Medical Physics Summary (lec.1) PDF

Peaks Medical Academy Medical Physics Summary (lec.1) First Stage Forces on and in the Body A-Forces in the body are: 1-Gravitational force. 2-Electrical force. 3-Nuclear force. B-Forces on the body are: 1-Static forces. 2-Frictional forces. 3-Dynamics forces. A- Forces in the body 1- Gravitational...

Peaks Medical Academy Medical Physics Summary (lec.1) First Stage Forces on and in the Body A-Forces in the body are: 1-Gravitational force. 2-Electrical force. 3-Nuclear force. B-Forces on the body are: 1-Static forces. 2-Frictional forces. 3-Dynamics forces. A- Forces in the body 1- Gravitational force :Newton law: There is a force of attraction between any two objects. - Example:- our weight is due to the attractions between the earth and our bodies. The medical effects of gravitational force :a- The formation of varicose veins in the legs as the venous blood travels against the force of gravity on its way to the heart. b-The loss of some minerals of the bone. When a person becomes weightless (such as in an orbiting satellite), then some of the bone mineral is lost. ‫ھﻧﺎ ﯾﺣﺟﻲ ﻋن ان اﻟﺟﺎذﺑﯾﺔ ﺗﺳﺑب‬ ‫دواﻟﻲ اﻟﺳﺎق ﻻن اﻟدم اﻟورﯾدي راح‬ ‫ﯾروح ﻟﻠﻘﻠب ﻋﻛس ﺟﺎذﺑﯾﮫ اﻷرض و‬ ‫ھﺎي اﻟﺣﺎﻟﺔ اﻛﺛر ﺷﻲ ﻧﺷوﻓﮭﺎ ﻋﻧد‬ ‫اﻟﻧﺎس اﻟﻲ ﺗوﮔف ھواي‬ ‫ﺛﺎﻧﻲ ﺗﺎﺛﯾر ﻟﻠﺟﺎذﺑﯾﮫ ھو ﻓﻘدان ﺑﻌض‬ ‫ﻣن ﻣﻌﺎدن اﻟﻌظم و ﻧﺷوﻓﮭﺎ ﻋﻧد‬ ‫اﻟﻧﺎس اﻟﻲ ﺗﻔﻘد اﻟوزن‬ The main force acting on the body is the gravitational force 2- The Electrical force: This force is more complicated than gravity (why) since it involves attractive and repulsive force between static electrical charges. magnetic forces produced by moving electrical charges (electric currents). electrical force, though very much stronger than the Gravitational force by a factor 1039 - The forces produced by the muscles are caused by electrical charges attracting or repelling other electrical charges. 3- The nuclear force: Its acts as the force to hold the nucleus together against the repulsive forces produced by the protons on each other. We have two type 1- strong nuclear forces 2- weaker nuclear forces Forces in the body 1- Statics, where the body is in equilibrium. 2- Dynamics, where the body is accelerated. 3- Friction, is involved in both statics and dynamics. 1-Statics Force When objects are stationary (static) they are in a state of equilibrium Types of Levers in the Body Many of the muscle and the bone systems of the body acts as levers. 1-First Class Levers: They are least common in the body. The fulcrum point (F) is between the muscle force (M) and the weight (W) for example the head. 2-Second Class Levers: They are found more than 1st class levers. Here (W) is between (F)& (M). For example, standing on the toes. 3-Third Class Levers: They are most common in the body. Here (M) is between (F)& (W). For example, the arm in the elbow joint. Length of the muscle From the diagram we notes that: 1-At the rest of the muscle (resting length L), it is close to its optimum length for producing force. 2-At about half muscle length (1/2 L), it cannot shorten further and the force, that the muscle produce drops. 3-At stretch of about double length (2L), irreversible tearing of muscle take place. 2- Frictional forces A force which resists the motion between two surface (in contact) depended on the nature of the surface is independent on the area of the surface. Friction in the body Some diseases of the body, such as arthritis, increase the friction in bone joints. Friction plays an important role when a person is walking. Example :- If a disease of the joint exists, the friction may become significant. Synovial fluid in the joint is involved in lubrication to reduce this friction. The saliva we add when we chew food acts as a lubricant. If you swallow a piece of dry toast you become painfully aware of this lack of lubricant. All of the internal organs are lubricated by a slippery mucus covering to minimize friction. ‫ﻓﮭم ﻓﻘط‬ 3-Dynamics Force This force is important when the body is moving and hitting another body. It appears on the body where acceleration or deceleration is involved. ‫ھﻧﺎ ﯾﻛﻠك ھﺎي اﻟﻘوة ﻣﮭﻣﺔ ﻟﻣن ﺟﺳم ﯾﺗﺣرك و ﯾﺻطدم ﺑﺟﺳم اﺧر‬ ‫و ھﺎي ﺗﻌﺗﻣد ﻋﻠﻰ اﻟﺟﺳم ﻟﻣن ﯾﻛون ﯾﺎ اﻣﺎ ﺑﺣﺎﻟﺔ ﺗﺳﺎرع او ﺗﺑﺎطؤ‬ This force is used in the "Forensic Medicine". ‫ا ﻟط ب ا ﻟ ﺷرﻋﻲ‬ The Effects of the Acceleration:- 1- increase or decrease in the body's weight. 2- Change in internal hydrostatic pressure. 3- Distortion of the elastic tissues of the body. 4- The tendency of solids with different densities suspended in a liquid to separate. 5- At a large acceleration the body loss control because it dose not have adequate muscle force to work against the large acceleration. Peaks Medical Academy The End of Lec.1