@Override
    public boolean equals(Object o){
        if(! (o instanceof Mass))
            return false;
        Mass m= (Mass)o;
        boolean equalVelocity= myBody.getLinearVelocity().x==m.myBody.getLinearVelocity().x
                &&myBody.getLinearVelocity().y==m.myBody.getLinearVelocity().y;
       
        return m.getBody().m_mass==getBody().m_mass &&
                m.x==x &&
                m.y==y &&
                equalVelocity;
                
    }