China
Africa
Explore chapters and articles related to this topic
Kinetics of Particles
Published in M Rashad Islam, A K M Monayem H Mazumder, Mahbub Ahmed, Engineering Dynamics, 2022
M Rashad Islam, A K M Monayem H Mazumder, Mahbub Ahmed
An impact is a high force or shock applied over a short period when two or more bodies collide. Such a force or acceleration usually has a greater effect than a lower force applied over a proportionally longer period. The effect depends, critically, on the relative velocity of the bodies to one another. For example, a nail is pounded with a series of impacts, each by a single hammer blow. These high-velocity impacts overcome the static friction between the nail and the substrate. Although on a much larger scale, a pile driver achieves the same result by driving a pile into the soil. This method is commonly used during civil construction projects to make the foundations for buildings and bridges. Road traffic accidents usually involve impact loading, such as when a car hits a traffic bollard, water hydrant, or tree, the damage is being localized to the impact zone. If the force that the objects exert on each other is parallel to the path of motion and directed toward the center of gravity of each object, the objects undergo a direct central impact. Otherwise, it is called oblique central impact.
Engineering Mechanics
Published in P.K. Jayasree, K Balan, V Rani, Practical Civil Engineering, 2021
P.K. Jayasree, K Balan, V Rani
The line of impact of the two colliding bodies is the line joining the centers of these bodies and passes through the point of contact or point of collision. Before the impact, if the two bodies are moving along the line of impact, the collision is called as direct impact. Now consider the two bodies A and B having a direct impact as shown in Figure 4.49b. Let m1 = mass of the first body, u1 = initial velocity of the first body, v1 = final velocity of the first body, and m2, u2, v2 = corresponding values for the second body. According to the law of conservation of momentum, m1u1+m2u2=m1v1+m2v2
Rocking and kinematic analysis of two masonry church façades
Published in Koen Van Balen, Els Verstrynge, Structural Analysis of Historical Constructions: Anamnesis, Diagnosis, Therapy, Controls, 2016
L. Giresini, P.B. Lourenço, M.L. Puppio, M. Sassu
The geometrical dimensions and mechanical characteristics adopted are displayed in Table 1. Bouncing and sliding are considered negligible, being the block sufficiently slender (height to thickness ratio larger than 3). The equation of motion written by Housner (1963) is integrated by means of a MATLAB code with a 4th-5th order Runge-Kutta integration technique, implemented in the ODE45 solver (MATLAB INC.). The restitution coefficient is the ratio of the velocity after impact and velocity before each impact, representative of the loss of energy over rocking. The theoretical value of restitution coefficient, equal to e = 1 - 11.5 sin 2 , was considered, by assuming the simplification of rectangular block. An amplification of earthquake intensity is necessary, being the rocking block at height different from zero. For that, the amplification factor expressed to increase the pseudo-acceleration in the Italian codes is used (NTC2008):
Biomechanics and footwear research 1970–2000
Published in Footwear Science, 2023
An impact is defined as a collision between two objects. Impact forces in running relate to the forces observed during the foot-ground collision. Loading during running was evaluated by determining the magnitude of the impact peak of the vertical ground reaction force component (see Figure 2) (Bates, 1985; Cole et al., 1996). The impact peak was generally normalized to body weight to make between-subject or between-footwear comparisons. In terms of footwear, impact forces (i.e. impact peak of the vertical ground reaction force component) determine the load on the body. The magnitude of the impact force or load was found to be up to two times a runner’s body weight and so it was logical to assume that impact forces were hazardous and could cause injuries.
Experimental study on the rebound characteristics of oblique collision of ash particles and the influence of ammonium bisulfate
Published in Aerosol Science and Technology, 2022
Shihao Hu, Qi Yin, Yize Zhang, Kefa Cen, Hao Zhou
The process of ash particles depositing on the heat exchange surface can be simplified to the rebound process of the ash particles colliding with the target surface. When the particle is in contact with the impact plane, the forces on the particle include friction, thermophoresis, and surface forces. The surface forces are caused by adhesion and the van der Waals force (Abd-Elhady and Malayeri 2013). In collision dynamics, the restitution coefficient is a common parameter that reflects the energy consumption during impact. The definition of restitution coefficient e is the percentage of rebound velocity to incident velocity (Zhou et al. 2016): where and are the impact and rebound velocities of ash particles, respectively, is the kinetic energy of the incident particles (angular momentum is ignored), and is the energy dissipation during impact. According to Liu, Li, and Yao (2011), energy dissipation can be divided into two parts, first-contact energy loss and energy dissipation through damping effects (friction and adhesion) or plastic deformation. The first-contact energy loss is independent of the impact velocity. The energy loss caused by plastic deformation and damping effects is closely related to the impact velocity. When the collision is a perfect elastic collision, the coefficient of restitution is 1. When the ash particle dissipates all the kinetic energy and attaches to the target surface, the coefficient of restitution is 0.