Can I sign 'arc' with just one hand?
While you can trace an arc with one hand to show a specific trajectory (like a ball flying through the air), the general sign for the geometric shape of an arc uses both hands symmetrically.
Is this sign used for a 'story arc'?
For an abstract concept like a 'story arc', you would typically fingerspell A-R-C or use signs related to 'development' or 'progression'. The two-handed tracing sign is usually reserved for literal, physical arcs.
What is the difference between signing 'arc' and 'circle'?
For 'circle', your hands will continue the downward movement to meet at the bottom, closing the shape. For 'arc', the movement stops after tracing the top curve, leaving the bottom open.