Protractor Protractor A protractor is a measuring instrument, typically made of transparent plastic or glass, for measuring angles. Most protractors measure angles in degrees (°). Radian-scale protractors measure angles in radians. Most protractors are divided into 180 equal parts. Some precision protractors further divide degrees into arcminutes. They are used for a variety of mechanical and engineering-related applications. One common use is in geometry lessons in schools. Some protractors are simple half-discs. More advanced protractors, such as the bevel protractor, have one or two swinging arms, which can be used to help measure the angle. A bevel protractor is a graduated
Vibrations of a circular membrane equation with zero boundary conditions, Due to the circular geometry of formula_1, it will be convenient to use cylindrical coordinates, formula_13 Then, the above equations are written as Here, formula_16 is a positive constant, which gives the speed at which transverse vibration waves propagate in the membrane. In terms of the physical parameters, the wave speed, c, is given by where formula_18, is the radial membrane resultant at the membrane boundary (formula_19), formula_20, is the membrane thickness, and formula_21 is the membrane density. If the membrane has uniform tension, the uniform tension force at a given radius, formula_22 may be