public void ReleaseProjectile()
{
if (projectileInstance)
{
projectileInstance.GetComponent <Rigidbody2D>().isKinematic = false;
projectileInstance.GetComponent <Rigidbody2D>().AddForce(arc.direction * Arc.CalcLaunchSpeed(arc.range, transform.position.y + 5.0f, Physics2D.gravity.magnitude, 0), ForceMode2D.Impulse);
}
}