Differences in the Kinematics of Restrained and Unrestrained Conditions of Opening for Two Sizes of Glass Jar

Abstract

BackgroundOpening glass jars has been noted to be particularly problematic for consumers, leading to many studies related to the opening process. However, most studies place restrictions on jar opening by forcing the jar to remain on the counter or by requiring a specific hand on the closure.ObjectiveThe objectives of this research were (i) to evaluate the effect of restrained and unrestrained conditions on kinematics of jar opening, (ii) to evaluate the effects of jar diameter on kinematics and (iii) to evaluate how user characteristics (e.g. hand size) are associated with kinematics.MethodsKinematic data were collected from 21 participants during two opening conditions using jars with two diameters. Condition 1 restrained the participant by requiring that the jar maintain contact with the counter during the opening procedure. Condition 2 was termed unrestrained and allowed the user to open the jar with no requirements on jar or hand location.ResultsWhen restrained to a counter, the closure hand produced significantly more rotation compared with the closure hand in the unrestrained condition. Differences were not found in the opening motions when comparing jar diameters. However, hand breadth and length were related to the magnitude of rotation of the closure hand.ConclusionsPlacing restrictions on the participant, the orientation or location of the jar aids data analysis but may yield results that are not indicative of the user's actual jar opening process. Impositions on user positioning should be carefully considered in studies investigating the opening process of glass jars. Copyright © 2012 John Wiley & Sons, Ltd.