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Biomechanics > Definitions > Flashcards

Definitions Flashcards

1
Q

Kinetics

A

concerning the analysis of the forces acting on the body. (BASES)
“The study of the action of forces” Hall, 2012
“The branch of dynamics concerned with the forces that cause or tend to cause motion.” McGinnis, 2013

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2
Q

Kinematics:

A

concerning the analysis of the movements of the body. (BASES)
“The study of the description of motion including consideration of space and time.” (Hall, 2012)
“The branch of dynamics concerned with the description of motion.” (McGinnis, 2013)
A force is a push or a pull. A force accelerates or deforms (not in rigid-body mechanics) an object. Forces come in pairs: action and reaction. A force is something that can cause an object to accelerate (start, stop, speed up, slow down, or change direction). A force is known as a vector quantity (size and direction).
Characteristics: point of application, direction and its sense. (McGinnis, 2013)

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3
Q

Internal forces

A

forces that act within the object or system whose motion is being investigated. Internal forces are important if concerned with the nature and causes of injury, but they cannot produce any changes in the motion of the body’s centre of mass. Muscles can only produce internal forces, even though muscle forces can produce motion on the body’s limbs, but these motions will not change the motion of the body’s centre of mass unless external forces are acting on the system. (McGinnis, 2013)

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4
Q

External forces:

A

forces that act on an object as a result of its interaction with the environment surrounding it:
Non-contact forces (gravity).
Contact forces (air resistance, water resistance, ground…):
• Perpendicular component (normal reaction force): acting perpendicularly to the surface of contact
• Parallel component (friction): acting parallel to the surface of contact and opposes motion or sliding between the surfaces. (McGinnis, Chpt 1, 2013)

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5
Q

FRICTION

A

Friction arises when molecules of the surface are in contact and are interacting:

Friction force is proportional to the normal contact force and acts perpendicular to it e.g. pushing a book then adding another book on top. Adding weight (not mass!) would increase the normal contact force acting between the 2 surfaces but it would also increase the interactions of the molecules of the contacting surfaces, because they would be pushed together harder.
Friction is not affected by the size of the surface area e.g. if you stand the book on the table. The increase in the surface area increases the number of molecular interactions, but the decrease in pressure (force divided by area) decreases the magnitude of these interactions. Thus the net effect of increasing surface area is zero, and friction is unchanged.
The nature of the materials in contact affect the friction force between them e.g. placing a shoe compared to a book. The weight and mass of the objects are the same but the surface area changed. However that doesn’t affect the friction. So it is the difference in the type of material (soft and rough).
Static friction is greater than dynamic friction. It is harder to start something to get moving than to keep the object moving. (McGinnis, Chpt 1, 2013)

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6
Q

Colinear forces

A

are forces that have the same line of action. E.g. tug-of-war

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7
Q

Concurrent forces:

A

are forces that do not act along the same line but do act through the same point.

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8
Q

Static equilibrium

A

when an object is at rest and the forces are in equilibrium

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9
Q

A free-body diagram:

A

it is a mechanical representation and a useful tool for analyses. Only the object is drawn with all the external forces that act on it. (McGinnis, Chpt 1, 2013)

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10
Q

Compressive forces:

A

pushing forces act on the ends of an internal structure and the structure is under compression. (McGinnis, 2013)

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11
Q

Tensile forces:

A

pulling forces act on the ends of an internal structure and the structure is under tension (McGinnis, 2013)

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12
Q

Inertia:

A

the property of an object that resists changes in motion. Linear inertia is quantified as an object’s mass. Thus it is more difficult to speed up, slow down, or change the direction of a more massive object because it has more linear inertia.

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13
Q

Angular inertia

A

(rotary inertia): the property of an object that resists changes in its angular motion. It is more difficult to speed up, slow down, or change the direction of an object with more angular inertia (mass). Angular inertia is affected by mass and how the mass is distributed relative to the axis of rotation.

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14
Q

Angular momentum:

A

is the product of mass and velocity. Mathematically, angular momentum is a vector quantity, it has a size and direction

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15
Q

Scalar

A

A quantity that has only a magnitude

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16
Q

Speed

A

The rate of change of displacement with respect to time (vector quantity)

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17
Q

Velocity

A

The rate of change of distance with respect to time (scalar quantity)

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18
Q

vector

A

a quantity that has both direction and magnitude

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19
Q

acceleration

A

the rate of change of velocity with respect to time

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20
Q

displacement

A

change in position during a time interval (vector quantity)

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21
Q

Distance

A

length along a path an object has travelled (scalar quantity)

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22
Q

mass

A

the quantity of matter in an object

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23
Q

weight

A

the force that results from the action of a gravitational field on a mass

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24
Q

Force

A

A force is a push or a pull
A force accelerates an object.
Equation: F = m x a
Units: Newtons (N)
One Newton of force is defined as the force required to accelerate a 1 kg mass, 1 m/s2.
A force is a vector – it has a size (magnitude) and a direction.
Length of arrow indicates size.
Shaft/arrow indicates the direction and point of application.

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25
Q

Inertia

A

the property of an object to resist changes in its motion

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26
Q

Linear motion

A

movement along a straight or curved line where body parts move in the same distance and direction at the same time (a.k.a translation) e.g. skating

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27
Q

angular motion

A

motion around an imaginary axis with all body parts moving through the same angle at the same time (a.k.a rotation) e.g. gymnast swinging on bar

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28
Q

Angular velocity

A

the rate of change of angular displacement with respect to time

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29
Q

Curvilinear motion

A

the body moves along a curved path and still satisfies the condition of linear motion e.g. sky diving

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30
Q

General motion

A

very common in sport, usually rotation of some body parts resulting in translation of other body parts

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31
Q

Magnitude

A

The relative size of an object. The term for the size of a vector.

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32
Q

Stability

A

Resistance to both linear and angular acceleration to disruption of equilibrium.

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33
Q

Centre of Mass (CoM)

A

the point in a body or a system of bodies about which the weight is evenly distributed or balanced and through which the force of gravity acts.

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34
Q

Momentum (P)

A

The product of mass and velocity of an object.

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35
Q

Perspective error (2D Video Analysis)

A

The distance between the performer and the camera.
Errors:
If the object is behind the Plane of Motion (PoM) then the dimensions will be smaller.
If the object is in front of the PoM then the dimensions will be larger.
If the object is not parallel to the PoM then the angle and length of object will be wrong
To reduce error:
Increase the distance between the camera and the PoM.
Place the object parallel to the PoM.

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36
Q

Newton’s first law

A

the law of INERTIA: an object either remains at rest or continues to move at a constant velocity, unless acted upon by a net force

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37
Q

Newton’s second law

A

the law of ACCELERATION: the sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration a of the object: F = m x a

38
Q

Newton’s third law

A

the law of REACTION: When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.

39
Q

Running speed

A

step rate (Hz) x step length (m)

40
Q

Projectile

A

a projectile is an object that is subject to no external forces other than gravity.
If there is no air resistance, the projectile follows a parabolic path and the path is symmetrical by its APEX.

41
Q

Factors affecting long jump performance

A

Distance –> flight distance –> HEIGHT, SPEED and ANGLE of takeoff

42
Q

Resultant VELOCITY of a Projectile (i.e. hypotenuse in trigonometry)

A

Remember that RESULTANT means the sum of the vectors and that velocity is a vector. A projectile has a HORIZONTAL AND VERTICAL velocity. This means 2 VECTORS… so this can be calculated by using basic trigonometry: you can either use the Pythagorean theorem wich is a quicker and easier than using the SOHCAHTOA equation

43
Q

Take off ANGLE of a projectile

A

This is the ANGLE at which the Centre of Gravity (CG) is projected:
Using basic trigonometry, this can be calculated by using the equation: Arctan (vertical Take off velocity/Horizontal Take Off Velocity)

44
Q

What is the vertical acceleration of a projectile?

A

The vertical acceleration of a projectile is CONSTANT due to gravity (i.e. 9.8m/s2)

45
Q

What is the vertical velocity of a projectile?

A

The vertical velocity of a projectile is CONSTANTLY CHANGING during its flight. Indeed, velocity = displacement x time

46
Q

What is the horizontal acceleration of a projectile?

A

There is NO horizontal acceleration of a projectile during flight.

47
Q

What is the horizontal velocity of a projectile?

A

Air resistance can affect horizontal velocity. In most cases, the horizontal velocity of a projectile remains CONSTANT

48
Q

Vertical Motion is motion with constant……….., while horizontal motion is motion with constant………..

A

acceleration ; velocity

49
Q

Projectile motion occurs when objects are only under the influence of………. and……….

A

gravity ; air resistance

50
Q

The height of a projectile depends on……….

A

Initial Vertical Velocity

51
Q

The time of flight of a projectile depends on……….

A

Initial Vertical Velocity

52
Q

Horizontal motion of a projectile depends on……….

A

horizontal velocity and time of flight

53
Q

The Trajectory of a projectile is influenced by……..

A
  1. projectile speed
  2. Height of release (i.e. projectile height)
  3. projectile angle
54
Q

Apex

A

Point of Maximum Height of a projectile.

Vertical Velocity at Apex = 0

55
Q

SUMMARY of the Kinematics of Projectiles

Projectile motion

A

A projectile ignores air resistance, therefore only gravity affects it (i.e. vertical acceleration -9.81m/s2), the object follows a symmetrical (by its Apex) parabolic path. The projectile motion describes the path of the centre of mass (CoM) of the object.

  • Horizontal velocity = the same
  • Horizontal acceleration = 0
  • Vertical velocity before the Apex = positive and constantly changing
  • Vertical velocity after the Apex = negative and constantly changing
  • Vertical velocity at the Apex = 0

*Horizontal and vertical motion are independent of each other

56
Q

What does EAUM stand for?

In the three equations… what will always be the same?

A 
Equation of Uniformly Accelerated Motion
Only apply it to projectiles
In sport such as throwing events, jumping, gymnastics, etc...
In the Equations:
vertical acceleration (g) = -9.81 m/s2
horizontal acceleration = zero
Vertical acceleration = constantly changing
vertical velocity at the apex = 0
horizontal velocity remains constant
57
Q

Range (R) of a projectile = ………(2 ways)

A

R = horizontal velocity x time of flight
This is from EAUM 2nd equation:

displacement of body = initial velocity of body x time involved

or

R = initial velocity x cos Alpha (angle of projectile) x time of flight

58
Q

If an object takes off and lands from the same height and time of flight….. what will be the equation?

Remember that the projectile will be symmetrical by the apex so therefore Tup = Tdown

A

T = Tup + Tdown

Tup = V x sin Omega (angle of projection) / gravity

Tup = Tdown ==> that makes 2x

Therefore T = 2x (V x sin Omega / gravity)

59
Q

The effect of landing height from a projectile:

If the height of release is greater than the height of landing (h = +ve), the optimal angle is………..

If the height of release is lower than the height of landing (h = -ve), the optimal angle is……….

A

<45 degrees ; >45 degrees

60
Q

Static friction

definition

A

Also known as Surface or Contact friction:
When 2 surfaces are not moving relative to each other.
The force which opposes the onset of movement.

61
Q

Dynamic friction

definition

A

When dry friction acts between 2 surfaces that are moving relative to each other.

62
Q

Sliding friction

definition

A

The force which opposes the sliding of one body over another.

63
Q

Rolling friction

definition

A

The force which opposes the rolling of one body over another.

64
Q

laws of friction

A

Law 1: The force of friction is directly proportional to load (i.e. force perpendicular to the surface)

Law 2: The force of friction is independent of the apparent area of contact

65
Q

Mechanical work

A

The product of force and the amount of displacement along the line of action of that force.
There are two types of work: positive and negative work
Work = Force x Displacement
Units (N/m or Joules)

66
Q

Energy

A

Energy is the CAPACITY to do work.
There are two forms of mechanical energy:
1. Kinetic: energy due to MOTION.
2. Potential: energy due to POSITION or DEFORMATION. It has 2 forms:
a) Gravitational Potential Energy: Energy due to the object’s POSITION relative to earth
b) Strain Potential Energy: energy due to the DEFORMATION of an object.

67
Q

Kinetic energy

equation

A

Kinetic energy = 1/2 x Mass x Velocity²

68
Q

Gravitational Potential energy

equation

A

Gravitational Potential energy = Mass x Gravity x Height

Units: Joules or N/m

69
Q

Power

equation

A

Power = work / time
OR
(force x displacement) / time
Units: Watts

70
Q

Power

definition

A

The rate of doing work

71
Q

Torque

definition

A

Also known as Moment, is the rotational effect of an eccentric force

72
Q

Torque

equation

A

Force x Moment Arm (perpendicular distance)

Units: Nm

73
Q

Angular inertia

definition

A

Resistance to Angular Motion

74
Q

Angular Momentum

equation

A

H = I• Ѡ

75
Q

Mass is resistance to……….

A

linear acceleration

76
Q

Moment of inertia is resistance to……….

A

angular acceleration

77
Q

what are the 2 factors that affect moment of Inertia

A

mass

mass distribution around axis of rotation

78
Q

Moment of Inertia

equation

A

(single mass) I = mr²

(many masses) I = Σmr²

79
Q

Radius of Gyration

definition, practical example and symbol

A

Radius of Gyration (k): length from axis of rotation to a point where mass of the segment would be concentrated to produce an equivalent moment of inertia
Practical example: Sprinting – flexed knee redistributes mass in order to reduce distance of concentration of mass from axis of rotation which therefore reduces radius of gyration. Meaning the leg can be rotated forward faster and individual can run faster.

Spinning on chair – tuck in all body parts you will spin faster than if you are spread out. Due to smaller moment of inertia.

80
Q

Body segment

equation

A

I = mk²

81
Q

Angular momentum

symbol, equation and practical example

A

H = Moment of Inertia (I) x Angular Velocity (Ѡ)

Practical example: A diver performs a piked front somersault by transferring the angular momentum from the upper body to the lower body and vice-versa. Done by altering their body position which therefore alters their moment of inertia.

82
Q

First class lever definition

A

The applied force and the resistance force are on opposite sides of the fulcrum

83
Q

Second class lever definition

A

the resistance force is between the applied force and the fulcrum

84
Q

Third class lever definition + mechanical advantage + advantages + limitations

A 
the applied force is between the fulcrum and the resistance force
mechanical advantage <1
Advantage: maximise speed
distance lifted is larger
Limitations: Amount of weight lifted is
  limited
requires effort
  > resistance
85
Q

Wheel and Axle-like Arragement definition + examples in the human body

A

a wheel attached to an axle, both of which rotate about a common axis
Can either magnify force or increase the speed of motion – as for levers most maximise speed
E.g. Obliques or medial rotation at shoulder

86
Q

The kinetic Link Principle definition

A

Also known as the Summation of Speed. There is a sequence of acceleration and deceleration of links (segments) from proximal to distal, which results in a tremendous speed at the distal end.

87
Q

Pushlike patterns; describe when it would be used, its characteristics and the path it follows

A

Used when a large force must be applied
or when maximum accuracy of projection is required
Is characterised by the body parts moving the object forward from behind the object
Takes a rectilinear path, (more in a straight line)

88
Q

Define the Speed-Accuracy Trade Off + examples

A

In the performance of many skills, the outcome is determined by both speed and accuracy.
As the demands for accuracy increases, the speed of the movement decreases.
Examples: penalty kick in football, throwing a ball, long jump approach to take-off board

89
Q

what type of movement would be used in throwing to maximise velocity?

A

Throwlike movement

90
Q

what type of movement would be used in throwing to maximise accuracy

A

A pushlike motion

Biomechanics (1 decks)

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