Gravitational Field Lines
Gravitational Field Lines
- A field line turns an invisible field into a direction picture.
- Read the arrow first, then compare the spacing of nearby lines.
Field lines show direction and strength
- A field is present at many points in space. A shows the field direction at every point along the line.
- The arrow gives the direction. The line continues through the field; it is not one force arrow at one point.
- For gravity, every arrow points towards the mass that makes the field.
- The spacing compares field strength. Lines close together show a stronger field; lines farther apart show a weaker field.
The field around a planet
- Around a whole spherical planet, the field is : every line points towards the centre. The lines spread apart with distance, so the field becomes weaker.
- Now look at only a small area near the surface. The curved radial lines look almost parallel and evenly spaced. Over that small area, the field is almost : its size and direction change by a very small amount.
- For a point outside a , we can calculate the pull by putting all of the sphere's mass at its centre. Therefore, distance is measured from the centre.
Two facts from a field-line picture: arrows give the direction of the force on a mass; spacing gives the strength. The field is radial around the whole planet and almost uniform over a small area near its surface.