Surface tension gases. The pressure inside an ideal (one surface) soap bubble can be derived from thermodynamic free energy considerations. At constant temperature and particle number, , the differential Helmholtz energy is given by where is the difference in pressure inside and outside of the bubble, and is the surface tension. In equilibrium, , and so, For a spherical bubble, the volume and surface area are given simply by and Substituting these relations into the previous expression, we find which is equivalent to the Young–Laplace equation when . For real soap bubbles, the pressure is doubled due to the presence of two
Solid surface injected into molds to produce various solid decorative design figures. Solid-surface manufacturing companies may be members of the trade organizations American Composites Manufacturers Association, ISFA (International Surface Fabricators Association, and ICPA (International Cast Polymer Association). These organizations identify the product under the "brand" of MasterCast Engineered Composites. Solid surface can also be moulded using dedicated moulds. For example free standing baths are manufactured using a 2-part mould tool which creates a cavity for the material to be poured into. Once the mould has been prepared for casting, the material is mixed and degassed in an automated casting machine. It is