The Earth sits inside two invisible fields. Switch between them, drag the probe around the planet, and learn to read a field diagram like a physicist.
Distance from centre
Field strength
Pull direction
How to judge strength from a diagram
Look at the spacing of the field lines: where the lines are closer together, the field is stronger. Both fields are strongest near the Earth's surface and get weaker as you move away. Try dragging the probe further out and watch the numbers fall.
Same planet, very different fields
ShapeGravitational field lines point straight in towards the centre of the Earth. Magnetic field lines form loops that run from pole to pole.
What they act onGravity pulls on every object with mass. Magnetism only acts on magnetic materials and other magnets.
Pull or pushGravity only ever attracts. A magnetic field can attract or repel.
PolesThe magnetic field has two poles, north and south. The gravitational field has no poles at all.
One surprise for the curious: the Earth behaves as if a giant bar magnet sits inside it, and the magnetic pole under the Arctic is actually a magnetic south pole. That is why the north end of a compass needle points that way.
Check yourself
1. How can the strength of a field be judged by looking at a diagram of the field lines?
By the spacing of the lines. Where the field lines are drawn closer together the field is stronger, so both fields are strongest at the Earth's surface and weaker further away.
2. What difference between the two fields can you see on the diagrams?
Their shape and direction. Gravitational field lines point straight in to the centre of the Earth from every direction. Magnetic field lines loop round from one pole to the other.
3. What other differences exist between the fields, not shown on the diagrams?
Gravity acts on every mass and only ever attracts. Magnetism only affects magnetic materials and other magnets, and it can repel as well as attract. The magnetic field has two poles while the gravitational field has none.