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Published in Dag K. Brune, Christer Edling, Occupational Hazards in the Health Professions, 2020
Lever action can be illustrated by a rod or pole hinged around a pivot point, a fulcrum. A force applied causes the lever to rotate. The turning action is determined by the turning moment, or torque, which is equal to the length of the lever arm multiplied by the force component perpendicular to the lever, or equivalently, the force multiplied by the perpendicular distance to the pivot point (Figure 1). Because of the multiplying action of the lever, either a gain in force or in distance can be accomplished. One can say that “what is gained in force is lost in distance” and vice versa. For a given force, a longer lever gives a larger turning moment than a shorter one. The lever is one of the simplest machines known.
Electrical science and principles
Published in Trevor Linsley, Electrical Installation Work Level 2, 2019
A lever allows a heavy load to be lifted or moved by a small effort. Every time we open a door, turn on a tap or tighten a nut with a spanner, we exert a lever-action turning force. A lever is any rigid body which pivots or rotates about a fixed axis or fulcrum. The simplest form of lever is the crowbar, which is useful because it enables a person to lift a load at one end which is greater than the effort applied through his or her arm muscles at the other end. In this way the crowbar is said to provide a ‘mechanical advantage’. A washbasin tap and a spanner both provide a mechanical advantage through the simple lever action. The mechanical advantage of a simple lever is dependent upon the length of lever on either side of the fulcrum. Applying the principle of turning forces to a lever, we obtain the formula:
Levers
Published in Paul Grimshaw, Michael Cole, Adrian Burden, Neil Fowler, Instant Notes in Sport and Exercise Biomechanics, 2019
Levers are classified into one of three types. These are termed first-, second- or third-class levers. A first-class lever is when the force and the resistance are located at separate sides of the fulcrum. A second-class lever is when the force and the resistance are located on the same side of the fulcrum. In this case the force is further away (at a greater distance) from the fulcrum than the resistance. A third-class lever is similar to the second-class lever (with the force and resistance on the same side from the fulcrum position) but this time the force is nearer to the fulcrum than the resistance. In the first-class lever system the distances of the force and the resistance that act either side of the fulcrum do not need to be equal. Figure C4.2 shows the three lever systems in more detail.
The influence of anthropometric variables, body composition, propulsive force and maturation on 50m freestyle swimming performance in junior swimmers: An allometric approach
Published in Journal of Sports Sciences, 2021
Marcos A. M. dos Santos, Rafael S. Henrique, Marlene Salvina, Artur Henrique Oliveira Silva, Marco Aurélio de V. C. Junior, Daniel R. Queiroz, Michael J. Duncan, José A. R. Maia, Alan M. Nevill
Prior research has also suggested that a larger arm span positively influences swimming performance due to a larger stroke length improving swimming efficiency (Moura et al., 2014; Toussaint & Hollander, 1994). The results of the present study only partially support this assertion as arm span was only influential in explaining 50 m freestyle performance only for girls, but not for boys. The advantage of having a greater arm span is fairly obvious in that this segment acts as a paddle, providing the swimmer a greater lever to propel through water. A longer lever length increases reach and the distance available for generation of propulsion, countering the greater energy requirement of using fewer strokes (Moura et al., 2014; Nevill et al., 2015). It is also possible that during adolescence there is an intense spurt in stature growth (peak height velocity, PHV), and sex differences are observed concerning PHV timing that occurs, on average, 2 years earlier in girls (~12 years) than in boys (~14 years). It is then possible to speculate that these differences may also contribute to this association (Gasser et al., 2001; Hauspie & Roelants, 2012). Additionally, growth spurts also occur in different segments of the body and these events are not synchronous. For example, on average, maximum speed in growth is achieved three-quarters of a year later for the trunk than for the legs or arms (Beunen & Malina, 1988; Gasser et al., 1991).