My object falls through terrain.

Hi.

I am a particular unity and gamedev newbie overall. I have an object with Mesh Collider active. Whenever I add rigidbody to it, the object falls through terrain.

Please explain what I'm doing wrong.

Mesh Colliders are not useful on Rigidbodies unless they have Convex set, because otherwise they do not collide.

make sure that the bottom of your rigid body's collider is above the terrain at start, otherwise, if you have it "sitting" on the ground, the math might mistake it as already below the ground and start to fall. Simply lifting the object a bit so that the colliders don't overlap should do the trick

if your gameobject is exported from a 3d software make sure in the project view to tick the Generate Colliders and hit Apply.And then drag your gameobject in your scene.

i just encountered the same problem, its because my floor was a Plane, and when i try to change it with box, it doesn’t fall through… maybe yours too?
try to use “Box” instead of Plane.

does your terrain have a collidor on it as well?

i was having the same problem, but i fixed it by removing the terrain’s terrain collider and adding it back. not sure what that did, but it corrected something.

make sure the model wich gets trought terrain has a colider with attached physmaterial
if not you can make both

Make sure your box is on the ground ,the lower half of the box should not be below the ground .