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Introduction
Published in B.K. Raghu Prasad, Structural Dynamics in Earthquake and Blast Resistant Design, 2020
A machine foundation supporting rotating machinery having an eccentric mass on the rotor will cause a sinusoidal force on the foundation. A tall building or a tall tower subjected to along and across wind oscillations is an example of sinusoidal load due to wind. The wind at certain velocities will cause resonant condition of the tower. Earthquake ground motion is an example of random base motion, which can cause severe damage to a structure if not properly designed. A distant blast or an explosion causes a triangular pulse load on a structure which is in the vicinity thus intercepting the over-pressure waves from the blast. Sudden fall of an object could be an example of an impulse. A suddenly applied load held constant over time can be a step load. Similarly, one can find examples of different types of pulse loadings. In all the examples cited above, the first mode natural period, T becomes important. Either the duration of the pulse in the case of pulse loads or the period of oscillation of the force in the case of sinusoidal load or reciprocal of the number of zero crossings per second in the case of random loading is compared with the natural fundamental period of the system. Their ratio is an important parameter which decides the severity of vibration.
Low-Gravity Environment
Published in Basil N. Antar, Vappu S. Nuotio-Antar, Fundamentals of Low Gravity Fluid Dynamics and Heat Transfer, 2019
Basil N. Antar, Vappu S. Nuotio-Antar
Third, forces due to the mass redistribution inside the spacecraft, that are transient in nature, also contribute to the total acceleration environment of specific bodies within the spacecraft. Prime examples of these are crew activities and the motion of mechanical parts. These forces do not involve any momentum changes of the spacecraft’s center of mass. Impulses caused by internal forces are always compensated for by equal and opposite impulses. All transient forces therefore result in an excitation of the flexibility modes of the spacecraft. The induced transient accelerations, called the g-jitter, are characterized by a broad frequency spectrum. Even though g-jitter may reach high peak values, the resulting displacements of particles with respect to the center of mass are small because of its compensated and random nature.
Centre of percussion
Published in Paul Grimshaw, Michael Cole, Adrian Burden, Neil Fowler, Instant Notes in Sport and Exercise Biomechanics, 2019
Now expressing this relationship to force applied, with respect to time or the integral of force and time, we get the following equation. And remember that this position can be calculated for a range of forces acting over a range of time periods. As force is applied to the object for a period of time, there will be an impulse that is applied to the object (see the Impulse and Momentum section in this text). As impulse is derived from the force applied and the time of application, the area that is contained under the force and time graph is the impulse. We know that impulse is defined as the change in momentum possessed by an object (Impulse = Ft = m(v2–v1)). In other words, an object or, in this case, the racket or bat, will achieve a greater final velocity (v2) if the impulse applied to the object is increased; assuming that the object starts off from a stationary position. Hence, if we take the integral (see the Kinematic Data: Integration section in this text) of this equation we can express this again as follows: v=(1m−A.bI)∫Ft
Relationships between highly skilled golfers’ clubhead velocity and kinetic variables during a countermovement jump
Published in Sports Biomechanics, 2022
Jack ET Wells, Andrew CS Mitchell, Laura H Charalambous, Iain M Fletcher
The change in momentum (mass x velocity) of a body is directly proportional to the application of impulse (force x time). Since mass remains constant during the golf swing, an increase in impulse, if transferred effectively, will directly increase the velocity of the distal segments (i.e., the clubhead). Recent research utilising force platforms has highlighted that CMJ positive impulse significantly related to highly skilled golfers’ CHV (r = 0.788, p < 0.001; Wells et al., 2018). This is also an important consideration when utilising jump height to assess golfers. For instance, assuming the same net impulse is applied to the system, an increase in mass will results in a reduced take-off velocity and therefore reduced jump height. Investigating the relationships between CMJ derived performance variables and CHV would help to support decision making for practitioners when profiling golfers. Consequently, the aim of this investigation was to assess the relationships between highly skilled golfers’ CHV and CMJ net impulse, positive impulse, peak power, average power, force at zero velocity, peak force and jump height. It was hypothesised that highly skilled golfers’ CHV would hold significant positive relationships with each of the variables measured during the CMJ.
Does the initial level of horizontal force determine the magnitude of improvement in acceleration performance in rugby?
Published in European Journal of Sport Science, 2021
Juan Antonio Escobar Álvarez, Pedro Jiménez-Reyes, Filipe Almeida da Conceição, Juan Pedro Fuentes García
Some authors have noted that the horizontal component of the total ground reaction force (GRF) is the determinant parameter for sprint acceleration performance, regardless of the athletes’ level of ability (Morin et al., 2012; Morin et al., 2016; Morin, Edouard, & Samozino, 2011; Rabita et al., 2015). Athletes have to develop the ability to accelerate their body mass forward during a sprint, and this is related to the ability to produce and apply a large impulse onto the ground (Rabita et al., 2015). The magnitudes of mechanical properties related to sprinting ability have been explored through the linear force-velocity (F–V) and parabolic power–velocity (P–V) relationships (Cross, Brughelli, Samozino, & Morin, 2017b; Samozino, Rejc, Di Prampero, Belli, & Morin, 2012). The F-V profile in sprinting can be assessed using a validated and simple method in realistic conditions to determine the maximal theoretical force (F0), maximal theoretical velocity (V0), F-V slope, and maximal power (Pmax).
Relationships between highly skilled golfers’ clubhead velocity and force producing capabilities during vertical jumps and an isometric mid-thigh pull
Published in Journal of Sports Sciences, 2018
Jack E. T. Wells, Andrew C. S. Mitchell, Laura H. Charalambous, Iain M. Fletcher
The findings from this investigation indicate that CMJ peak positive impulse has the greatest relationship with golfers’ CHV. Greater force over a specified period of time will lead to an increase in impulse (force x time). Newton’s second law of motion suggests that impulse is proportional to a change in momentum (mass x velocity). Since a golfers’ mass will stay constant between shots, any increase in impulse and therefore momentum, will result in an increase in velocity which will ideally be transferred to the clubhead. Clearly a golfer’s ability to generate positive impulse is an important component relating to CHV. This would indicate that training modalities aimed at increasing impulse during slow SSCs may be preferential when designing future training programmes. Given the significant positive relationship between CHV and PF, the ability of a golfer to generate force with the lower body appears to be a key factor for generating greater CHV. Training modalities incorporating strength training or loaded jumps should be considered when designing a strength and conditioning training programme for golfers, since these exercises have been found to significantly increase PF and impulse (Cormie, McGuigan, & Newton, 2010).