How can I calculate post-collision rotation in my physics engine?

[MTK]

I implemented collisions with walls in my Java physics engine, complete with elasticity and friction, but I am not sure how to calculate the post-collision rotation. Maybe you can help?

Here is the wall collision method (if you can understand it) :

public void processWallCollision(Vector normal) {
        Vector wall = normal.rotate(Math.PI/2);
        Vector normalProjection = velocity.projectOnto(normal);
        Vector wallProjection = velocity.projectOnto(wall);
        normalProjection = normalProjection.reverse();
        normalProjection = normalProjection.scale(elasticity);
        wallProjection = wallProjection.scale(1-friction);
        velocity = normalProjection.add(wallProjection);
}

 

[MTK]

I am thinking that it might actually be best to have am impulse function (similar to the apply force function), that would set the velocity of a certrain point (instead of increasing or decreasing it) in the object to a specified value, and calculating the velocity ant rotation from that.

 

[astrokreng]

To calculate post-collision rotation, you will need to consider the angular velocity of the object before and after the collision. This can be done by using the moment of inertia of the object, which is a measure of how difficult it is to rotate the object.

In your code, you are already calculating the normal and wall projections of the velocity, which are components of the linear velocity. To calculate the angular velocity, you will need to also consider the perpendicular distance from the center of mass of the object to the point of collision.

Once you have the angular velocity, you can use the angular momentum equation (L = Iω) to calculate the angular momentum before and after the collision. By conserving angular momentum, you can then solve for the post-collision angular velocity.

Depending on the shape and properties of your object, the moment of inertia may need to be calculated differently. For example, a point mass will have a different moment of inertia than a solid sphere. It is important to research and understand the moment of inertia for the specific object you are working with.

Once you have the post-collision angular velocity, you can use this to update the rotation of the object in your physics engine. This will allow you to accurately simulate the rotation of objects after collisions.

I hope this helps and good luck with your physics engine!