BIO-PHYSICS

1. BIO-PHYSICS Dr. Mohamed Rashad Physics Department, Faculty of Science Assiut university 2011-2012

2. Dr. Mohamed Rashad Attention please Human Body Physics

3. First of all, you should to know !!!!!!!!!!!!!! • Plain and simple, biophysics is the physics of biology, just as astrophysics is the physics of astronomy and nuclear physics is the physics of atomic nuclei. • What does this mean? What is the physics of biology? • Physics is the study of matter and energy. • Biophysics tries to understand how the laws of matter and energy are at work in living systems. • Another way to say this is that biophysics uses of the principles, theories, and methods of physics to understand biology. • Biophysics is an interdisciplinary science. • One could say it is the place where physics, chemistry, biology, and mathematics all meet. • In practice, most biophysicists study things at the molecular level, but biophysics also includes physiological, anatomical, and even environmental approaches to the physics of living things.

4. Chapter 1. Equilibrium and Stability of the human body

5. Figure (1.1): Stability of bodies.

6. Figure (2): (a) Torque produced by the weight will restore the body to its original position. (b) Torque produced by the weight will topple the body.

7. 1.2 Equilibrium Considerations for the Human Body The center of gravity (c.g.) of an erect person with arms at the side is at approximately 56% of the person’s height measured from the soles of the feet (Fig. 1.3). Figure (1.3): Center of gravity for a person.

8. This tendency of the body to compensate for uneven weight distribution often causes problems for people who have lost an arm, as the continuous compensatory bending of the torso can result in a permanent distortion of the spine. It is often recommended that amputees wear an artificial arm, even if they cannot use it, to restore balanced weight distribution. Figure(1.4): A person carrying a weight

9. Chapter 4. Fluids

10. Force and Pressure in a Fluid Solids and fluids transmit forces differently. When a force is applied to one section of a solid, this force is transmitted to the other parts of the solid with its direction unchanged. Because of a fluid’s ability to flow, it transmits a force uniformly in all directions. Therefore, the pressure at any point in a fluid at rest is the same in all directions. The force exerted by a fluid at rest on any area is perpendicular to the area. A fluid in a container exerts a force on all parts of the container in contact with the fluid. A fluid also exerts a force on any object immersed in it. The pressure in a fluid increases with depth because of the weight of the fluid above. In a fluid of constant density ρ, the difference in pressure, P2 −P1, between two points separated by a vertical distance h is Fluid pressure is often measured in millimeters of mercury, or torr

11. Pascal’s Principle When a force F1 is applied on a surface of a liquid that has an area A1, the pressure in the liquid increases by an amount P (see Fig. 4.1), given by In an incompressible liquid, the increase in the pressure at any point is transmitted undiminished to all other points in the liquid. This is known as Pascal’s principle. Because the pressure throughout the fluid is the same, the force F2 acting on the area A2 in Fig. 4.1 is Figure (4.1): An illustration of Pascal’s principle. The ratio A2/A1 is analogous to the mechanical advantage of a lever.

12. Chapter 5. The Motion of Fluids

13. We will illustrate the use of Bernoulli’s equation with a simple example. Consider a fluid flowing through a pipe consisting of two segments with crosssectional areas A1 and A2, respectively (see Fig. 5.1). The volume of fluid flowing per second past any point in the pipe is given by the product of the fluid velocity and the area of the pipe, A×v. If the fluid is incompressible, in a unit time as much fluid must flow out of the pipe as flows into it. Therefore, the rates of flow in segments 1 and 2 are equal; that is, Figure (5.1): Flow of fluid through a pipe with two segments of different areas. In our case A1 is larger than A2 so we conclude that the velocity of the fluid in segment 2 is greater than in segment 1.

14. Viscosity and Poiseuille’s Law Frictionless flow is an idealization. In a real fluid, the molecules attract each other; consequently, relative motion between the fluid molecules is opposed by a frictional force, which is called viscous friction. Viscous friction is proportional to the velocity of flow and to the coefficient of viscosity for the given fluid. As a result of viscous friction, the velocity of a fluid flowing through a pipe varies across the pipe. The velocity is highest at the center and decreases toward the walls; at the walls of the pipe, the fluid is stationary. Such fluid flow is called laminar. Figure 5.2 shows the velocity profile for laminar flow in a pipe. The lengths of the arrows are proportional to the velocity across the pipe diameter. If viscosity is taken into account, it can be shown that the rate of laminar flow Q through a cylindrical tube of radius R and length L is given by Poiseuille’s law, which is Figure (5.2): Laminar flow. The length of the arrows indicates the magnitude of the velocity of the fluid.

15. Circulation of the Blood The circulation of blood through the body is often compared to a plumbing system with the heart as the pump and the veins, arteries, and capillaries as the pipes through which the blood flows. This analogy is not entirely correct. Blood is not a simple fluid; it contains cells that complicate the flow, especially when the passages become narrow. Furthermore, the veins and arteries are not rigid pipes but are elastic and alter their shape in response to the forces applied by the fluid. Still, it is possible to analyze the circulatory system with reasonable accuracy using the concepts developed for simple fluids flowing in rigid pipes. Figure (5.4): Schematic diagram showing various routes of the circulation.

16. Chapter 6. Electricity

17. The Nervous System The most remarkable use of electrical phenomena in living organisms is found in the nervous system of animals. Specialized cells called neurons form a complex network within the body which receives, processes, and transmits information from one part of the body to another. The center of this network is located in the brain, which has the ability to store and analyze information. Based on this information, the nervous system controls various parts of the body. The nervous system is very complex. The human nervous system, for example, consists of about 1010 interconnected neurons. It is, therefore, not surprising that, although the nervous system has been studied for more than a hundred years, its functioning as a whole is still poorly understood. It is not known how information is stored and processed by the nervous system; nor is it known how the neurons grow into patterns specific to their functions. Yet some aspects of the nervous system are now well known. Specifically, during the past 40 years, the method of signal propagation through the nervous system has been firmly established. The messages are electrical pulses transmitted by the neurons. When a neuron receives an appropriate stimulus, it produces electrical pulses that are propagated along its cablelike structure. The pulses are constant in magnitude and duration, independent of the intensity of the stimulus. The strength of the stimulus is conveyed by the number of pulses produced. When the pulses reach the end of the “cable,” they activate other neurons or muscle cells.

18. The Nervous System The Neuron The neurons, which are the basic units of the nervous system, can be divided into three classes: sensory neurons, motor neurons, and interneurons. The sensory neurons receive stimuli from sensory organs that monitor the external and internal environment of the body. Depending on their specialized functions, the sensory neurons convey messages about factors such as heat, light, pressure, muscle tension, and odor to higher centers in the nervous system for processing. The motor neurons carry messages that control the muscle cells. These messages are based on information provided by the sensory neurons and by the central nervous system located in the brain. The interneurons transmit information between neurons. Figure (6.1): A neuron.

19. Electricity in the Bone When certain types of crystals are mechanically deformed, the charges in them are displaced; as a result, they develop voltages along the surface. This phenomenon is called the piezoelectric effect (Fig. 6.11). Bone is composed of a crystalline material that exhibits the piezoelectric effect. It has been suggested that these piezoelectric voltages play a role in the formation and nourishment of the bone. The body has mechanisms for both building and destroying bone. New bone is formed by cells called osteoblasts and is dissolved by cells called osteoclasts. It has been known for some time that a living bone will adapt its structure to a long-term mechanical load. Figure (6.11): The piezoelectric effect.

20. Chapter 8. References Biophysics Auther: Daniel Goldfarb New york Chicago San Francisco Lisbon London Madrid Mexico City Milan New Delhi San Juan Seoul Singapore Sydney Toronto Third Edition, Physics in Biology and Medicine Auther: Paul Davidovits Academic Press is an imprint of Elsevier 30 Corporate Drive, Suite 400, Burlington, MA 01803, USA Fifth Edition, Physics For Scientists And Engineers Auther: Serway

21. With my best wishes Dr. Mohamed Rashad S. Ahemd Physics Department Email: mrashad776@gmail.com