diff --git a/src/pendulum/drawing.ts b/src/pendulum/drawing.ts
index b50d8ca..a8f5c46 100644
--- a/src/pendulum/drawing.ts
+++ b/src/pendulum/drawing.ts
@@ -80,13 +80,17 @@ export function drawConstraint(ctx: CanvasRenderingContext2D, ball1: BallState,
 
 export function drawWorld(ctx: CanvasRenderingContext2D,
     world: PhysicalWorldState,
-    ballDrawers: BallDrawer[]
+    ballDrawers: BallDrawer[],
+    {
+        showForces = false
+    } = {}
 ) {
     for (const constraint of world.constraints) {
         const b1 = world.balls[constraint.p1Idx];
         const b2 = world.balls[constraint.p2Idx];
         drawConstraint(ctx, b1, b2);
         // Draw force vectors for debugging
+        if (!showForces) continue;
         const scale = 100; // Scale for visibility
         if (constraint.p1ConstraintForce) {
             ctx.beginPath();
diff --git a/src/pendulum/mod.tsx b/src/pendulum/mod.tsx
index 5b40a22..6a1178c 100644
--- a/src/pendulum/mod.tsx
+++ b/src/pendulum/mod.tsx
@@ -7,6 +7,7 @@ export default function Pendulum() {
   const canvasRef = useRef<HTMLCanvasElement>(null);
   const [subStep, setSubStep] = useState(10); // number of sub-steps per frame
   const [constraintIterations, setConstraintIterations] = useState(1); // number of constraint iterations per sub-step
+  const [showForces, setShowForces] = useState(false); // whether to show constraint forces
 
   // refs to hold pendulum instances and animation state so we can reset from UI
   const worldRef = useRef<WorldState | null>(null);
@@ -45,7 +46,9 @@ export default function Pendulum() {
       }
       ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
       if (worldRef.current) {
-        drawWorld(ctx, worldRef.current, worldRef.current.ballDrawers);
+        drawWorld(ctx, worldRef.current, worldRef.current.ballDrawers, {
+          showForces,
+        });
       }
       rafRef.current = requestAnimationFrame(animate);
     };
@@ -119,7 +122,7 @@ export default function Pendulum() {
       window.removeEventListener("pointermove", onPointerMove);
       window.removeEventListener("pointerup", onPointerUp);
     };
-  }, [constraintIterations, subStep]);
+  }, [constraintIterations, showForces, subStep]);
 
   // reset handler to re-create pendulums and avoid large dt on next frame
   const reset = () => {
@@ -159,6 +162,14 @@ export default function Pendulum() {
             className="ml-2 w-16 px-2 py-1 border border-gray-300 rounded focus:outline-none"
           />
         </label>
+        <label className="ml-4 text-sm">
+          디버그 힘 보기:
+          <input
+            type="checkbox"
+            onChange={(e) => setShowForces(e.target.checked)}
+            className="ml-2 w-4 h-4"
+          />
+        </label>
       </div>
       <div className="flex-1 min-h-0">
         <canvas