Intro, Forces and Waves I - Week 1 Physics PDF

Week 1 – Physics Introduction and fundamentals of Physics Dr. Jasmina Isaković 8th October 2024 Introduction Dr. Jasmina Isaković Acting Vice Chair @ EUC School of Medicine – Frankfurt Branch Lecturer Histology & Embryology Physics for Biomedical Sciences Nano...

Week 1 – Physics Introduction and fundamentals of Physics Dr. Jasmina Isaković 8th October 2024 Introduction Dr. Jasmina Isaković Acting Vice Chair @ EUC School of Medicine – Frankfurt Branch Lecturer Histology & Embryology Physics for Biomedical Sciences Nanomedicine e-mail: [email protected] office hours: Monday: 16:00 – 16:40 Tuesday: 11:30 – 12:20 17:00 – 17:40 12:30 – 13:20 13:30 – 14:20 15:00 – 15:50 Attendance We are taking attendance using Microsoft Forms. In order to register as being present in today’s class please do the following: 1. Scan the QR code 2. Input your registration number, name and surname 3. Submit the form Physics is also called "the fundamental science" because all branches of natural science like chemistry and biology are constrained by laws of physics. Introduction and Fundamentals of physics Outline Physics in Medicine Standard Units Derived or Secondary Units Prefixes Scientific Notation Orders of Magnitude Distances and Sizes Vectors and Scalars Coordinate Systems Mass and Inertia Outline of the Assignment Physics in Medicine ✓ Basic knowledge of physical principles encountered in medicine background of physiological processes and as working principles of biomedical devices. ✓ Assess the risks connected with operation of diagnostic or therapeutic systems necessary to understand interaction of many physical agents with human body. ✓ Find new ways to advance medicine using the concepts and laws of physics Fundamentals of Physics Physicsts make observations and ask basic questions: How big is an object? How much mass does it have? How far did it travel? How do we answer these questions? We take measurements and express them in standard units. Why are standard units important? Why are standard units important? Why are standard units important? I. To measure the quantities accurately. II. To convey the measurements to other people so that they understand those measurements accurately and follow the same further. Why are standard units important? ANECDOTE Why are standard units important? ANECDOTE September of 1999. NASA’s Mars Climate Orbiter has spent 10 months on Mars. And then it burned and broke into pieces. Why are standard units important? ANECDOTE Problem: software controlling the orbiter’s thrusters. The software calculated the force that the thrusters needed to exert in pounds of force. A second piece of code that read this data assumed it was in the metric unit—“newtons per square meter”. Why are standard units important? ANECDOTE How did it happen? 1. The propulsion engineers at Lockheed Martin in Colorado expressed force in pounds. But, it was standard practice to convert to metric units for space missions. 2. Engineers at NASA’s Jet Propulsion Lab assumed the conversion had been made. Spacecraft ended up dangerously close to the planet’s atmosphere where it presumably burned and broke into pieces. Fundamentals of Physics Physical quantity Something that can be measured. Unit must be stated to give an understanding of the scale of the measurement Measured quantity always compared to an established standard. has PERMANENCE and REPRODUCIBILITY Standard Units Laws of physics expressed in terms of physical quantities. Physical quantity – something that can be measured. Every measurement or quantitative statement requires a unit. Scientists have agreed to use SI Units. It defines basic units for basic quantities of importance in nature. International System of Units (SI) Derived and Secondary Units Are derived from standard units.  Not all countries use the International System of Units (SI). USA one of the few countries that uses the imperial system. Prefixes Useful in expressing physical quantities that are very large or very small. Example: Estimate the area of Singapore as 716.1 km2 instead of 716100000 m2. Physics explains things that are very, very large. Physics explains things that are very, very small. Prefixes In medicine we study objects that span a wide range of sizes. The basic unit of length in the metric system is the meter (m). e.g. 1 meter is about the height of a 3 year old child. For objects much larger or smaller than a meter, we add a prefix: Rules for Scientific Notation Rules for Scientific Notation Rules for Scientific Notation Example 1 Order of Magnitude Powers of Ten™ (1977) (youtube.com) Order of Magnitude Many small structures of our body are of size: 1mm - 1μm. Distances and Sizes Human lungs: consist of a branching network of tubes through which air flows. These tubes end in small, nearly spherical air sacs called alveoli. Each alveolus has a diameter of about 200 μm with an increase diameter during inhalation. Conversion of Units Exercise 1 Convert the speed of 55 mi/h into meter per seconds. Exercise 2 The recommended tire pressure in a Honda Civic is 28 psi (pounds per square inch). What is the pressure in atmospheres (atm) ? 1 Pa = 1 N/m2 Vectors and Scalars Examples Vector - quantity with magnitude (size) and direction. Vectors: Scalars: Displacement Distance Scalar - quantity with magnitude only. Velocity Speed Acceleration Time Momentum Mass Negative & Positive Vectors Force Energy Negative vector is a vector which will always be in the direction opposite the reference position direction. Vectors are represented with arrows The length of the arrow represents the magnitude (how far, how fast, how strong, etc, depending on the type of vector). But where do we put these vectors? Coordinate Systems To determine the position of a moving or static object in the space, we need to know the coordinates. Rectangular or cartesian coordinates xy – coordinates which intercept perpendicularly at (0,0), origin point. Define any position of any point in the xy plane we write (x,y). Polar coordinates distance is determined by r, while the angle is measured by θ which need to be with respect to the x/axis. Determine any object by (r, θ). Do NOT forget: A+B = B+A A-B = A+(-B) A+(B+C)=(A+B)+C Coordinate systems Negative & positive vectors Negative vector is a vector which will always be in the direction opposite the reference position direction. Mass and Inertia Mass How hard is it for something to move Intimately related to the idea of inertia Distinct from weight, which relates to gravity. ❑Mass is conserved, and can only be rearranged Inertia The property of an object that is at rest or in motion to remain at rest or in motion Assignment Physics to a 5-year-old Outline of the Assignment Written assignment Assignment presentation What is the goal of the Assignment? Why is this important? Case 50-year old patient with no underlying conditions. Underwent MRI post fall. Diagnosed with ependymoma. Treatment options 1. Gamma knife 2. Surgery 3. Whole-brain radiation + chemo Why is this important? Medical opinion Due to location anand size, gamma knife is recommended. Patient is skeptical. Wants no surgery (?) Your role Help the patient make an informed decision! Example MRI to a 5-year old Example MRI to a 5-year old Example MRI to a 5-year old Example MRI to a 5-year old Example MRI to a 5-year old Thank you! Forces and Motion of the Human Body Outline Musculoskeletal System Forces Newton’s Laws Forces and the Human Body Gravity and Blood Circulation Gravity and Bone Health Adding Forces Net Force Translational Equilibrium Rotational Equilibrium Torque Equilibrium in Medicine Levers in the Human Body The Body: A Mobile Physics Lab ✓ Motion and balance ✓ Acoustics ✓ Fluids and pressure ✓ Optics ✓ Energy ✓ Electricity The musculoskeletal system is a structure and machine that provides balance and motion. Functions of the cardiovascular system (breathing and pulse) are governed by laws of fluids and pressure. The brain is a computer with an electrical connection called the nervous system. The Musculoskeletal System Its primary purpose is to provide movement for the body. It includes... Muscles – generate force Tendons – transfer force to bones Bones – move if enough force is transmitted Joints – allow bones to move In Biology, these components form the musculoskeletal system. In Physics, these components form a system of simple machines. Forces What are forces? Kick a ball and it'll fly up into the air before falling back down to the ground. That's an example of everyday forces. What exactly is a force? Definition of force A force is a pushing or pulling action that can make things move, change direction, or change shape. Forces have both a magnitude and a direction (i.e. they can be represented as vectors). They give rise to accelerations through Newton’s second law: F=ma Forces can be represented as vectors Newton’s Laws Newton’s First Law Every object continues in its state of rest or continues to move in a uniform speed in a straight line UNLESS it is compelled to change that state by a net force acting on the object Note what is not stated or implied by Newton’s first law: I. it does not mean that every moving object has a force acting on it. II. it does say that a stationary object has no forces acting on it. Newton’s Laws How do forces affect the body? We are aware of forces on the body such as the force involved when we bump into objects. We are usually unaware of important forces inside the body. Forces inside the human body: Muscular forces: cause the blood to circulate and the lungs to take in air. Molecular forces: force that determines if a particular atom or molecule will stay at a given place in the body. How do forces affect the body? Molecular forces For example, in the bones there are many crystals of bone mineral (calcium hydroxyapatite, HAp) that require calcium. A calcium atom will become part of the crystal if it gets close to a natural place for calcium and the electrical forces are great enough to trap it. It will stay in that place until local conditions have changed and the electrical forces can no longer hold it in place. This might happen if the bone crystal is destroyed by cancer.  Internal forces External forces 1. Gravitational force 1. Gravitational force 2. Electromagnetic forces 2. Static force 3. Strong and weak nuclear forces 3. Dynamic force Forces that act on one part of an object or Forces that act on an object or system system from another part of the same from outside of it. object or system. Can cause acceleration or Do not change the overall motion of the deformation of the object or system. object or system. Static: e.g. friction, static electricity Dynamic: e.g. electromagnetic, Forces in the body 1. Gravitational forces Newton’s Universal law of gravity. There is a force of attraction between any two objects ✓ Our weight is due to the attraction between the Earth and our bodies. 2. Electromagnetic forces Attractive and repulsive forces between static electrical charges as well as magnetic force produced by moving electrical charges (electrical current). Electrical forces are immense compared to gravitational force. For example, the electrostatic force between an electron and a proton in a hydrogen atom is about 𝟐. 𝟐𝟕 𝒙 𝟏𝟎𝟑𝟗 times greater than the gravitational force between them.  The main force acting on the body is the gravitational force! Stability of the body against the gravitational force is maintained by the bone structure of the skeleton. Gravitational force W applies at the center of gravity (CG) of the body! CG depends on body mass distribution! To maintain stability, CG must be located between the feet. If feet are far apart forces in the horizontal direction Fx have to be considered. The main force acting on the body is the gravitational force! To maintain stability, the vector sum of all forces acting at CG must be zero. The influence of the gravitational force within the human body One of the main applications of gravitational force in a human body is visible in blood circulation. Role of valves in veins 1. Muscle contracts 2. Forces blood flow along the vessel 3. Valves keep the blood flowing towards the heart, against the gravitational force What happens when the valves do not work? What happens when the valves do not work? Blood flows in a reverse direction within the veins, along the direction of the gravitational force, called an incompetent vein. Role of gravitational force within the body ✓ Blood circulation ✓ Bone health ✓ Body weight What does gravity have to do with bone health? Imparts mechanical resistance to the body's activities. → Perceived by osteocytes and translated into cellular signals that regulate the balance between tissue formation (growth) and tissue resorption (breakdown), termed bone remodelling. What happens to our bones in space? Mass does not change on Earth vs. in space. Weight changes depending on the gravitational pull. Astronaut in the International Space Station (ISS) ❑ Downward gravitational pull of about 0.89 g, but the station itself is simultaneously accelerating downward at 0.89 g. Everyone and everything inside the station experiences the same gravity and acceleration → sum of the forces on the astronauts is close to zero. ❑ Microgravity – condition where people or objects appear to be weightless What happens to our bones in space? Calcium that is stored in the bones is broken down and released into the blood stream. Decreased bone density → higher concentration of calcium in blood. What happens to our bones in space? Serious problem on very long space journeys. Long-term bed rest is similar in that it removes much of the force of body weight from the bones which can lead to serious bone loss. Running in Space! (youtube.com) In space, the amount of weight that bones must support is reduced to almost zero. At the same time, many bones that aid in movement are no longer subjected to the same stresses that they are subjected to on Earth. Over time, calcium normally stored in the bones is broken down and released into the bloodstream. The high amount of calcium found in astronaut's blood during spaceflight (much higher than on Earth) reflects the decrease in bone density, or bone mass. Gravity and the human body - Jay Buckey (youtube.com) Question 1 The high amounts of calcium in the blood of an astronaut when he is in an orbiting satellite is a result of the: A. Specific diet B. Electric force C. Lack of gravitational pull D. Radioactivity in the orbiting satellite Question 2 Which is a correct statement about a force? A. Has direction only. B. Has direction and magnitude. C. Has magnitude only. D. Has neither magnitude nor direction. Question 3 Which of the following describes the result of the action of the gravitational force in the human body: A. Body weight. B. Formation of varicose veins in the legs. C. The a and b. D. None of the above. Question 4 If two forces of 20 N towards north and 12 N towards south are acting on an object, the resultant force will be: A. 32 N toward north B. 20 N towards north C. 32 N towards south D. 8 N towards north Question 5 State of equilibrium is when: A. there is no opposing force acting on the object B. there is no force acting on the object C. the object is moving in uniform acceleration D. the opposing forces acting on an object have equal action  Adding forces Force is a vector quantity If two or more forces are acting upon the body, they must be added as vectors. To practice: https://phet.colorado.edu/sims/html/forces-and-motion-basics/latest/forces-and-motion-basics_en.html Net force The net force is the vector sum of all the forces that act upon an object. That is to say, the net force is the sum of all the forces. The net force depends on the magnitudes and directions of the applied forces. Also known as resultant force. Net force Net force Forces are vectors (they have both magnitude Several different forces working at and direction) and so add as follows: In one dimension, note direction using a + or – once, all pulling or pushing with sign then add like scalar quantities (regular different strength, often in different numbers with no direction associated with them). directions. The effects of all these forces add The net force is the resultant of this vector addition: together or subtract from one another to produce an overall force Fnet = F = F1 + F2 + F3 +  (or perhaps no force at all). Resultant force: the sum of all the force vectors acting on the body. It is Bold letters represent vectors. The units of Force are Newtons, a single force which has the same or the abbreviation N, which effect as the combination of forces. Fnet = 2N represent the SI units: kg-m/s2 Example 1 Example 1 Example 2 Example 2 Equilibrium When you feel dizzy might someone tell you that you lost your equilibrium. Equilibrium: a state where an object remains at rest or continues to move with a constant velocity (i.e. it is not accelerated). When your body is in equilibrium, it is in a state where it is physically balanced. Equilibrium We also use the word equilibrium when talking about balance. ❑Only common way equilibrium comes up is when looking into the motion of an object. Different types of motion = different types of equilibrium. ✓Equilibrium means that the object remains at rest or continues to move forward with a constant velocity, i.e. it is not accelerated Common types of motion: Translational Rotational Translational motion Occurs when there is movement in a straight line. From one point to another point. Rotational motion Occurs when there is movement around an axis. An object revolves around an axis. Rotational + translational motion = rolling States of Equilibrium are associated with the types of motion. Translational equilibrium Vector sum of all the external forces acting on the body is zero. Object in translational equilibrium when experiencing zero overall acceleration → not moving or moving at a constant velocity. Translational = only changes of position are considered; changes of orientation of the object with respect to the axes are ignored. Both cars are in translational equilibrium. Example of translational equilibrium The earth pulls down with force W. The floor pushes up on the right foot with force N1 and on the left foot with force N2. Draw the free body diagram to determine what the condition for translational equilibrium tells us about the forces. The equilibrium condition gives: N1+N2-W = 0 or N1+N2 = W Total force on the floor pushing up on both = pull of the earth → translational equilibrium STATIC EQUILIBRIUM DYNAMIC EQUILIBRIUM Example 3 – for home The cast and the forearm together weigh 98.0 N. Assuming the upper arm exerts a horizontal force of 24.0 N to the right on the forearm, determine the force exerted by the sling on the neck. Force equilibrium problems like this can be analyzed by drawing a free-body diagram of the point of attachment which must be in equilibrium. Then you apply the force equilibrium condition. 24.0 N 98.0 N Example 4 Find the tensions required to support the mass. Play with this example at: http://hyperphysics.phy- astr.gsu.edu/hbase/fcab.html Example 4 Find the tensions required to support the mass. Conditions for equilibrium ✓ First condition ✓ Second condition The net external force on the Object must avoid accelerated system must be zero. rotation → maintain constant Expressed as an equation, this is angular velocity. simply A rotating body or system can be in equilibrium if its rate of net 𝐅=0 rotation is constant and remains unchanged by the forces acting on it. TRANSLATIONAL EQUILIBRIUM ROTATIONAL EQUILIBRIUM x  x PIVOT POINT  x PIVOT POINT  To rotate an object you need to apply torque. x PIVOT POINT Read more at: 9.2 The Second Condition for Equilibrium - College Physics 2e | OpenStax Rotational equilibrium The object does not rotate or continues to rotate at a constant rate (with a constant number of rotations per second). The condition for rotational equilibrium is that the sum of all torques is zero: Rigid rod free to rotate about a F3 pivot at point X: Forces F1 and F2 are applied to the rod at distances r1 and r2. The pivot exerts the force F3 on x the rod needed to maintain F1 F2 translational equilibrium. Translational equilibrium requires F1+ r1 r F2=F3 2 What is torque? https://demonstrations.wolfram.com/TorqueExertedOpeningADoor/ The turning or twisting effectiveness of a force. Has both magnitude and direction. Opening a door: Push on the side farthest from the hinges. Pushing on the side closest to the hinges requires more force. Although the work done is the same in both cases (the larger force would be applied over a smaller distance) people generally prefer to apply less force, hence the usual location of the door handle.  Same force is much more effective at rotating an object such as a nut or a door if our hand is not too close to the axis. That is why we have long- handed wrenches and why doorknobs are not next to hinges. Balanced torques A pair of torques can balance each other. Balance is achieved if the torque that tends to produce clockwise rotation by the boy equals the torque that tends to produce counterclockwise rotation by the girl. Torque Torque is a measure of the force that can cause an object to rotate about an axis. Torque is a vector quantity. The direction of the torque vector depends on the direction of the force on the axis. o a o Force vs Torque Forces describe changes in linear motion – which means changes in velocities. Torque describes how these same forces can change angular motion – which means changes in angular velocities. How is torque calculated? Torque is the cross product between a force and the distance of the force from a fulcrum (the central point about which the system turns). Torque - magnitude Figure 1 o a o Units: Nm [Newton meters] Torque increases as the force increases and as the distance increases. Torque - direction The direction of the torque vector is found by convention using the right hand grip rule. If a hand is curled around the axis of rotation with the fingers pointing in the direction of the force, then the torque vector points in the direction of the thumb. Interpretation of torque Only tangential component of force can cause torque. Why? Only tangential component of force can cause torque. Why? Radial component of force would produce translational movement → linear velocity. Torque requires angular velocity. Torque - direction Produces a counterclockwise angular acceleration = positive Produces a clockwise angular acceleration = negative Exerting lesser force for same effect. Torque - summary Question 6 Example 5 Calculate the force the biceps muscle must exert to hold the forearm and its load. 𝐹B – force of the biceps 𝐹E – force of the elbow joint 𝑤a – weight of the forearm 𝑤b – weight of the load 𝐹B and 𝐹E are unknown → cannot use the first condition of equilibrium. Use second condition and choose the pivot to be at the elbow → torque due to 𝐹E = 0. Example 5 The torques created by the weights are clockwise relative to the pivot, while the torque created by the biceps is counterclockwise; thus, the second condition for equilibrium (net 𝛕 = 0) becomes 𝑟2𝑤a+𝑟3𝑤b=𝑟1𝐹B Note that sin 𝜃 = 1 for all forces, since 𝜃 = 90º for all forces. Solving for 𝐹B Example 5 The force the biceps muscle must exert to hold the forearm and its load. Example 6 – for home The expression for the torque of the bicep muscle on the forearm is Schematic view of the muscle system used to bend the elbow. Biceps bend the elbow to lift, triceps straighten it. Example 7 – for home A 25 N force is applied to a bar that can pivot around its end as shown below The force is r = 0.75m away from the end and at an angle θ=60°. What is the torque on the bar? -16 N.m The torque is clockwise and therefore is negative. Example 8 – for home A uniform meterstick (1m stick) is balanced at its midpoint with several forces applied as shown below. If the stick is in equilibrium, the magnitude of the force X in newtons (N) is…... Applying rotational equilibrium the magnitude of the force X in newtons (N) is 50 Newton. Equilibrium in Medicine The equilibrium condition can be used to understand many problems in medicine (e.g. clinical orthopaedics) Example: Forces that cause the Achilles tendon to rupture. Example 9: Forces in the Achilles tendon Calculate the force exerted by this tendon on the calcaneus when a person is standing on the ball of one foot. FT= The force exerted by the tendon on the foot FB= The force of the leg bones (tibia and fibula) on the foot W= The force of the floor upward, which is equal to the weight of the body. Note: Measurements performed on several patients suggest that the angle the Achilles tendon makes with the vertical is about 7°.  155 Translational equilibrium requires that: FT cos(7°) + W – FB cosθ = 0 FT sin(7°) – FB sinθ = 0 7° Note: Measurements in a few people suggest that the angle the Achilles tendon makes with the vertical is about 7°.  156 Note: For rotational equilibrium we need to know Rotational equilibrium requires that: the torques. We assume that the torques are taken The torque equation is: about the point where FB is applied to the foot. 10W – 5.6 FT cos(7°) = 0 This equation can be solved for the tension in the tendon: FT = 10W / 5.6cos(7°) = 1.8W The tension in the Achilles tendon is nearly twice the person’s weight To find the: Fby=Fbcosθ From the previous slide we know: FT cos(7°) + W – FB cosθ = 0 & FT sin(7°) – FB sinθ = 0 7° (1.8)(W)(0.993) + W = FB cosθ 2.8 W = FB cosθ and FB = 2.8 W The force exerted on the leg (1.8)(W)(0.122) = FB sinθ by the talus is nearly three 0.22 W = FB sinθ times the body weight  157 FT = 1.8W The tension in the Achilles tendon is nearly twice the person’s weight, while the force exerted on the leg by FB = 2.8 W the talus is nearly three times the body weight. One can understand why the tendon might rupture. Question 1 a. Is it possible for an object to be in translational equilibrium (the first condition) but not in rotational equilibrium (the second condition)? Illustrate your answer with a simple example. b. Is it possible for an object to be in rotational equilibrium but not in translational equilibrium? Illustrate your answer with a simple example. Question 1 a. Is it possible for an object to be in translational equilibrium (the first condition) but not in rotational equilibrium (the second condition)? Illustrate your answer with a simple example. b. Is it possible for an object to be in rotational equilibrium but not in translational equilibrium? Illustrate your answer with a simple example. Question 1 – alternative example a. Is it possible for an object to be in translational equilibrium (the first condition) but not in rotational equilibrium (the second condition)? Illustrate your answer with a simple example. Yes. While starting to rotate, the ceiling fan rotates with positive angular acceleration to attain its maximum speed but it has zero linear acceleration. During this period, the fan is in translational equilibrium but not in rotational equilibrium  BE CAREFUL A body can be in translation equilibrium and not in rotation equilibrium and vice versa. Stability To maintain stability the sum of the forces acting on it in any direction and the sum of the torques about any axis must both equal zero. Levers in the Human Body The musculoskeletal system includes levers. Lever: a rigid rod, or arm, that turns about a pivot point, called the fulcrum. Force, or an effort, is applied to the lever arm to move a load, also called the resistance. Types of levers 1st class – EFL 2nd class – ELF 3rd class - FEL Levers increase mechanical advantage You can increase mechanical advantage by: ✓ Moving the fulcrum closer to the resistance and farther from effort force. Levers in the Human Body The human body is a complex machine that includes simple machines – LEVERS Many of the muscle and bone systems of the body act as levers (e.g. arms, legs work as levers to move and lift objects). In simple terms, a joint (where two or more bones join together) forms the axis (or fulcrum), and the muscles crossing the joint apply the force to move a weight or resistance. What type of levers do we have in the human body? Most human body levers are third class levers, while first-class levers are the least common. First class lever in the body I. The joint between the skull and the atlas vertebrae of the spine; the spine is the fulcrum across which muscles lift the head. II. The head atop the spinal cord, where the weight of the head is balanced by the downward effective force of the muscles. III. The triceps brachii pull on the ulna about the elbow pivot balanced by the forces on the forearm. With the upper arm down, the triceps brachii can balance an upward force pushing the hand up. First class lever Second class lever in the body I. The Achiles tendon, pushing of pulling across the heel or the foot. II. On the lower leg when someone is standing on his toes. Force is applied on the muscles by the weight of the body at the toes as an axis. III. Doing push ups using triceps. Second class lever Nutcracker Wheelbarrow Car door Third class lever in the body I. The elbow joint: when lifting a book, the elbow joint is the fulcrum across which the biceps muscle perform the work. II. Biceps curls: while lifting a dumbbell, the elbow joint acts as an axis with force applied on our hands by the weight we are lifting III. Raising the weight with the arm held straight Third class lever 1st class – the weight and muscle act on opposite sides of the fulcrum and are in the same direction 2nd class – the muscle and weight act on the same side of the fulcrum, and the weight is nearer to the fulcrum 3rd class – the muscle and weight on the same side of the fulcrum, but now the muscle is nearer to the fulcrum than the weight Levers in the human body Joints and levers in the human body || 3D Animation||Education Biology -YouTube Exercise 3 - for home Exercise 4 - for home Exercise 3 - for home SOLUTION Exercise 4 - for home SOLUTION Thank you! Waves and Resonance I Acoustic and Sound Waves Outline Types of waves Sound waves Perception of sound Frequency range Power and intensity Pitch Loudness vs Pitch Noise-induced hearing loss What is a wave? A WAVE is a vibration or disturbance in space. A MEDIUM is the substance that all SOUND WAVES travel through and need to have in order to move. Types of waves A wave is a form of energy transfer. MECHANICAL ELECTROMAGNETIC Needs a medium to propagate. Does not need a medium to propagate. i. Water ii. Sound i. X-rays ii. Radio waves iii. Light Direction of propagation Depending on the direciton of propagation, waves can further be categorized into: a. Transverse b. Longitudinal Direction of propagation TRANSVERSE WAVE The particles of the medium oscillate (vibrate) perpendicular to the motion of the wave. ❑E.g. water wave, electromagnetic waves travelling in a medium LONGITUDINAL WAVE The particles of the medium oscillate parallel to the motion of the wave. A longitudinal wave has two main sections: 1. Compression – an area of high molecular density and pressure 2. Rarefaction – an area of low molecular density and pressure  Particles of the medium oscillate parallel to the motion of the wave. COMPRESSION RAREFACTION Particles of the medium oscillate perpendicular to the motion of the wave. Each wave can be described by… ✓ The wavelength, 𝜆, is the distance between two successive maxima (“peaks”) or minima (“troughs”) in the wave. [m] ✓ The amplitude, 𝐴, is the maximal distance that a particle in the medium is displaced from its equilibrium position. [dB] ✓ The velocity, 𝑣⃗ , is the velocity with which the disturbance propagates through the medium. [m/s] ✓ The period, 𝑇, is the time it takes for two successive maxima (or minima) to pass through the same point in the medium. ✓ The frequency, 𝑓, is the inverse of the period (𝑓=1/𝑇). [Hz] Wave speed You can find the speed of a wave by multiplying the wave’s wavelength in meters by the frequency (cycles per second). Since a “cycle” is not a standard unit this gives you meters/second. Example 10 A harmonic wave is traveling along a rope. It is observed that the oscillator that generates the wave completes 40.0 vibrations in 30.0 s. Also, a given maximum travels 425 cm along a rope in 10.0 s. What is the wavelength? cycles 40 f = = = 1.33 Hz sec 30 x 4.25 v= = = 0.425 m/s t 10 vwave vwave = f →  = = 0.319 m f Sound waves Longitudinal mechanical waves that propagate through a medium. Sound is a sensation created in the human brain in response to pressure fluctuations in the air. As any object moves through the air, the air near the object is disturbed. The disturbances are transmitted through the air at the speed of sound. 1. Air pressure waves. 2. Tympanic membrane vibrates → transforms vibration into mechanical energy 3. Middle ear converts energy into hydraulic energy in the fluid of the inner ear. 4. Hydraulic energy stimulates the sensory cells of the inner ear, which send electrical impulses to the auditory nerve, brainstem, and cortex. Energy Conversion 1. Sound energy 2. Mechanical energy 3. Hydraulic energy 4. Chemical energy 5. Electrical energy Sound waves Sound is a longitudinal wave. Sound waves Sound is a longitudinal wave. ✓ Needs a medium to propagate. ✓ Particles move in a direction paralell to the direction of wave propagation. Sound waves Sound is a longitudinal wave. As the bell moves back and forth, the edge of the bell strikes particles in the air. 1. Bell moves forward → 2. Bell moves backward → particles driven forward particles driven backward i. Air particles bounce with i. Air particles bounce with Pressure variations greater velocity lower velocity transmitted through ii. Greater pressure ii. Lower pressure matter as sound waves. Sound waves Sound: mechanical disturbance generated by passage of energy through a medium. ✓ Source generates and propagates mechanical vibrations between the particles of the medium → sound wave Sound waves Imagine a material as an array of molecules linked by springs As an ultrasound pressure wave propagates through the medium, molecules in regions of high pressure will be pushed together (compression), whereas molecules in regions of low pressure will be pulled apart (rarefaction). As the sound waves propagate through a medium, molecules oscillate around equilibrium position. Propagation of sound waves Sound is characterized by the properties of sound waves (i.e. frequency, wavelength, speed, period, amplitude) Sound waves can propagate in solids, liquids and gases. Sound propagate as waves of alternating pressure, causing local regions of compression and rarefaction. The particles of the material transmitting this wave oscillate in the direction of propagation of the wave itself. Sound waves that are confined to the frequency range which can stimulate the human ear and brain, lead to the sensation of hearing. Sound vs. light SOUND LIGHT Mechanical wave Electromagnetic wave Longitudinal wave Transmit Transverse wave Amplitude tells you energy Amplitude tells you about about volume Do NOT intensity Frequency tells you transmit matter Frequency tells you about about pitch type of wave / color Speed in air 346 m/s Can reflect, Speed of light in air 3 x 108 Sound travels faster in diffract, interfere m/s and diffract most solids than it does Light slows down in solids in air Measured in Travels through vacuum The denser the medium, Herz (Hz) The denser the medium, the faster the wave the slower the wave Measured in decibels (dB) Perception of sound Sound is perceived through the sense of hearing. Hearing is one of the senses and refers to the ability to detect sound. Sound is detected by the ear and transduced into nerve impulses that are perceived by the brain. Frequency range of sound waves The human ear does not respond uniformly to sounds at all frequencies. Human can hear sounds with frequencies between 20Hz and 20kHz. Power and intensity of a sound wave Travelling sound waves transport energy from one point to another. A sound wave transports energy through a medium from a source. The energy is measured in Joules [J] Power (P) – rate at which the source produces energy. Measured in Watts [W], where 1 W = 1 J/s Intensity (I) – power per unit area. Measured in [W/m2 = dB] Power and intensity associated with a wave increase with pressure [p]. P∝p I∝p 2 Intensity is a measure of the amount of energy in sound waves. Intensity of a sound wave Pressures in two sound waves of different intensities. The more intense sound is produced by a source that has larger amplitude oscillations and has greater pressure maxima and minima. Higher pressure associated with more intense sounds → exerts larger forces on the objects it encounters. The loudness of a sound is determined by the intensity of the sound waves. Pitch of a sound wave The sensation of a frequency is commonly referred to as the pitch of a sound. A high pitch sound corresponds to a high frequency sound wave. A low pitch sound corresponds to a low frequency sound wave. Pitch of a sound wave Loudness vs. pitch Loudness vs. pitch Wavelengths of sound waves The shorter the wavelength, the higher the frequency, and the higher the pitch, of the sound. In other words, short waves sound high; long waves sound low. Noise-induced hearing loss Noise-induced hearing loss Noise-induced hearing loss (NIHL) occurs when structures in the inner ear become damaged due to loud noises. What part of the ear is damaged in noise-induced hearing loss? Loud noises primarily affect the cochlea, an organ within the inner ear. When you’re exposed to loud noises, cells and membranes in the cochlea can become damaged. Loud sound → stronger vibration → damage to cells & membranes in the Cochlea decibels [dB] Higher intensity = higher amplitude Thank you!