Instructions for Students: Building "Terrabagga"
Overview: You will build a simulated planet with a magnetic
core. The core will consist of a battery with "donut" magnets taped
onto the ends, creating the equivalent of a larger bar magnet. The core will
be wrapped in a crumpled paper bag (the bulk of the "planet"). The
bag will be held shut by rubber bands, which will also serve as latitude and
longitude lines dividing the "planet" into eight segments. You
will use a magnetometer to determine which octant of the planet the north and
south magnet poles are beneath. You will record this info, then swap planets
with other groups and repeat the "finding the poles" process
on several different "planets".
Refer to our Terrabagga
photos page to see pictures of the stages of this procedure.
- The first step in building a world with a magnetic field in it is to create
the dipolar magnet that will go inside the world. Take the two magnets and
place them on top of each other so that the magnets are attracted to each
other. Now without flipping either magnet over, place the top magnet on the
top of the battery. Tape this magnet in place. Place the bottom magnet on
the bottom of the battery (remember, the side that was facing up, should
now be against the casing of the battery). Tape this magnet in place.
- Next turn the paper bag inside out. This creates a clean surface that will
be labeled later on. Work the bag by crumpling it and folding it.
- When the bag is turned inside out and is pretty workable, place your battery
(with the magnets taped on) inside the paper bag. It does not matter which
way the battery is facing. Work the paper bag around the battery to create
a nice smooth (fairly round) world. Try to center the battery/magnet in the
middle of the "planet". If one pole is too close to the surface,
the opposite pole may be buried too deeply to sense with the magnetometer.
You may wish to use the optional plastic bag to add extra padding to the "planet's" interior
to help center the magnetic core, or you may want to "double-bag" the "core" to
accomplish the same result (i.e. first wrap the plastic bag around the "core",
then surround both with the paper bag).
- Now it's time to put the rubber band markers on your world. The first rubber
band can just be placed wherever it's most needed to hold your world together.
Just stretch the rubber band around your world.
- Now stretch one more rubber band across your world. This rubber band should
meet at right angles with the first rubber band so that your world is now
split into 4 equal segments. Pick one of the intersections of your two rubber
bands to be the geographic north pole. Make sure the north pole is facing
- Now it's time to label parts of your world. Note that the rubber bands
make a "X" when looking down on the north pole. The four "branches" represent
four lines of longitude separated by 90°; the prime meridian at 0°,
90° west longitude, the international dateline at 180°, and 270° west
longitude (which is the same as 90 east longitude). Pick one of the two rubber
bands to label first (either one - it doesn't matter which you do first).
Use the marker to write a zero on the rubber band on one side of the North
Pole, then write "180" on the same rubber band on the opposite
side of the North Pole.
- Now turn your world so that you are looking at the prime meridian (the
line of zero longitude) with the "North Pole" up. Everything east
(right) of the prime meridian all the way to the international dateline is
the eastern hemisphere. Everything west (left) of the prime meridian all
the way to the international dateline is the western hemisphere. Label the
part of your (unlabelled) rubber band that lies in the eastern hemisphere
90 E, because it represents the longitude of 90 degrees east. Label the part
of that same rubber band that lies in the western hemisphere, 90 W, because
it represents the longitude of 90 degrees west.
- Next add the third rubber band to your world. This rubber band should stretch
across both of the other rubber bands meeting those rubber bands at right
angles. This rubber band is your world's equator, so it should be stretching
across the middle of your world. Once that rubber band is in place, label
that rubber band "equator". Everything above equator towards the
geographic north pole is the northern hemisphere and everything to the south
of the equator is the southern hemisphere. Your world should now have eight
- It's time to label the 8 segments. The segments in the northern hemisphere
should be labeled 1-4 with segment 1 being between 0 and 90 E. Segment 2
is then between 90 E and 180, segment 3 is between 180 and 90 W and segment
4 should end up being between 90 W and 0. The segments in the southern hemisphere
should be labeled 5-8 with segment 5 being below segment 1 and so on so that
segment 8 is below segment 4.
- Make up a name for your "planet". Write the "planet's" name
on the "planet" somewhere (at the geographic south pole would be
- Use your magnetometer to test where the magnetic north
pole of your world is. The magnetometer end labeled north should dramatically
point in where the magnetic north pole of your world is. Write the segment
number where you find the magnetic north pole of your world onto your
student worksheet. Follow a similar process to
locate the magnetic south pole of your "planet".
- Trade planets with another group. Use your magnetometer
to locate the north and south magnetic poles of several planets and record
that information on your worksheet.
The source of this material is Windows to the Universe, at http://windows2universe.org/ from the National Earth Science Teachers Association (NESTA). The Website was developed in part with the support of UCAR and NCAR, where it resided from 2000 - 2010. © 2010 National Earth Science Teachers Association. Windows to the Universe® is a registered trademark of NESTA. All Rights Reserved. Site policies and disclaimer.