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Intro to Biomechanics > Week 2 - Linear Kinematics & Projectile Motion > Flashcards

Week 2 - Linear Kinematics & Projectile Motion Flashcards

1
Q

Define kinematics

A

the branch of dynamics concerned with the description of motion

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2
Q

Describe motion (2 points)

A
  • the action or process of a change in position
  • Two requirements for motion to occur: space to move in and time to move
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3
Q

State the forms of motion (6 points)

A
  1. Linear (translation)
    - Rectilinear - straight line
    - Curvilinear - curved pathway
  2. Angular (Rotation)
  3. General
    - Combination of 1 & 2
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4
Q

Describe Linear motion (10 points)

A
  • Also referred to as translation
  • All parts of a “body” move through the same distance, in the same direction, in the same time.
  • This can happen in two ways:
    • Rectilinear translation: all points of the body or object move in a straight line
    • Curvilinear translation: path followed by the points of an object move in a curved pathway
  • Examples:
    • figure skater gliding across ice in a static position
    • Sail boarder zipping across lake in a steady breeze
    • Skate boarder rolling along a section of concrete
    • Ski jumper
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5
Q

What are the steps to determine a linear motion? (8 points)

A
  1. Imagine two points on the object in question.
  2. Draw a straight line connecting the two points.
  3. Does the line:
    - Point the same direction
    - Stay the same length
  4. Do the lines:
    - Move in a parallel, straight lines? It’s rectilinear.
    - Move in parallel, non-straight lines? It’s curvilinear
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6
Q

Describe Angular Motion (5 main points, 20 points overall)

A
  • Also referred to as rotary motion or rotation
  • Many terms are used to refer to angular motion, such as:
    • Rotating
    • Spinning
    • Swinging
    • Circling
    • Turning
    • Rolling
    • Pirouetting
    • Summersaulting
    • Twisintg
  • All of these terms indicate that an athlete or object is turning through an angle or number of degrees
  • When all points of a body or object move in circles (or parts of circles) about the same fixed central line or axis.
  • Examples of movement which either include quarter turns (90 degrees), half turns (180 degrees), full turns (360 degrees) and/or revolutions (multiples of 360 degrees) :
    • Gymnastics
    • Skateboarding
    • Basketball
    • Diving
    • Figure Skating
    • Ballet
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7
Q

Describe general motion (7 points)

A
  • A combination of linear and angular motion.
  • Most movements in sport
  • Examples:
    • Running
    • Walking
    • Cycling
    • In these activities, the trunk of the body moves in a linear way, but this happens because there is angular motion occurring at the arms and legs
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8
Q

Define position

A

Mechanically, location in space

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9
Q

What descriptors can be used for movement? (3 points)

A
  • 1-Dimensional: a single number based on a fixed point of reference would be required to identify the position. For example, location of a sprinter from the start line
  • 2-Dimensional: two coordinates (y and x axes) are used to identify the position of an object. For example, the location of a soccer player on the field
  • 3-Dimensional: three coordinates or numbers (x, y and z axes) are needed to identify the position of an object: For example, the location of a squash ball during a match
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10
Q

What descriptors can be used for a change in position? (2 points)

A
  • Distance
  • Displacement
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11
Q

Describe displacement (6 points)

A
  • Shortest path between two points
  • “As the crow flies” termed used to describe displacement. For example: 200 m east as the crow flies
  • Vector quantity, meaning a quality defined by both magnitude (size) and direction
  • Straight line (as the crow flies) from the initial position to the final position
  • Metric unit = metre (m)
  • For example: 100 m East
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12
Q

Describe distance (3 points)

A
  • Total length of path between two points that is followed
  • Scalar, meaning a quality defined only by magnitude (size)
  • Metric unit = metre (m)
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13
Q

When is it appropriate to use distance vs displacement? (6 points)

A
  • Displacement magnitude and distance can be identical, however anytime the path of motion is not rectilinear the distance and displacement magnitude will differ.
  • For example, a run around a track could have a total distance of 4 m but if the start and finish location are the same, then the displacement is 0 m.
  • Distance: daily conversation.
  • Displacement: useful in mechanics
    • Short changes of position
    • How far and what direction
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14
Q

Describe speed (4 points)

A
  • Rate of motion (distance)
  • Scalar quantity
  • Defined as distance/time
  • Unit of measure is m/s
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15
Q

Describe velocity (5 points)

A
  • Rate of motion in a specific direction (displacement)
  • Vector quantity (magnitude and direction)
  • Can be positive or negative depending if direction of motion is positive/negative
  • Defined as displacement/time
  • Unit of measure is m/s
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16
Q

When is it appropriate to use speed vs velocity? (3 points)

A
  • If there is no change in direction or we are not concerned about direction speed & velocity are identical.
  • Average speed / velocity. E.g. over 100m sprint
  • Instantaneous speed / velocity: each moment in time, relative to the frequency with which data is recorded
17
Q

What is the equation of acceleration? (3 points)

A

Acceleration = Change in Velocity / Time
= final velocity - initial velocity / time

Unit of measurement = m/s2

18
Q

Define projectile

A

Anunsupportedbody or object that travels through air and once airborne the only forces acting on it are gravity and air

19
Q

What are the critical factors that affect projectile motion? (3 points)

A
  1. Angle of release
  2. Relative height of release
  3. Speed of release
19
Q

What are the factors that affect projectile trajectory? (3 points)

A
  1. Gravity
  2. Air resistance
  3. Initial conditions
20
Q

How does gravity influence projectile trajectory? (2 points)

A
  • Only affects vertical motion (Vv), horizontal velocity (Vh) remains unchanged
  • Flight path (TRAJECTORY) is a PARABOLA
21
Q

Define parabola

A

a plane curve which is mirror-symmetrical and is approximately U-shaped

22
Q

How does air resistance influence projectile trajectory? (3 points)

A
  • In most real-life situations, air resistance affects the horizontal component of projectile velocity.
  • An example: Ball thrown in an outdoor area will travel further if thrown with the tail wind rather than head wind
  • Because effects are variable, customary to disregard.
23
Q

How do the initial conditions influence projectile trajectory? (7 points)

A
  • Initial conditions that the projectile is release at will influence projectile motion. These include speed of release, relative height of release and angle of release
  • When analyzing projectiles, we can also consider factors such as
    • Time to max height
    • Maximum height
    • Vertical impact velocity
    • Flight time
    • Range
24
Q

What are the equations of projectile motion? (8 points)

A
  • v2= v1 + at
  • s = v1 t + ½ at2
  • v2 2 = v1 2 + 2as
  • v1 = initial velocity
  • v2 = final velocity
  • a = acceleration
  • s = displacement
  • t = time
25
Q

How is projectile motion used in sports? (4 points)

A
  • Maximising horizontal displacement is the objective of many sports, e.g. field throwing events
  • Maximising peak height for other sports, e.g. high jump, basketball jumpers
  • Some sports want long time in the air, e.g. gymnasts, lob in tennis
  • Some want minimum time in air, e.g. smash in volleyball, penalty kick in soccer
26
Q

Define range

A

Horizontal distance covered by a projectile

27
Q

What are the equation of range?

A

Range = Vh x Flight Time

28
Q

List the factors that influence projection range (6 points)

A
  1. Relative height of release
  2. Speed at release
  3. Angle at release
  • A change in any one of the three variables will affect the others and influence the range
  • When one factor is shifted closer to its theoretical optimum, another moves further away from its own optimum
  • In sporting events based on achieving maximum vertical or horizontal displacement of a projectile, the primary goal is to maximize the speed of projection
29
Q

Describe relative height of release (8 points)

A
  • Difference in the height from which the body is initial projected and the height at which it lands or stops.
  • If the projectile starts and finishes at the same height, then the relative height of release is 0. Example, in soccer the ball may be kicked of the ground and land back on the ground
  • If the object or body lands lower than than it is released, the relative height of release is positive. For example, javelin throwing or shot put
  • If the object or body lands higher than than it is released, the relative height of release is negative. For example, a football being kicked from the ground and landing in the hands of a player
  • Assuming same speed and angle of release, the projectile of the taller athlete will have more time in air. A taller athlete will throw further than a shorter athlete
  • Aim for positive height of release if attempting to maximize range, as produces longer flight time
  • Negative relative height of release decreases flight time & range, e.g. up hill shot in golf
  • As the height of the release increases the optimum angle decreases
30
Q

Describe projection speed at release (4 points)

A
  • The velocity of a projectile is split into two components: horizontal and vertical
  • When both vertical (Vv) and horizontal (Vh) velocity are equal, projection angle will be 45°
  • When Vv greater than Vh, projection angle will be greater 45° but no greater than 90°
  • When Vh greater than Vv, projection angle will be less than 45°
31
Q

Describe angle at release

A
  • Angle of release is determined by Vh and Vv and height of release
  • With a given velocity and height there is an optimum angle that results in the greatest range
  • Optimum angle: angle that results in the greatest range
  • If relative height of release is 0, optimum angle ALWAYS = 45°
  • If relative height of release is positive, optimum angle ALWAYS be less than 45°
  • If relative height of release is negative, optimum angle ALWAYS be greater than 45°

Intro to Biomechanics (6 decks)

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