Box2d:negative value return from GetLinearVelocity();

When I use the following, somet开发者_StackOverflow中文版imes I get a negative value in mmVelik.x and mVelik.y. Can anyone explain why??

b2Vec2 mVelik = ballBody->GetLinearVelocity();

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If the value couldn't be negative, then objects would only be able to move in one direction. If the x value is positive, the velocity is toward the right, if it's negative, then toward the left. And ditto for the y value (down/up).