Gravitational Fields & Field Lines
Gravitational Fields & Field Lines
- A mass changes the space around it: any other mass placed nearby feels a pull. Physics calls the changed space a .
- A gravitational field is a field of force: a region where a mass experiences a force.
Field lines
- A field line shows the direction of the force acting on a (test) mass placed at that point. That sentence is the marked definition (9702/42/M/J/25 Q2(a)).
- The spacing carries the second piece of information: lines closer together mean a stronger field.
- Around a planet the field is radial: every line points at the centre, and the lines spread apart with distance, so the field weakens.
- The drawing mark: at least four straight lines, evenly spaced, arrows pointing into the planet (9702/42/M/J/25 Q2(a)(ii)).
Your turn— tap to reveal the worked answer (9702/41/O/N/23 Q1(a)(ii))
Explain why the gravitational field near the Earth's surface is approximately uniform. (9702/41/O/N/23 Q1(a)(ii))
Answer: any change in height is negligible compared with the Earth's radius, so the field lines are effectively parallel (and evenly spaced).
One field, two pictures: radial from far away, uniform close up. Every sketch mark in this topic comes from one of the two.