Lesson Summary We use magnets in many ways, but at one time, their only use was in compasses to guide explorers in unknown seas and territories.  In this lesson, students investigate the behavior of a magnetic compass and learn about its place – and importance – in human history.  They then build and adjust their own working compass and begin to explore its characteristics. Teacher Background The earth acts as one big magnet.  That is why the magnets in compasses (compass needles) align the way they do.  Compass needles point toward the earth’s magnetic poles, which are close to the geographic poles. No one knows for certain what causes the Earth’s magnetic field.  It is still a mystery.  Evidence from old rocks indicates that the Earth’s magnetism (magnetic field) had moved around a bit, and even reversed itself repeatedly in the past. Magnets always have at least two “poles” – two places where the magnetic force is strongest.  We label the end of the magnet the “north-seeking pole” if it points to the earth’s geographical north pole; we call the other end of the magnet the “south-seeking pole.”  Learning that “opposites attract” often creates a logic problem for students.  This means that north and south poles attract.  The north pole of a magnet points toward the geographic north pole of the Earth.  Navigators refer to “magnetic north” as the geographic region toward which the north-seeking pole of a magnet points.  In fact, however, the magnetic pole now located somewhere in the Arctic Ocean must logically be a “south” magnetic pole of the magnet we call Earth, since north-seeking poles are attracted to it.  And, the other magnetic pole, located in Antarctica, must logically be a “north” magnetic pole. Because the magnetic poles of the Earth are not located exactly at the geographic poles, a correction is made to a compass reading if a navigator needs to be precise about the direction.  And, of course, near the poles of the Earth, a compass is of little value for finding direction. The use of the magnetic compass enabled ships to sail out of sight of land.  With the compass, explorers could travel to areas of the world previously unknown to them.  Trade across great oceans began.  Better and better maps were drawn to aid navigation.  While sailors could use a clock to navigate from the position of the stars and the sun, they still needed the compass to determine the direction in which they were heading on cloudy days and nights. Set-up/Management Tips Prepare materials for distribution.  Student Activity Book (pgs. 13 – 16) includes instructions with pictures for building a compass. Build a demonstration straw compass ahead of time to help students when constructing their own compass. Prepare a storage area large enough to store the students’ compasses without being damaged.  One possibility is to remove the compasses from the cups and lay them side by side in a cardboard box.  Remove any objects from working areas that may interfere with the compass magnets (jewelry, spiral notebook, etc.) Keep compasses for Lesson 6. The compass needles in most inexpensive, commercially produced compasses are only weakly magnetized.  Because of this, it is possible for them to become demagnetized or even magnetized with reverse polarity (the north-seeking end of the needle becomes the south-seeking end) by being in close proximity to stronger magnets.  You can check easily to see if this has happened to a compass by laying several compasses out on a flat, nonmagnetic surface and observing which way they point.  Check the compasses ahead of time. A compass needle can be polarized by rubbing a stronger magnet along its length, but it is probably more useful to discuss with students what has happened.  This is a great opportunity for students to realize that it is the magnetic properties of the compass needle that make it point the way it does, not the paint or dye on one end of the “needle.” Literacy Support Students can write about other ways to make a compass. Scientific Vocabulary The following words are key vocabulary words that will be introduced in this lesson and reinforced throughout the unit: *compass *Geographic north-pole *South-seeking pole *electric *North-seeking pole *magnetic field