I want to apply a force perpendicular to the velocity of the object. (I’m simulating a magnetic field exerting a force on a charge).

My code looks like this:

```
function FixedUpdate () {
this.rigidbody.AddForce(Vector3.Cross(this.rigidbody.velocity, bField));
}
```

The cross product makes sure the force is perpendicular to the velocity and the bField. I set bField in the Z direction and initial velocity were in the Y direction. *If it were working optimally*, the direction of the velocity would change but the magnitude of the velocity would stay constant, the object would move in a circle of constant radius in the XY plane. However the object is speeding up, meaning that the force is not exactly perpendicular (even though the Vector3.Cross gives a perpendicular force vector).

Any thoughts on how I can keep the Magnitude of the Velocity constant?

thanks