Transcript Angular motion - Blyth-Exercise

Biomechanics
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“Nature and Nature’s laws lay hid in night. God said, ‘Let Newton be!’ and all
was light.”
- Alexander Pope, epitaph intended for Sir Isaac Newton
1
Intro to Biomechanics
1. What is biomechanics? What do biomechanists
study?
2. Explain the difference between quantitative and
qualitative analysis
3. Explain the difference between kinematics and
kinetics
4. List and briefly explain the 7 kinematic variables
5. Why is human motion so difficult to analyze?
6. Explain the three models used to analyze human
motion. Include a sport/activity example for each.
7. Briefly describe the three different types of motion
8. Define force, constant velocity, causes of linear
motion, causes of angular motion/moment of force
2
Biomechanics
• A science that examines the internal and
external forces acting on the human body
and the effects produced by these forces.
• What do biomechanists study?
– Skills: Why do some golfers slice,
hook, or hit a straight ball?
– Pain: How do orthotics relieve back
pain?
– Equipment: What are the fastest bike
tires?
– Safety: What is the best way to life a
heavy object?
3
Two Methods to Analyze Human Movement
Qualitatively
•Non-numeric descriptions
about movements
– Long, flexed, heavy,
poor, etc.
– How? Biomechanical
principles and
checklists
Quantitatively
• Numerical descriptions
• about movement
• Metres, mass, seconds,
Newtons, degrees, etc.
• How? Force plates, EMG
(electromyography), 3D
Imaging, etc.
4
Kinematics
Study of Motion
Kinetics Study of
Motion
• Focuses on the various FORCES
that cause a movement
 SPATIAL and TIMING
characteristics of motion
 Kinematic variables describe
linear and angular motion
 How long?
How far?
How fast?
How consistent?
Internal Forces:
 generated by muscles,
tendons, bones, etc.
 Cause body motion
External Forces:
 Forces acting on the body that
cause motion
 Force of gravity, friction, etc.
 Affects body motion
5
Kinematic Variables
• Time: temporal characteristics of a performance,
either of the total skill or its phases
• Displacement: length and direction of the path an
athlete takes from start to finish
• Angular Displacement: direction of, and smallest
angular change between, the rotating body’s initial
and final position
• Velocity: displacement per unit of time
• Angular Velocity: angular displacement per unit of
time
• Acceleration: rate of change of velocity
• Angular Acceleration: angular velocity per unit of
time
6
Biomechanical Models
of Human Motion
• Human movement is complex to analyze because:
– Forces being produced by the body
– Forces acting on the body
– Three dimensional nature of human movement
• The model used depends on:
– The question being asked
– The level of detail required
– The movement being analyzed
7
Biomechanical Models
of Human Motion
1. Particle Model:
 A simple dot representing the centre of mass
 Used when the human body or an object is airborne
 Eg: ball in flight, human diving or tumbling (projectile)
 Only forces are gravity and air resistance
 Limitations: Ignores the human form; easy to lose
track of the movement
8
2. Stick Figure Model
 2D body segments are represented by rigid bars
linked together by joints
 Used when the object is in contact with its
environment
 Used to represent the total body configuration for
gross motor skills that occur in 2 dimensions
 Eg: sprint starts, running, somersaults
 Limitations: cannot represent complex actions (grip
on ball, rotations)
9
3. Rigid Segment Model
 Body segments begin to represent true human form
(irregularly shaped 3D volume)
 Used for more sophisticated quantitative analyses
10
Particle Model
Stick Figure Model
Rigid Segment Model
Which biomechanical model of human movement would
you use to analyze...
Diver on a diving board
volleyball in the air
3d image of a wrestler
Tumbling gymnast
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Types of Motion
Linear motion
-
-
All body parts move in the same direction at the same
time
Translation: movement of the body as a unit without
individual segment parts of the body moving relative to
one another
Rectilinear motion: movement follows a straight line
Curvilinear motion: movement path is curved
Angular motion
-
When a body moves on a circular path and in the same
direction (aka rotation)
The body rotates around the axis of rotation
All joint motions are angular motions
General motion
-
A combination of linear and angular motion
Most athletics and everyday activities
12
Causes of motion
 The cause of motion of the human body is the
application of internal and external forces
 Force is a push or pull on a body; measured in Newtons (kg /m/s2)
 Constant Velocity occurs when an object is not accelerating
 Linear Motion is caused by forces which act through a body’s
centre of mass
 Angular motion is caused by forces that do not go through the
centre of mass
 A force causing angular motion is call a moment of force or
torque
13
Linear motion results when the forces
are applied through the centre of mass
Angular motion results when the forces
are applied away from the centre of mass
14
Forces
• Forces are represented by vectors
– Vectors have magnitude and direction
• Force of gravity (Fgrav) - equal to the weight of the object
• Applied force (Fapp) – force applied to the object
• Normal force (Fnorm) - the support force exerted upon an
object that is in contact with another stable object
• Friction force (Ffrict) - force exerted by a surface as an object
moves
across it
• Air resistance (Fair) – a frictional force that acts upon objects as
they travel through the air
Do You Know Your Forces?
1. An egg is free-falling
from a nest in a tree.
Neglect air resistance.
2. A sky diver is falling
from a plane to the
ground at constant
velocity. Consider air
resistance.
http://www.physicsclassroom.com/morehelp/recforce
/recforce.cfm
3. A book is at rest on a
table top.
4. A rightward force is
applied to a book in order to
move it across a desk with a
rightward acceleration.
Consider frictional
forces.
Analyzing Human Motion - Free Body
Diagrams
Free Body Diagrams: diagrams used to show the
relative magnitude and direction of all forces acting
upon an object in a given situation
17
Free Body Diagram Practice
• A lamp is at rest on a tabletop.
• An apple is free-falling from a tree. Neglect air resistance
• A flying squirrel is gliding (no wing flaps) from a tree to the ground at
constant velocity. Consider air resistance.
• A rightward force is applied to a box in order to move it across a desk with
a rightward acceleration. Consider frictional forces. Neglect air resistance.
• A force is applied to the right to drag a sled across loosely packed snow
with a rightward acceleration
• A car is coasting to the right and slowing down.
18
Levers
• Levers are a simple machine (anything
that can perform work). Work is the force
applied over a distance (W=Fd). Every
bone in our body acts as part of a lever
system to help us move.
• Class I-fulcrum (pivot point) is between the
force and the load. Both act in the same
direction. (teeter totter) in the body the
neck (flexion and extension) is this type. It
is weak.
Levers
• Class II-the load is between the fulcrum and the force and
they act is opposite directions (wheel-barrow). Very few in the
body, the ankle joint is one (ball of foot fulcrum, heel load
(down), muscle force (up). This type can move large amounts
of weight.
• Class III-the force is between the load and the fulcrum and
they act is opposite directions (shovel). there are many of
these in the body such as the biceps. The force (up) is
between the fulcrum (elbow) and the load (down) in your
hand. This type allows for great speed, but not maximal use of
the force.
• There are seven principles of biomechanical analysis.
• Jigsaw: each take two principles txt 231-234 and
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