Medical Physics BMED 1309 PDF

BMED 1309 24-9-2022 1 Why Physics ??III Dr. Loai Afana 2 Definition: Medical physics is, in general, the application of physics concepts, theories, and methods to medicine or healthcare. Dr. Loai Afana 3 Any quantity that g...

BMED 1309 24-9-2022 1 Why Physics ??III Dr. Loai Afana 2 Definition: Medical physics is, in general, the application of physics concepts, theories, and methods to medicine or healthcare. Dr. Loai Afana 3 Any quantity that gives both magnitude and direction is a vector (eg, a force) that can be described by a straight line. Quantities that involve only magnitude are referred to as scalars. 4 Physical quantities : Basic quantities : the three fundamental quantities are Length (L), mass (M), time (T) Derived quantities : all other physical quantities in mechanics can be expressed in term of basic quantities Velocity Area Volume. Acceleration Force Momentum Work ….. 5  Units Time > Second (s) The SI unit of time is the Second, which is the time required for a cesium-133 atom to undergo 9192631770 vibrations. Length > Meter (M) The SI unit of length is Meter, which is the distance traveled by light in vacuum during a time of 1/2999792458 second. Mass > Kilogram (kg) The SI unit of mass is the Kilogram, which is defined as the mass of a specific platinum-iridium alloy cylinder. 6  Systems of Units * SI units (International System of Units): length: meter (m), mass: kilogram (kg), time: second (s) *This system is also referred to as the mks system for meter-kilogram-second. * Gaussian units: length: centimeter (cm), mass: gram (g), time: second (s) *This system is also referred to as the cgs system for centimeter-gram-second. * British engineering system: Length: inches, feet, miles, mass: pounds, time: seconds We will use mostly SI units, but you may run across some problems using British units. You should know how to convert back & forth. 7  Conversions 1 mile = 1609 m = 1.609 km 1 ft = 0.3048 m = 30.48 cm 1 in = 0.0254 m = 2.54 cm 1pound=450g 1kilogram=2.20 pound (Lbs) 1m = 39.37 in = 3.281 ft 1 mile = 5280 ft Example: Convert miles per hour to meters per second !!?? 1mile 1609 m   0.447 m / s 1hour 3600 s Questions: 1. Convert 500 millimeters into meters. 500/1000 = 0.5m 2. Convert 4.2 liters into milliliters. 4.2 * 1000 = 4200 mil.L 3. Convert 1.45 meters into inches. 1.45 * 39.37 = 57.086 inch 4. Convert 65 miles per hour into kilometers per second. 65mil/1H * 1609m/3600s =0.029 Km/s = 29 m/s 8 Prefixes Prefixes correspond to powers of 10 Each prefix has a specific name/abbreviation Power Prefix Abbrev. 1015 peta P 109 giga G 106 mega M 103 kilo k 10-2 centi c 10-3 milli m 10-6 micro m 10-9 nano n 10-12 pico p 10-15 femto f 9 Example : Newton’s law of universal gravitation is shown by Mm FG r2 What are the SI units of the proportionality constant G? Here F is the magnitude of the gravitational, M and m are the masses of the objects, and r is a distance. 10  Density Density is the mass per unite volume of the material. M Every substance has a density, designated   V M Dimensions of density are,  units (kg/m3). L3  Some examples: And its units are gm/cm³ and pound/in³ Substance  (g/cm3) Gold 19.3 Aluminum 2.70 Water 1.00 lead 11.3 wood 0.3-0.9 steel 7.8 11  Example : A solid piece of lead has a mass of 23.94 g and a volume of 2.10 cm3. From these data, calculate the density of lead in SI units (kg/ m3). Exemple: What volume dose 300g of mercury occupy, note that density of mercury is 13600kg/m3. 16  Problem When mixing 300cm3 water with 600cm3gasoline, what is the density of the mix? ρ = 1000 kg/m3 ρgasoline = 739 kg/m3 W Dimensional Analysis 19 Dimensional Analysis Definition: The Dimension is the qualitative nature of a physical quantity (length, mass, time). brackets [ ] denote the dimension or units of a physical quantity: Quantity Dimension Length [L]=L Mass [M]=M [Q] Time [T]=T - If an equation is dimensionally correct, does Area [A] = L2 this mean that the equation must be true? Volume [V]=L3 - If an equation is not dimensionally correct, does this mean that the equation cannot be velocity [v]= L/T true? Acceleration [a] = L/T2 force [f]=M L/T2 Idea: Dimensional analysis can be used to derive or check formulas by treating dimensions as algebraic quantities. Quantities can be added or subtracted only if they have the same dimensions, and quantities on two sides of an equation must have the same dimensions. 20  Example : Show that the expression x = vt +1/2 at2 is dimensionally correct , Where: x is coordinate and has unit of length, v is velocity, a is acceleration, and t is the time. 21 Example: Which of the following equations are dimensionally correct? Where: (x, y, m) is unit of length, (v) is velocity, ( a) is acceleration (a ) v f  v i  ax (b ) y  (2m ) cos(kx ), where k  2m 1 22 Example: The position of a particle moving under uniform acceleration is some function of time and the acceleration. Suppose we write this position: x = kam tn where , k is a dimensionless constant. Use the dimensional analysis to determine the power n and m. 23 Example: A particle moving in circle of radius r with uniform velocity v, Suppose that the acceleration (a) of the particle is proportional to the rn and vm. Use the dimensional analysis to determine the power n and m. Dr. Loai Afana 25