Introduction to Biomechanics - Final Exam Notes PDF

Preview

Summary

Very thorough lecture notes - I received a high distinction in my final exam. ...

Description

BIOMECHANICS EXAM QUESTIONS 1) Define biomechanics The application of mechanical principles in the study of living things Preferred: The science concerned with internal and external forces and the effects these forces produce. 2) List 5 professional groups who benefit from a knowledge of biomechanics     

Physiotherapists for recovery, e.g. walking effectively Fitness instructors to maximise benefits, e.g. deadlif Podiatrists Sports physicians Coaches

3) Define and explain quantitative analysis Uses numbers to describe movement, e.g. height in high jump. Used by clinicians, coaches, teachers. 4) Define and explain qualitative Uses non-numerical description of quality, e.g. technique of a high jumper. Can be general or detailed for researchers and coaches. Important for both quantitative and qualitative to obtain the whole picture 5) Explain the difference between kinematics and kinetics using examples

 Kinematics is the description of motion or HOW it is occurring. Can look at spatial or temporal aspects. o How fast, what sequence of body segments, when action is performed  Kinetics is the study of the actions of forces or WHY it is occurring o Whether the amount of muscle force is optimal, momentum of body parts 6) List the SI units    

Length: Metre (m) Time: Second (s) Mass: Kilogram (kg) Temperature: Degrees Kelvin (K)

7) Define linear motion and provide two examples Motion in a straight or curved line Pure linear motion involves all parts moving the same distance, same direction, same time. May be:  Rectilinear – straight line  Curvilinear – curved line Examples include:  A skier in a static position down a hill is rectilinear  A skier goes over a jump and motion is curvilinear  A passenger sleeping in a plane at constant altitude is rectilinear  A passenger in a plane doing a backflip is curvilinear 8) How many types of linear motion are there Covered above 9) Define angular motion and provide two examples Body moves in a circular path around an axis of rotation so that all body parts move through the same angle, same direction, same time.

 A gymnast performing a full circle on the bar  A diver performs a somersault in mid air 10)Define general motion and provide two examples Combination of linear and angular motion  A Frisbee rotates and translates through the air  Walking  Throwing a ball consists of angular motion at the arm, linear motion of the released ball, and general motion of the body 11)What type is most common for human movement General 12)Describe the anatomical position Standing straight, arms by side, palms supinated/facing forward, feet slightly apart

13)Why is a standard anatomical position used in biomechanics Used as a reference point for defining movement terms. Allows standardised positioning and terminology so everyone can understand with others in the profession are talking about. 14)Name, define and provide a movement example of the three anatomical reference planes that divide body  Sagittal o Divides body into lef and right o Forward/backwards movement o Running or a forward roll  Frontal/coronal o Divides body into front and back o Side to side/lateral movement o Cartwheel or jumping jack  Transverse/horizontal o Divides body into top and bottom o Twisting motion o Ice skater spinning

 Note that these intersect at the centre of gravity 15)Name define and provide a movement example for the three anatomical axes that bisect the body  Mediolateral: Perpendicular to sagittal plane o Knee extension in kicking  Anteroposterior: Rotation in the frontal plane o Side bends  Longitudinal: Movement in transverse plane o Throwing a Frisbee 16)Mass is a measure of what? Quantity of matter in an object (kg) 17)Define inertia The tendency of an object to resist change in its motion. Directly proportional to mass. 18)Explain the difference between scalar and vector quantities and provide examples for each  Scalar: A quantity completely defined by its magnitude (size) o Mass, volume, time, speed, energy  Vector: A quantity defined by both magnitude and direction o Displacement, velocity, force, momentum, torque, weight 19)Why are arrows useful for vectors? Have both magnitude and direction. -

Head represents direction Length represents magnitude

20)When two or more vectors of the same quantity are added together what can be calculated? The resultant vector

21)Describe the process of adding vectors to find the resultant vector The tip to tail method 22)Is the order of adding vectors to find the resultant important? Nope 23)What is vector resolution Determining the perpendicular components of a vector quantity relative to a plane. Usually we break it down into horizontal and vertical. 24)Know Pythagoras’ theorem 25)Know trigonometry SOHCAHTOA 26)Motion that occurs in a straight line is called what Linear motion 27)Translational motion occurs when? Occurs in a straight line when all points on a body or an object move the same distance over the same time 28)Define linear distance provide symbols units and state scalar Distance (l) is the length between a start and finish point along a pathway.    

Measured length of the path followed A scalar quantity Symbol is l or d Units m

29)Linear displacement Displacement (d) is the straight line distance between the start and finish point with direction indicated  A vector quantity  Symbol d or s

 Units m (with direction) 30)Linear speed Speed (distance over time) is the rate at which a body moves from one location to another    

Distance (l) / time (t) A scalar quantity No recognised symbol m/s or ms-1

31)Linear velocity Velocity (v) is the rate at which a body moves from one location to another in a given direction    

Rate of change of displacement Displacement (d)/ time (t) A vector quantity m/s or ms-1 with direction

32)What quantity does the slop of a displacement-time graph provide? Velocity 33)The steeper the slope from a displacement-time graph would indicate what? Higher velocity

34)Explain the term ‘instantaneous velocity’ Velocity at a particular instance in time, e.g. javelin release velocity

35)Define linear acceleration, provide symbols, units and state vector Acceleration is the rate of change of velocity  Average acceleration = v2-v1/t2-t1  Change in velocity over change in time  A vector quantity

 Symbol (a)  m/s2 or ms-2 (with direction) 36)If the velocity of an object is changing quickly, then the acceleration of that object would be high, medium or low? High 37)The slope of which type of graph indicates acceleration? Velocity-time 38)When interpreting the direction of acceleration, explain how we differentiate between an object speeding up and slowing down Usually acceleration is +ve and deceleration is –ve Problems arrive when movement is in one direction and then the other, so we have to assign direction. In this case +ve value may not be acceleration, but is now the direction of travel. E.g. We say acceleration due to gravity is -9.81 m/s 2 39)What might an acceleration = 0 mean for a particular body? Travelling at a constant velocity

40)Any object thrown into the air is known as what? A projectile! 41)The flight pathway of a projected object is referred to as what? The trajectory 42)During human projectile motion, which body location is generally used for analysis The centre of gravity (COG) 43)In true projectile motion (objects in freefall), which two external forces act on the projectile? Gravity and air resistance

44)During projectile motion, which flight component does gravity affect?  Vertical component

 Gravity affects the height travelled.  Acceleration due to gravity = -9.81ms-2 45)During projectile motion, which flight component does air resistance affect?  Horizontal component  Air resistance affects distance travelled 46)When ignoring air resistance, what affect does the size, shape and mass of an object have on the acceleration of that object due to gravity? Acceleration due to gravity is independent of size, shape and mass.    

Vertical component of initial velocity determines the maximum height As a projectile gets higher the vertical velocity (Vv) decreases At max heart Vv = 0 As a projectile falls Vv is increasing in the negative direction

47)The flight path of a projectile that is not influenced by air resistance would follow a trajectory of which shape? Parabola – curved with an apex

48)A projectile at the apex of its flight is represented by a vertical velocity of? Vv = 0 49)For a projectile that is released from and lands at the same height (ignoring air resistance), the time taken for that projectile to reach the apex of its flight is equal to what percentage of the total flight time? 50% as the parabola is symmetrical when ignoring air resistance

50)List three release factors that affect the trajectory of a projectile  Projection angle – the angle at which a body is released with respect to the horizontal. Influences vertical, parabolic, and horizontal (half parabolic) trajectory.

 Projection speed – the magnitude of projection velocity. Influences the height and horizontal length of trajectory  Projection height – the difference between release height and landing height. Increases lead to more flight time and greater horizontal distance. 51)Define projection angle Done 52)In absence of air resistance, a projectile that is launched from a height of 2.5m with a projection angle of 0 degrees will produce a flight trajectory of which shape? Horizontal trajectory (a half parabola)

53)Define projection speed and state which components of a projectile’s trajectory that it can influence Done 54)What is meant by the relative height of release (height of projection) Done 55)What effect does increasing the height of projection have on a projectile Usually increases flight time and so increases horizontal distance 56)How can maximum range/distance be achieved in projectile motion We need to  Maximise speed of projection  Maximise release height without loss in release speed  Hit the optimal release angle for that release height 57)Describe how the optimum release angle for a projectile changes depending on whether the release height is greater, equal or less than the landing height Optimal release angle  When release height is 0 then optimal release angle is 45 degrees  As release height increases, optimal release angle decreases  As release height decreases, optimal release angle increases

E.g. a ball thrown up with a large horizontal angle will reach more height but less distance. E.g. in long jump 45 degrees would theoretically be optimum, but speed would suffer and this is more important. Elite angles = 18-27 degrees. E.g. in high jump the Fosbury flop is ideal at 40-48 degrees E.g. in shot put is ideal at 36-37 degrees

58)Under what conditions can the equations for uniformly accelerated motion be applied? Used when a body moves with constant acceleration. Solves problems where two quantities are known and we need a third. 59)Define and list several important features of Centre of Rotation  Needed to be identified so angles can be measured  Joint motion is ofen accompanied by displacement of one bone in respect to the other  Centre of rotation CHANGES  We look at the instant centre of rotation of joints (x-rays do this) 60)What is meant by the Instant Centre of a Joint The centre of rotation at a given joint angle or instant in time 61)What are the three conventional units used to measure angular motion Degrees, revolutions (rev) and radians (rad) 360 degrees = 2pi radians = 1 revolution 62)Which unit of angular motion is most appropriate for use in biomechanics? Radians which is dimensionless 63)Explain how to convert degrees to radians 1 radian = 57.3 degrees Therefore either divide (degrees to radians) or multiply (radians to degrees) by 57.3 64)Define relative angle  The angle at a joint formed between the longitudinal axes of adjacent body segments.

 No position in space, only the angle between two parts on the same side of the joint  Cosine rule for calculations 65)Full extension of a joint is considered to represent what angle? 0 degrees 66)Define absolute angle    

Angle between a body segment and a fixed reference line Usually just inclination from the horizontal or vertical Describes orientation in space because the reference line is spatial Use gradient formula for calculations from horizontal

67. List 4 tools that are commonly used for joint angle data collection in biomechanics.  Goniometer/protractor  Electrogoniometer which measures the electrical current changes caused by movement. Inexpensive but difficult when there is fat or muscle.  Motion analysis system. 2D and 3D video.  Accelerometers for dynamic use. Measures relative segment angles and accelerations. Expensive. 68. Explain the convention known as the Right Hand Rule and when it is applied. Fingers curl in the direction of rotation, the thumb points out to show the direction of the angular vector. 69. Define angular DISTANCE, provide its symbol/s, unit of measurement and state whether it is a scalar or vector quantity. Angular distance (ϕ:phi) is the sum of all angular changes that have occurred.  Scalar quantity  Measured in degrees

70. Define angular DISPLACEMENT, provide its symbol/s, unit of measurement and state whether it is a scalar or vector quantity. Angular displacement (θ:theta) is the smallest angle between initial and final positions of a rotating body.

 Vector quantity  Measured in degrees 71. Explain the convention used to define the direction of angular motion. Clockwise direction = negative Counter-clockwise direction = positive Consistent with the right hand rule 72. Define angular SPEED, provide its symbol/s, unit of measurement and state whether it is a scalar or vector quantity. Angular speed (σ:sigma) is the angular distance travelled per unit time.  It is scalar quantity  Measured in degrees/s or rads/s.  Angular speed can be found using the equation σ=ϕ/t o Angular speed = angular distance/time 73. Define angular VELOCITY, provide its symbol/s, unit of measurement and state whether it is a scalar or vector quantity. Angular velocity (ω:omega) is the rate of change of angular position.  It is a vector quantity  Measured in degrees  Angular velocity can be found using the equation ω = Δθ/Δt o Change in angle position/ change in time 74. Define angular ACCELERATION, provide its symbol/s, unit of measurement and state whether it is a scalar or vector quantity. Angular acceleration (α:alpha) is the rate of change of angular velocity with respect to time.  It is a vector quantity  Measured in degrees/s2 or rad/s2  Sign does NOT indicate direction of rotation o Apparently positive acceleration could mean decrease in velocity in a negative direction OR an increase in velocity in a positive direction. o So what the heck determines positive or negative? Acceleration/deceleration? But then isn’t a decreasing velocity always going to be deceleration so how could it be positive? 75. How can the linear distance of a point on a segment be calculated when that segment is undergoing rotation? Formula s = r θ

 S = linear distance  R = radius (distance between point and axis of rotation)  Θ = angular distance (ALWAYS IN RADIANS)

76. Define TANGENTIAL VELOCITY, provide its symbol/s, unit of measurement and state whether it is a scalar or vector quantity. The product of the point’s distance from the axis AND the angular velocity. VT = r ω ω = angular velocity (rad/s) VT = tangential velocity (m/s) r = radius of rotation (m

77. Explain how a hammer thrower could increase the tangential velocity of the hammer on release.  Increase the length of the chain – more radius of rotation  Increase spinning speed - more angular velocity 78. Define RADIAL ACCELERATION, provide its symbol/s, unit of measurement and state whether it is a scalar or vector quantity. Radial acceleration is the component of acceleration due to the rotation of a segment which represents the change in direction. It is given the symbol aR, and is a vector quantity. It can be found using the following equation Radial acceleration = (tangential velocity)¬2/radius length

79. Radial acceleration is also known as what and in which direction does it act? Radial acceleration is also known as centripetal acceleration and it is always directed to the centre of rotation 80. Define TANGENTIAL ACCELERATION, provide its symbol/s, unit of measurement and state whether it is a scalar or vector quantity. Rate of change of tangential velocity of a body following a curved path.  TA is measured in m/s2  A vector quantity  TA = TVf- TVi / t

81. Kinetics deals with which component of biomechanics? Addresses the causes of motion – WHY is that movement occurring? 82. Define FORCE, provide its symbol/s, unit of measurement and state whether it is a scalar or vector quantity. Force is any interaction (push or pull) between two objects causing acceleration.  Symbol is F  Measured in newtons (N)  Vector quantity 83. Objects move when acted upon by a force greater than……..? Their inertia. 84. Explain what is meant by the ‘Point of Application’ of a force and provide an example. The specific point where force is applied. For example in muscle contraction, force is applied at the centre of the muscle attachment to bone 85. Explain what is meant by the ‘Line of Application’ of a force. The straight line in the direction of acting force. Infinite length, and produces the same acceleration anywhere along the line.

86. Explain what is meant by the ‘Angle of Application’ of a force. The orientation of the line of application. Line of application relative to the segment it is applied to. Opposite to the joint angle ofen.

87. In relation to force systems, explain each of the following terms: Coplanar forces; Concurrent forces; Collinear forces; force Resolution. Forces are vectors with an angle of application and may have a number of forces acting on them. We can look at the different components (horizontal and vertical) or the net effect (resultant).  Coplanar forces are when multiple forces act in a single plane. Adding tip to tail gives the resultant  Concurrent forces act at a single point  Collinear forces act along a single line  Force resolution is breaking down the force into components with respect to coordinate system. Vertical and horizontal components found. 88. Newton’s 1st Law of Motion states that …... A body will remain in a state of rest or constant velocity unless acted upon by a net external force that changes the state of motion. 89. Newton’s 1st law of motion is also known as the law of what? Law of inertia. 90. Newton’s 2nd Law of Motion states that…… A net force applied to a body causes acceleration of that body of a magnitude:  Proportional to force  In the direction of the force  Inversely proportional to the body’s mass Remember F=ma 91. Newton’s 2nd law of motion is also known as the law of what? The law of accelaration

92. Newton’s 3rd Law of Motion states that …... For every action (force) there is an equal and opposite reaction 93. Newton’s 3rd law of motion is also known as the law of what? The law of reaction

94. When considering Newton’s Laws, explain why a person who applies a force to the ground in a vertical jump is projected upwards by the reaction force from the earth but the earth does not appear to experience movement as a result of the initial downward force from the person? According to Newton’s third law, the force exerted on the ground will be equal to the reaction force from the earth pushing back, projecting the person upwards. According to Newton’s second law, the acceleration is inversely proportional to the mass of the object. Since the earth has such a big mass it does not move. 95. Explain what is meant by ‘Non-Contact Force...