Falling ball

The time required for a ball to fall a given distance in a fluid is probably the simplest and certainly one of the oldest viscosity tests (Stokes, 1851). Unfortunately, creeping flow around a sphere is very complex. Thus the falling ball is really an index test and requires a constitutive equation for complete analysis. Analyses of the flow have been made for inelastic (Gottlieb, 1979 Beris et al., 1985) and viscoelastic fluids (Hassager and Bisgaard, 1983 Graham et al., 1989). Usually an apparent viscosity based on the Newtonian analysis is reported. 

Because the flow is slow, this value usually corresponds well to the zero shear viscosity even for elastic, shear thinning liquids. A test, of course, is to see whether die same is obtained for several 

Like the falling needle, the falling ball viscometer can be sealed to [nevent evaporation and permit measurements to be taken at high pressure. 

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Plazek et al.t measured the viscosities of a poly(dimethyl siloxane) sample of = 4.1 X 10 over a range of temperatures using the falling-ball method. Stainless steel (P2 = 7.81 g cm" ) balls of two different diameters,... 

Falling ball viscometers are based on Stokes law, which relates the viscosity of a Newtonian fluid to the velocity of the falling sphere. If a sphere is allowed to fall freely through a fluid, it accelerates until the viscous force is exactly the same as the gravitational force. The Stokes equation relating viscosity to the fall of a soHd body through a Hquid may be written as equation 34, where ris the radius of the sphere and d are the density of the sphere and the hquid, respectively g is the gravitational force and p is the velocity of the sphere. 

Fig. 31. Falling ball viscometer. Lines /q and t are the timing lines for velocity deterrninations.

One measure of impact resistance is the laminate s mean break height (MBH) (102). In the standard test, there is a 50% probabiHty that a five-pound (2.27-kg) ball will not fall through a laminate if the ball is dropped at the MBH. Typical MBHs for 12 in. (- 30 cm) square laminates prepared with 30 mil (0.76 mm) thick interlayer are 10 ft ( -- 3 m) at 0°F (—18 C) and 15 ft ( -- 4.6 m) at 70°F (2I°C). Figure 2 shows a relationship between adhesion and falling ball penetration resistance measured at 2I°C. 

The pH is measured using a 4% aqueous solution. Viscosity is normally measured using Brookfield viscometer. Alternatively, a capillary-type viscometer or falling ball such as Hxppler may be employed. The type of viscometer used must always be noted. 

Fig. 3. Rate of viscosity reduction of cellulose nitrate on digestion in water at 132°C. The viscosities (falling-ball method) were determined in 12.2%...

Impact Resistance. Tests for impact resistance of porcelain enamels include falling weight tests such as a free-falling ball or a pendulum... 

Falling-ball rebound test, 244 Ferrocene-containing polybenzimidazole, 315... 

Falling ball Difficult for nontransparent fluids and for low-viscosity fluids... 

A method similar to the falling-ball method is the bubble method. A vial is filled with liquid, leaving sufficient room for a bubble that can equal the diameter of the vial. The vial is inverted and the time required for the bubble to pass two predetermined marks is determined. The viscosity will be directly proportional to the time required for the bubble to rise. 

FRANCIS, A. W. Physics 4 (1933) 403. Wall effects in falling ball method for viscosity. 

Evidence for the formation of gels from aPS systems is obtained from simple mechanical, (1.4.5) viscoelastic, (7.8) thermodynamic (1.6) and spectroscopic ( ) techniques. Simple tube tilting, falling ball methods and differential scanning calorimetry have been used to determine the phase diagrams for a number of systems. Viscoelastic measurements on the aPS-carbon disulfide system show that the low frequency response indicative of a... 

NITRATE REDUCTASE NITRITE REDUCTASE PHENOL HYDROXYLASE PROLINE DEHYDROGENASE PUTRESCINE OXIDASE PYRUVATE OXIDASE SALICYLATE 1-MONOOXYGENASE SUCCINATE DEHYDROGENASE SULFITE REDUCTASE XANTHINE OXIDASE Falling ball viscometry,... 

West Germany by letter dated 24 July 1973= Lackwolle E33 is a pressure-cooked modified collodion cotton of 12.0 to 12,2% N. Its stability is less than 2.5cc NO/g and its viscosity by falling ball method of a 33% soln in 90—100% butyl acetate soln is I60sec or by Hercules method. 15 — 18 centipoises... 

Falkenstein, K. von patented in 1892 the smokeless proplnt called Cibalite, See Vol 3 of Encycl, p C322-R Falling Ball Test as conducted at Kankakee Ordnance Works, Joliet, 111 employed a 8.33g ball for testing impact sensitivity of LA. See under Ball Drop Test in Vol 1, p A573-L... 

Falling ball test (Kankakee Ordnance Plant) 6 F6... 

Leviton, A. and Pallansch, M. J. 1960. Laboratory studies on high temperature-short time sterilized evaporated milk. I. Easily constructed eccentric falling ball type bomb microviscometers. J. Dairy Sci. 43, 1389-1395. 

Weber, W. 1956. Systematic investigation of falling ball viscometers with inclined tubes. Kolloid Z. 147, 14-28. 

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