There are many types of shears used to shear sheet metal. Stability is determined by the balance of shear stress and shear strength. Vertical speed changes greater than also qualify as significant wind shear for aircraft. The maximum shear stress theory is conservative. Such stresses can be either shear or normal in nature. Despite the presence of vertical wind shear, convection became more concentrated. Downbursts create vertical wind shear or microbursts, which are dangerous to aviation. Another example of a shear thinning fluid is blood. The depression moved slowly westward in an environment of strong vertical shear. Von Willebrand factor is mainly active in conditions of high blood flow and shear stress. This does not take into account vertical wind shear. These definitions are consistent with those of normal stress and shear stress. Pure polycrystalline magnesium is brittle and easily fractures along shear bands. Normal blood plasma behaves like a Newtonian fluid at physiological rates of shear. These coatings have been described as shear thickening fluids.