How Does a Ship's Compass Work?

ship-s-compass-work Credit: Kevin Cole/CC-BY-2.0

Gyroscopic compasses are used aboard transportation such as ships and airplanes. Spinning gyroscopes copy the behavior of a magnetic compass by using a magnetic compass as a reference. A motor keeps the gyroscope spinning, so it continues to point true north despite movement of the frame. A gyroscope adjusts itself quickly even in turbulence and rough seas.

By contrast, magnetic compasses must stay level to provide an accurate reading, and they tend to correct themselves slowly in reaction to the movement of the ship. Because of this tendency of magnetic compasses, most ships use gyroscopic compasses instead.

Gyroscopes seem to defy gravity through a phenomenon known as precession. Gyroscopes can resist motion acted upon its spin axis. If the spin axis is rotated, the gyroscope tries to spin at right angles opposite to the force acting upon the spin axis. When the top section of the gyroscope is moved to the side, it reacts by spinning 90 degrees to the left. The bottom half reacts by spinning 90 degrees to the right. The precession effect is in line with Newton's first law of motion, which states that a body in motion moves at a constant speed in a straight line unless acted upon by an unbalanced force.