5.1 Rolling friction like sliding friction depends upon many factors. It is a system effect that involves the nature of the specimen and the rolling surface. The sliding friction force (F) is usually considered to be the sum of forces arising from deformations of surface features (F_s), from attractive forces (atomic, molecular, etc.) at contact points (F_a), and force from interaction of films and particulates on the rubbing surfaces (F_f):

The rolling friction force includes these force contributions plus effects from the relative stiffness of the contacting surfaces, the diameter (curvature) of the specimen, and other factors. Because there are so many factors involved in a rolling tribosystem, rolling resistance can best be quantified by an actual test of the specimen of interest on the intended rolling surface, as described in this test method.

5.2 There are countless applications where it is important to quantify the rolling characteristics of a particular spherical specimen on a particular rolling surface. The interlaboratory tests conducted for this test method were performed on hardened steel balls like those used in ball bearings. This test method could be used to assess the effect of different rolling surfaces on the rolling characteristics of balls for ball bearings. Conversely, it could be used as a quality control test on balls. Surface imperfections/defects/films, etc. on the balls can affect how they roll and thus the distance traveled on a common rolling surface.

5.3 Industrial applications of this test method can include assessing conveying surfaces for spherical or nearly spherical parts: check valve balls, cabinet knobs, Christmas ornaments, toilet floats, etc. Many medical devices use special shapes where rolling characteristics are a consideration. Similarly, many pharmaceutical products (pills) are spherical or nearly spherical in shape, and this test method can be used to assess rolling characteristics for conveying or other reasons such as size (mass) check.

5.4 Rolling friction of spherical specimens can be a consideration in countless sports (soccer, golf, lacrosse, etc.) and game applications (billiards, bocce, toys, etc.). This test method can be used to rank the rolling resistance of different ball compositions, masses, shapes, surface textures, design, stiffness, etc. Similarly, the test method can be used to assess the ease of rolling of balls on different playing or game surfaces.

5.5 This test method is applicable to spherical or mostly spherical food products. For example, it is common to use the rolling distance of apples, citrus fruits, nuts, etc. for size classification in marketing. These items are rolled down an angled surface and the rolling distance serves as a parameter for size determination (mass/diameter). Moreover, this test method can be used to assess the suitability of various rolling surfaces (such as carpet, metal, wood, etc.) for suitability in classification equipment. Additionally, it could also be used for food conveyance for spherical-shaped processed foods (gumballs, hard candy, meatballs, etc.)

5.6 Finally, this test method can be a valuable teaching tool for physics and tribology students. The equipment is simple, low-cost, and student proof. It can be used to demonstrate the concept of rolling friction and the factors that affect it.

1.1 This test method covers the use of an angled launch ramp to initiate rolling of a sphere or nearly spherical shape, referred to as the specimen throughout this document, on a flat horizontal plane, referred to as the rolling surface, to determine the rolling friction characteristics of a given spherical shape on a given surface.

1.1.1 Steel balls on a surface plate were used in interlaboratory tests (see Appendix X1). Golf balls on a green, soccer and lacrosse balls on playing surfaces, bowling balls on a lane, basketballs on hardwood, and marbles on a composite surface were tested in the development of this test method, but the test applies to any specimen rolling on any rolling surface.

1.1.2 The rolling friction of specimens on rolling surfaces is affected by many factors, including specimen’s stiffness, radius of curvature, surface texture, the presence of films on the surface, and the nature of the rolling surface. This test method takes all of these factors into consideration. The specimen of interest is rolled on the rolling surface of interest using a standard ramp to initiate rolling and standard techniques are used to measure and treat the rolled distance after leaving the ramp.

1.1.3 This test method produces a rolling resistance number for a specific specimen on a specific rolling surface. It is intended for comparing similar tribosystems. For example, the rolling resistances of marbles on a particular surface are not to be compared with the rolling resistance of soccer balls on grass, because their masses and diameters are very different as are the rolling surfaces on which they roll.

1.1.4 Different launch ramps are appropriate for different types of specimens. If a specimen of interest cannot be accommodated with using one of the launch ramps discussed in Appendix X1 and Appendix X2, a different launch ramp can be developed and added with future revisions to this test method.

1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.