Hanging Magnet Compass

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Introduction: Hanging Magnet Compass

About: I grew up in a small town in South Germany with a rich tradition in toy-making. Tinkering and playing takes me back to the great times I had as a kid inventing toys and games in my granddad's toy workshop. ...

We are working on an outdoor art piece that will interact with the Earth's magnetic field. Experimenting to gain a understanding of magnetic forces, we came across this very simple way to make a hanging magnetic compass needle out of only 5 pieces without any machining or tools involved. We carry it around to show us the directions of the invisible magnetic field lines that are all around us (and even inside us).

Step 1: Gather Your Materials

For this project we only use 5 materials and no tools other than scissors.

  • neodymium magnet. 3/8" diameter, 1/8" width (e.g. from Forcefield). Know that neodymium magnets are really strong, so we handle them carefully and keep them away from cards with a magnetic strip.
  • rubber O-Ring. 1/4" inside diameter, 7/16" outside diameter (hardware store)
  • 2 thin flat-head screws. #4 screws, 2.5 inches long. Drywall screws work, too (hardware store).
  • 12” of thin thread.
  • red and white nail polish or paint. Colored tape to mark the compass needle works too.

Step 2: Paint the Screws

Use nail polish or other paint to paint one of the screws red, the other one white and let the paint dry while you are working on the next steps. If you want to skip this step, you can also mark one screw with a piece of red tape instead of painting it.

Step 3: Tie the String Around the O-Ring

Cut off the end of the string close to the knot for a clean look.

Step 4: Carefully Stretch the O-Ring and Fit It Over the Magnet

This will work with any size round magnet, as long as you have an O-Ring that is slightly smaller than the magnet. For example, you can make big compass needles with larger magnets and screws. Because of their increased inertia, they align more slowly with the Earth's field.

Step 5: Complete Your Compass Needle by Attaching the Screws

Let the magnet hang from the string while holding it still with one hand. Now let go of the magnet and watch it align. Depending on whether there is metal or other magnets near by, the magnet will allign with metal objects around it or the Earth Magnetic field.

Find a place far from metal objects (outdoors works best) and let the magnet hang from the string. Stick the red needle on the side of the magnet facing North following the convention that the red end of a magnetic needle always points to Magnetic North.

Step 6: Take Your Mangetic Compass Out for a Spin

Notice that Magnetic North is different from Geographic North. So if you are in San Francisco and are facing Geographic North, Magnetic North would be slightly to your right (East) by about 14 degrees. This is where your compass needle would be pointing. Dependent on where you are on the world, the red end of needle will also be pointing down a little. As the magnetic field lines curve around the globe, they bend down towards North when you are North of the Equator.

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5 Comments

if instead of hanging the needle from the top of the O ring, you hang it from two threads at the sides, it will show the magnetic "dip" into the Earth at your location.

Nice work

2 replies

I hve been mystified as to why the device hanging vertically from a single string doesn't dip the expected amount but with two horizontal threads does. I think it is because the compass is suspended slightly off center and above the long axis of the screws so in the gravitational field it twists back toward the horizontal. I liken it to a pendulum rocking back and forth under gravity while subject to a magnetic field. The sum of the forces on the compass as it hangs by a single thread greatly reduces the dip.

Thanks! I really like your suggestion. The North end of the needle we made definitely points down, but not as much as you'd expect for San Francisco. I am now using two needles, hanging one from the top and one from the sides to get all parameters of the magnetic field.


National Oceanic and Atmospheric Administration, (NOAA) offers a crowdsourcing smartphone app that allows you to upload magnetic field data. It's fun to use and very educational.

https://www.ngdc.noaa.gov/geomag/crowdmag.shtml

https://www.ngdc.noaa.gov/geomag/crowdmag.shtml#apps

CrowdMag project, we explore whether digital magnetometers built in modern mobile smartphones can be used as scientific instruments. With CrowdMag mobile apps, phones all around the world send magnetometer data to us. At our server, we check quality of the magnetic data and make data available to the public as aggregate maps and charts.

hlo may i know why u r placing ur magnet in the y axis. if i will use two magnets and a wodden small sheet then placed two magnets on the ends of rectangular sheet then it will work or not