Medical Physics Lecture 2 PDF

Medical Physics Lecture. 2 (part1) Forces on and in the Body Dr. Sara Ahmed Medicine & Dental College Stage 1 Forces on and in the Body o Forces on and in the Body: The force controls all motion in the world, the important force in the body is the muscular forces that cause the blood to circulate...

Medical Physics Lecture. 2 (part1) Forces on and in the Body Dr. Sara Ahmed Medicine & Dental College Stage 1 Forces on and in the Body o Forces on and in the Body: The force controls all motion in the world, the important force in the body is the muscular forces that cause the blood to circulate and the lungs to take in air and other. The physicists consider the very fundamental forces described as: - Gravitational force - Electrical force - Nuclear force (strong and weaker nuclear force) From Newton law: There is a force of attraction between any two objects 𝐹 = 𝑚. 𝑔 Where: g = acceleration due to gravity (𝑚/𝑠𝑒𝑐 ! or c𝑚/𝑠𝑒𝑐 ! ). m = the mass (𝑘𝑔, 𝑔). F = the force (𝑁𝑒𝑤𝑡𝑜𝑛, 𝑑𝑦𝑛𝑒). Our weight is due to the attraction between the earth and our bodies. The medical effect of gravitational force is the formation of varicose veins in the legs as the venous blood travels against the force of gravity on its way to the heart. Varicose veins are veins that have become enlarged and twisted. The term commonly refers to the veins on the leg, although varicose veins can occur elsewhere. Veins have pairs of leaflet valves to prevent blood from flowing backwards. Leg muscles pump the veins to return blood to the heart, against the effects of gravity. When veins become varicose, the leaflets of the valves no longer meet properly (as illustrated in figure.1), and 1 Medical Physics Lecture. 2 (part1) Forces on and in the Body Dr. Sara Ahmed Medicine & Dental College Stage 1 the valves do not work. This allows blood to flow backwards and they enlarge even more. Varicose veins are most common in the superficial veins of the legs, which are subject to high pressure when standing. Besides being a cosmetic problem, varicose veins can be painful, especially when standing. Figure 1: Shows the cause of varicose veins o The electrical force: This force is more complicated than gravity since it involves attractive and repulsive forces between static electrical charges as well as magnetic produced by moving electrical charges (electric currents). The electrical forces are immense compared to gravitational force, for example the electrical force between an electron (e-) and a proton (P+) in hydrogen atom is about 1039 times greater than the gravitational force between them. 2 Medical Physics Lecture. 2 (part1) Forces on and in the Body Dr. Sara Ahmed Medicine & Dental College Stage 1 o Nuclear forces: These forces counteract the enormous Coulomb’s repulsion of the positively charged “protons” and hold them together inside the nucleus. There are two types of nuclear forces: i) Strong nuclear forces: The strong nuclear force acts as the ''glue'' to hold the nucleus together against the repulsive forces produced by the protons on each other. ii) Weak nuclear forces: associated with electron decay from the nucleus (It may be related to the electrical forces). There are two types of problems involving forces on the body: those where the body is in equilibrium (statics) and those where the body is accelerated (dynamics). Statics (equilibrium). - Stationary (static) object is in the state of equilibrium - Translational equilibrium: (the sum of force in any direction is zero) 3𝐹 = 0 - Rotational equilibrium: (the sum of the torque about any axis is zero) 3𝜏 = 0 𝜏 = 𝐿 × 𝐹 where τ: The torque (N.m) F: The force (N) L: The vertical distance from the fulcrum point to the line (m, cm) action of the force 𝜏 "# = 𝜏 ""# Sum of clock wise torque= sum of counter clock wise torque 3 Medical Physics Lecture. 2 (part1) Forces on and in the Body Dr. Sara Ahmed Medicine & Dental College Stage 1 o Types of Levers in the Body Many of the muscle and the bone systems of the body acts as levers, Levers are classified according to the positions of the fulcrum, effort and load or resistance. There are three classes of levers, Identify as first, second, and third class levers. All these classifications depend on: 1. The force you apply (or the effort you make). 2. An opposing force such as a weight, which is usually called the load. 3. The pivot point, or fulcrum of the action. o Bones as Levers Each of the three types of levers can be found in the human body.In each type of lever, notice where the fulcrum is located compared to the effort and the load. In your body, the effort is the force that your muscles apply to the lever. The load is the weight that resists the pull of your muscles. • First Class Lever In a first class lever, the weight and force are on opposite sides of the fulcrum: Figure 2 4 Medical Physics Lecture. 2 (part1) Forces on and in the Body Dr. Sara Ahmed Medicine & Dental College Stage 1 An Examples of a first-class lever is the joint between the skull and the atlas vertebrae of the spine: the spine is the fulcrum across which muscles lift the head. Figure 3. • Second Class Lever In the second class lever, the load is between the fulcrum and the Forcen. Figure 4. 5 Medical Physics Lecture. 2 (part1) Forces on and in the Body Dr. Sara Ahmed Medicine & Dental College Stage 1 An example in the human body of a second-class lever is the Achilles tendon, pushing or pulling across the heel of the foot. Figure 5. • Third Class Lever In the third class lever, the force is between the fulcrum and load. Figure 6 6 Medical Physics Lecture. 2 (part1) Forces on and in the Body Dr. Sara Ahmed Medicine & Dental College Stage 1 An example of a third-class lever in the human body is the elbow joint: when lifting a book, the elbow joint is the fulcrum across which the biceps muscle performs the work. Figure 7. 7