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Water Hydraulics
Published in Frank R. Spellman, Handbook of Water and Wastewater Treatment Plant Operations, 2020
Water exerts force and pressure against the walls of its container, whether it is stored in a tank or flowing in a pipeline. Force and pressure are different, although they are closely related. Force is the push or pull influence that causes motion. In the English system, force and weight are often used in the same way. The weight of a cubic foot of water is 62.4 lb. The force exerted on the bottom of a one-foot cube is 62.4 lb. If we stack two cubes on top of one another, the force on the bottom will be 124.8 pounds. Pressure is a force per unit of area. In equation form, this can be expressed as: P=FA
Generation
Published in Joel L. Plawsky, Transport Phenomena Fundamentals, 2020
In momentum transport the generation terms result from forces acting to drive the fluid. Most commonly, these are pressure forces, body forces such as gravity, or surface forces. These forces accelerate or decelerate the fluid and so generate momentum in the system. Though we often think of body forces as just the force of gravity on the fluid (fluid statics), there are other examples. In natural convection, heat and momentum transport interact through density changes in the fluid causing fluid motion. Hot fluid, which is less dense, sees a buoyant force that accelerates it and causes the fluid to rise. Cold, denser fluid feels an opposite force and sinks. These buoyant forces are formally generation and involve not only gravity but also the temperature gradient. In magneto-hydrodynamics, small metal particles are mixed with the fluid and the system is placed in an electromagnetic field. The interaction of the field with the particles generates a force on the fluid that accelerates the fluid.
Dialectics of Nature: Inspiration for Computing
Published in Nazmul Siddique, Hojjat Adeli, Nature-Inspired Computing, 2017
Isaac Newton (1643–1727) published his three laws of motion in his book Mathematical Principles of Natural Philosophy in 1687 (see Newton, 1999). The three physical laws laid the foundation of classical mechanics, which describe the relationship between a body and the forces acting upon it, and its motion in response to said forces. The laws cover the law of inertia, the law of force, and the law of action and reaction. The first law of inertia states that if a body is at rest or moving at a constant speed in a straight line, it will remain at rest or keep moving at constant speed in the same direction. The second law of force states that the acceleration a (also defined as the rate of change of velocity) is directly proportional to applied force F and inversely proportional to mass m of the body. The third law also referred to as the law of action and reaction states that every action has an equal and opposite reaction.
RESNA position on the application of dynamic seating
Published in Assistive Technology, 2021
Michelle L. Lange, Barbara Crane, Frederick J. Diamond, Suzanne Eason, Jessica Presperin Pedersen, Greg Peek
Dynamic, in the context of physics, is defined as “of or relating to physical force or power” and “marked by usually continuous and productive activity or change” (Merriamwebster.com, 2019). Force is a vector, embodied by magnitude and direction. A wheelchair user exerts force onto a dynamic component in a specific direction or directions at a certain magnitude. Work results from forces acting upon an object and can either cause or hinder motion. Within dynamic seating, the individual is imparting “work” on the dynamic component, resulting in its displacement or movement. Power is the rate of performing work and is represented by work/time. A person provides more power when displacing the dynamic component rapidly rather than slowly. The dynamic motion imparts kinetic energy into the system. As the dynamic components displace, the kinetic energy is stored as potential energy, typically by displacing springs or polymers. This potential energy allows the dynamic component to return to its original position when the force is removed.
Determination of optimum post embedment depth for C120 steel posts using field and full scale crash test
Published in International Journal of Crashworthiness, 2019
Ali Osman Atahan, Murat Büyük, Murat Örnek, Musab Erdem, Yakup Turedi
A total of 20 one 4 mm thick S355JR quality C120 × 60 × 25 posts were used in the field tests. The yield and ultimate stress levels for these posts are 355 and 540 MPa, respectively. As shown in Table 3, PED was ranged from 650 to 900 mm for all three soil conditions. Classification of soft/medium/hard soil properties are based on values in Tables 1 and 2. In this table from the test codes, the letter gives the soil types and the numbers indicate the PED values. Posts were driven into the soil using a post installation machine and a picture of the installation procedure is shown in Figure 4. To deliver the impact forces to the posts, a 1000 kg pendulum device was used. The pendulum was raised 1.5 m using an electric motor and impacted C120 posts about 550 mm above ground level. This distance represents bumper height of an average small car. In this test setup, pendulum applied 14.7 kJ of kinetic energy to C120 posts. A picture of the pendulum used in this study is shown in Figure 5. An accelerometer was installed on the pendulum to measure the acceleration–time history during impact. This history is used to calculate velocity–time and eventually displacement–time histories. The force is calculated based on mass times measured acceleration. Eventually force–displacement history is obtained from all 21 impact cases. The area under these curves represented the work done, in other words, the energy absorbed by the post–soil interaction.
Determination of safety factors for structural bamboo design applications
Published in Architectural Engineering and Design Management, 2022
Lorena Sánchez Vivas, Kelly Costello, Sarah Mobley, James R. Mihelcic, Gray Mullins
Over the past 50 years, there has been a transition from empirical to statistically based design methodologies. The underlying fundamental premise of all designs is simple: the load on a structure should always be less than the strength of the structure. Elements within a structure can be exposed to compression, tension or shearing forces or can be subjected to bending which is technically not a force, but is caused by forces. Depending on the material type, the strength (breaking stress) may vary for these types of loads. For instance, the tensile strength of concrete is on the order of 1/10 the compression strength and shear strengths can be ¼–½ the axial strength.