Posted by: T. Boyd | February 10, 2010

The Strange Catapult Force

“It is the glory of God to conceal a matter;  to search out a matter is the glory of kings” (Proverbs 25:2)

In the early days of science,  it was believed that there was no connection between electricity and magnetism.  The magnetic force was found in rocks with iron ore in them, and then magnets were made by rubbing these special rocks against iron or steel.  These were then used to make magnetic compasses, giving a wonderful advancement in navigation.

The early experiments with electricity included the investigation of lightning, made most famous with Benjamin Franklin’s dangerous flying of a kite during a thunderstorm (he and his assistant could have been easily killed by a direct hit).   It was also discovered that heat and light could be produced by passing the current from a battery through a thin wire.

However, to show there was no connection between electricity and magnetism, a magnetic compass was placed beneath a wire through which electric current was passed. The equipment was arranged so that the wire was at right angles to the compass needle, thinking that surely if there were a force between them, the needle would be deflected to become parallel to the wire.  But there was no deflection.

However, in 1820, Hans Oersted at the University of Copenhagen while preparing this demonstration, discovered that if the compass needle and the wire are parallel to start with, that the needle would swing to being perpendicular to the wire – just the opposite of that which had been predicted.  It was a serendipitous moment.  He had shown a connection between electricity and magnetism.

This led to the building of an electric catapult, hence the nickname given this force, which today is called the Lorentz Force, named after Hendrik Lorentz who formulated the mathematical equation in 1892 that describes it.

To picture the catapult, imagine a child’s swing scaled down to fit on top of a table.  You would use thin wires instead of chains to hold up the “seat” which is also made of wire. Everything would be connected to a battery so that electric current will flow down one “chain”, through the “seat”, and back up the other “chain.”

Directly below the “seat” you would hold a bar magnet with the north pole pointing upward. When the current was turned on through the “swing,”  the “seat” would be “catapulted” forward or backward, depending on the direction of the current.

You may have seen toys that swing back and forth tirelessly, run by a single AA battery that is based on this principle.  In fact the electrically powered baby swings operate by this catapult force. More importantly this Lorentz Force is what powers electric motors which have played such a large role in the twentieth and twenty-first centuries.

Proverbs says, “It is the glory of God to conceal a matter;  to search out a matter is the glory of kings” (Proverbs 25:2)  It is such a blessing that He also puts in our hearts and minds the desire to discover these hidden laws of His creation.


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