Combined Gravitational Fields
Combined Gravitational Fields
- Each mass makes its own field.
- At one point, find each field separately, include its direction, and then add the fields.
Add the fields with directions
- Gravitational field is a vector. Two fields that point in the same direction add. Two fields that point in opposite directions subtract.
- Between two masses, the fields point towards different masses, so they point in opposite directions.
- Draw the arrows before using numbers. This prevents a sign error.
- For two identical masses, the fields have equal sizes at the midpoint, so the net field is zero there.
Sketch the field between identical spheres
- Choose a positive direction before drawing. Here, field pointing to the right is positive. Field pointing to the left is negative.
- At the left surface, the field points left, so the graph starts at .
- At the midpoint, the two fields have equal sizes and opposite directions. The graph crosses .
- At the right surface, the field points right, so the graph ends at .
- From the left surface to the midpoint, the negative field becomes smaller in size. The curve rises and becomes less steep.
- From the midpoint to the right surface, the positive field becomes larger. The curve continues to rise and becomes steeper.
- Check all three marked points and both parts of the curve (9702/41/O/N/25 Q3(c)).
Common mistake
Do not draw only a V-shape or a straight line. Each field follows an inverse-square relation, so the combined graph is curved.