In electromagnetics, the catapult effect is a phenomenon occurring when a current is passed through two wires connected by a loose wire in a magnetic field

Magnetic field

A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

. The loose wire is then catapult

Catapult

A catapult is a device used to throw or hurl a projectile a great distance without the aid of explosive devices—particularly various types of ancient and medieval siege engines. Although the catapult has been used since ancient times, it has proven to be one of the most effective mechanisms during...

ed horizontally away from the magnetic field. This occurs due to the magnetic forces acting in the wires and in the magnetic field itself.

Implications of the catapult effect on science

The idea of the catapult effect is central in our day to day lives as it greatly contributes to our understanding of the electric motor (which we use in numerous appliances from washing machines to vacuum cleaners and cars). The catapult effect helps to explain the movement of the motor itself and is thus used widely in science.

The left hand rule

The left-hand rule helps to explain why the loose wire moves as it does in the catapult effect. The left hand rule naturally takes its name from the left hand anemyl the thumb and the next two fingers. If you arrange the fingers in a three dimensional shape so the first finger and thumb are perpendicular to one another and the second finger is perpendicular to the first aiming downwards then this is the way magnetic fields with addition of flowing current will act. The thumb represents the direction of motion. The first finger represents the direction of the magnetic field while the second finger represents the direction of the current. Therefore as long as you know the direction of one of these three variables you will be able to predict the other two using the left hand rule. This is used in electric motors.