Potholes to roll the ball

Hello everyone, I'm making a Roll a Ball game, the problem is that the sphere gives boats, as if there were small. potholes. Move the sphere with the AddForce (0,0,20, Force Mode.Force) function. Moving at low speed the Y axis varies little. Moving at high speed are jumps. Both the ball (sphere) as the path (cube) are those of Unity. I also tested with ConstantForce and velocity, but still. I have not the slightest idea that it can be If anyone knows it could be me would be helpful, thanks.