Gravitational Equipotential Surfaces
- Equipotential lines (when working in 2D) and surfaces (when working in 3D) join together points that have the same gravitational potential
- These are always:
- Perpendicular to the gravitational field lines in both radial and uniform fields
- Represented by dotted lines (unlike field lines, which are solid lines with arrows)
- In a radial field (eg. a planet), the equipotential lines:
- Are concentric circles around the planet
- Become further apart further away from the planet
- In a uniform field (eg. near the Earth's surface), the equipotential lines are:
- Horizontal straight lines
- Parallel
- Equally spaced
- Potential gradient is defined by the equipotential lines
- No work is done when moving along an equipotential line or surface, only between equipotential lines or surfaces
- This means that an object travelling along an equipotential doesn't lose or gain energy and ΔV = 0
Gravitational equipotential lines in a non-uniform and uniform gravitational field
- The distinction between radial and uniform fields is an important one
- In a radial field (eg. a point charge), the equipotential lines:
- Are concentric circles around the charge
- Become further apart further away from the charge
- Remember: radial field is made up of lines which follow the radius of a circle
- In a uniform field (eg. between charged parallel plates), the equipotential lines are:
- Horizontal straight lines
- Parallel
- Equally spaced
- Remember: uniform field is made up of lines which are a uniform distance apart
Exam Tip
Remember equipotential lines do not have arrows, since they have no particular direction and are not vectors.
Make sure to draw any straight lines with a ruler or a straight edge.