In class our teacher shows a problem where he finds out the torque acting on a projectile at the highest point of its trajectory. He calculates the horizontal displacement from the vertical axis to the highest point as "r "and multiplies with "mg" as "F". Here I am a little confused. Isn't torque associated with rotational motion like "r" is the perpendicular distance from the rotational axis ? How we can treat a projectile motion as a rotatinal motion ?