Contact angle a contact angle of 0°. This is often the case for water on bare metallic or ceramic surfaces, although the presence of an oxide layer or contaminants on the solid surface can significantly increase the contact angle. Generally, if the water contact angle is smaller than 90°, the solid surface is considered hydrophilic and if the water contact angle is larger than 90°, the solid surface is considered hydrophobic. Many polymers exhibit hydrophobic surfaces. Highly hydrophobic surfaces made of low surface energy (e.g. fluorinated) materials may have water contact angles as high as ~120°. Some materials with highly rough surfaces
61 cm Type 90 torpedo 61 cm Type 90 torpedo The 61 cm Type 90 torpedo was a surface-fired torpedo used by the Imperial Japanese Navy during World War II. It was used in the s and in most cruisers, including the , , , and heavy cruisers after refits during the 1930s. It was superseded by the Type 93 oxygen-powered torpedo, commonly called the "Long Lance", as oxygen generating equipment was installed aboard the cruisers. The torpedo was based on a newly developed British Whitehead torpedo. This weapon used a new double-action two-cylinder engine rather than the four-cylinder radial engine used by World War