Natural convection arises due to unequal heating and ................ force.

Explanation

**Step-by-Step Solution:**

1. **Understanding Natural Convection:**
- Natural convection is a process where fluid motion occurs due to differences in temperature within the fluid. This temperature difference leads to variations in density.

2. **Identifying the Cause of Fluid Motion:**
- In natural convection, the fluid motion is not caused by any external force or mechanical means. Instead, it arises from the buoyancy effects due to temperature differences.

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