How to synchronize circle (with SKAction by SKShapeNode) to ball (by SKShapeNode)? - sprite-kit

Question

I try to synchronize circle (create with SKAction by SKShapeNode) to ball (create by SKShapeNode).
Here is this code. But it couldn't work well.
What should I do?
-(void)makeContents{
//make ground
UIBezierPath *groundPath = [UIBezierPath bezierPath];
[groundPath moveToPoint:CGPointMake(0,250)];
[groundPath addLineToPoint:CGPointMake(568,100)];
SKShapeNode *ground = [[SKShapeNode alloc] init];
ground.path = groundPath.CGPath;
[self addChild:ground];
//make ball
SKSpriteNode *ball = [SKSpriteNode spriteNodeWithImageNamed:#"ball.jpeg"];
ball.position = CGPointMake(10, 320);
ball.size = CGSizeMake(20, 20);
ball.physicsBody.dynamic = YES;
ball.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:3];
[self addChild:ball];
}
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
//make circle
UIBezierPath *circlePath = [UIBezierPath bezierPath];
[circlePath addArcWithCenter:ball.position radius:10 startAngle:0 endAngle:2*M_PI clockwise:NO];
circle = [[SKShapeNode alloc] init];
circle.path = circlePath.CGPath;
circle.strokeColor = [SKColor blackColor];
//this line added after first post.
circle.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:10 center:ball.postion];
[self addChild:circle];
//make action
SKAction *scale = [SKAction sequence:#[[SKAction scaleBy:0.1 duration:2],
[SKAction scaleBy:0 duration:0.01]]];
[circle runAction:[SKAction repeatActionForever:scale]];
}
Thank you in advance for your help.