Where the two surfaces meet, they form a contact angle, formula_5, which is the angle the tangent to the surface makes with the solid surface. The diagram to the right shows two examples. Tension forces are shown for the liquid-air interface, the liquid-solid interface, and the solid-air interface. The example on the left is where the difference between the liquid-solid and solid-air surface tension, formula_6, is less than the liquid-air surface tension, formula_7, but is still positive, that is