Torque effect
The torque effect experienced in helicopters and single propeller-powered aircraft is an example of Isaac Newton's third law of motion that "for every action there is an equal and opposite reaction."
In helicopters, the result of the torque effect is a tendency of the main rotor to want to turn the fuselage in the opposite direction from the rotor. A small tail rotor is the most common configuration to counter the torque effect.
In a single-propeller plane, the result of the torque effect is a tendency of the plane to want to turn upwards and left in response to the propeller wanting to turn (bank) the plane in the opposite direction of the propeller spin.