0.0).

• Oh, I can see the point now: I have to set the other object bounciness also different from zero, right ? What did you mean by your **As an example, ** ? – user3357120 Nov 11 '20 at 17:34
• That's exactly it. Sorry about the 'As an example' text - left behind after editting. I've fixed it now. – Rich Sedman Nov 11 '20 at 17:36
• if both are 0.8 the result will be 0.64 only if hited directly straight onto the plane, i.e. not rotated ? – user3357120 Nov 11 '20 at 17:45
• Yes - if a ‘straight-on’ collision (the collider is travelling along the surface normal). If a more glancing blow then obviously the ‘bounce’ will be affected (I presume it would be scaled based on the cosine of the angle with the normal... if my understanding of the physics is correct). – Rich Sedman Nov 11 '20 at 17:48