newtons law...." every action has an equal and oppisite reaction..
P-Factor is an aerodynamic effect that causes propellor-driven planes to yaw when they are flown at high power and low speed (takeoff and climbout, for example.)
At low speeds, the plane flies at a substantial angle of attack, and so the airflow is not parallel to the plane's axis. Relative to the plane, the airflow is directed several degrees upwards. Now the prop axis is normally parallel to the plane's axis. As the prop rotates, on one side the blades are travelling upwards and on the other side they are travelling downwards. (On most planes, the prop turns to the right, as seen from behind,
The upwards angle of the airflow causes the downward (left) side of the prop to have a greater airspeed and angle of attack than the upward (right) side. So the downward (left) side of the prop generates more thrust. Pull harder on the right side of the plane than on the left and the plane will yaw to the left.

This is one of the reasons why most planes need a certain amount of left rudder to keep them straight during takeoff and climbout